Fishes of the Gulf of Mexico, Vol. 1

[ Natural History ]

Fishes of the Gulf of Mexico, Vol. 1

Myxiniformes to Gasterosteiformes

By John McEachran and Janice D. Fechhelm

This book is the first of two volumes that cover the entire fish fauna of the Gulf of Mexico.



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7 x 10 | 1120 pp. | 680 b&w illustrations, 257 line drawings, 1 maps

ISBN: 978-0-292-75206-1

The Gulf of Mexico is the ninth largest body of water in the world and contains over 15 percent of all known species of marine fishes. This diverse fish fauna has been the subject of many publications, but, until now, no work has ever surveyed all known species, including the deep sea fishes and those of the southern Gulf.

This book is the first of two volumes that will cover the entire fish fauna of the Gulf of Mexico. An introductory section that outlines the Gulf's geographical setting, geological origin, current patterns, tides, sediments, meteorology, ecology, and biological exploration is followed by a key for the forty-four orders of fishes known from the Gulf. Keys and descriptions are provided for families, which are arranged phylogenetically, and for the species, which are arranged alphabetically, described, and distinguished from similar species. All but a few species are illustrated.

Volume 2 is tentatively scheduled for publication in early 2006.

  • Acknowledgments
  • Introduction
    • Scope of the Book
    • Physical and Biological Description of the Gulf of Mexico
      • Overview
      • Geological History of the Gulf of Mexico
      • Currents and Tides in the Gulf of Mexico
      • Freshwater Input and Sediment Patterns
      • Meteorology
      • Biological Assemblages
    • History of Biological Exploration in the Gulf of Mexico
    • How to Identify Fishes
      • Names of Fishes
      • Structural Anatomy of Fishes
      • Measurements and Counts
    • Literature Cited
  • Fishes of the Gulf of Mexico
    • Key to the Orders of Fishes of the Gulf of Mexico
    • Myxiniformes
    • Petromyzontiformes
    • Chimaeriformes
    • Orectolobiformes
    • Lamniformes
    • Carcharhiniformes
    • Hexanchiformes
    • Squaliformes
    • Squatiniformes
    • Torpediniformes
    • Pristiformes
    • Rajiformes
    • Myliobatiformes
    • Acipenseriformes
    • Semionotiformes
    • Elopiformes
    • Albuliformes
    • Notacanthiformes
    • Anguilliformes
    • Clupeiformes
    • Siluriformes
    • Osmeriformes
    • Stomiiformes
    • Ateleopodiformes
    • Aulopiformes
    • Myctophiformes
    • Lampridiformes
    • Polymixiiformes
    • Ophidiiformes
    • Gadiformes
    • Batrachoidiformes
    • Lophiiformes
    • Mugiliformes
    • Atheriniformes
    • Cyprinodontiformes
    • Beloniformes
    • Stephanoberyciformes
    • Beryciformes
    • Zeiformes
    • Gasterosteiformes
  • Glossary
  • References
  • Index of Scientific Names

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Scope of the Book

This book is an attempt to provide a single reference to the identification and description of the fishes that occur in the Gulf of Mexico. Although much has been written on fishes of the Gulf of Mexico, the literature is scattered among a larger number of revisionary studies of higher taxa of fishes, many regional faunal studies of other areas, and countless short papers and notes in the primary literature. The proposed audience of the book is the scientists, students, and fishers with interests in the fishes of this region.

A key is provided for the 44 orders of fishes known to occur in the Gulf of Mexico. The orders and families are arranged phylogenetically, and keys are provided for all families within each order known to occur in the Gulf. Families within each order are described and distinguished from the other families of the order. Following the family accounts, keys are provided for all species within the family that are known from the Gulf. Each of these species is arranged alphabetically, described, and distinguished from the other species within the family, and most are illustrated. Information is provided on the distribution of the fishes, both within the Gulf and worldwide. Life history information is also provided for each species, but this information is greatly condensed because of the large number of species included. However, references are provided at the end of each species account for those interested in further information.

In some respects, the family accounts and especially the species accounts are redundant in that the same characters are covered for all families within an order and for all species within a family. Thus, as a result of our attempt to make the descriptions self-contained and as consistent as possible, portions of these descriptions may be very similar. Another approach would be to present a full description for the first family of each order and first species of each family within each order, and to simply discuss the distinctions of the remaining taxa of the order or family. This approach was judged to be too subjective, and it would make the descriptive material less available to the reader, who would have to turn to the account of the first family or species of the taxon to get a complete description of the family or species of interest. Alternatively, keys to and descriptions of the genera within each family could be provided. Many of the species descriptions would then occur once in the generic description. This approach would have shortened the book slightly by reducing the redundancy of the species descriptions. However, many of the genera that occur in the Gulf are widespread to worldwide, with numerous species outside the area covered by this book, and in many cases the morphological variation and total number of species within these genera are not well established. Thus descriptions of many of these genera would be vague or inaccurate. On the other hand, morphological variation within the families that occur in the Gulf is readily available (Nelson 1994). The value of the approach adapted for this book is that a reader can use the key to identify specimens at hand and then turn to the family or species account for a full description.

In keeping with the philosophy of making the descriptions as complete and as objective as possible, the family and species accounts are not comparative; that is, the taxon under discussion is not compared with related taxa. Such comparisons tend to be subjective and often are of little value in distinguishing between taxa.

The phylogenetic ranking and sequencing largely follow Nelson (1994), with several exceptions. Sphyrnidae are considered a family separate from Carcharhinidae despite the fact that carcharhinids are not monophyletic without inclusion of sphyrnids (Nelson 1994). The reason for maintaining this more traditional albeit nonmonophyletic classification is that the interrelationships within carcharhinids are poorly known and the sister group of the sphyrnids is not entirely clear. Squaliformes are classified into three families according to Compagno (1984), rather than into the four families recognized by Nelson, following the sequencing of Shirai (1992). Shirai divided Squalidae (sensu lato) into six families; however, some of these families are nearly as morphologically diverse as the entire order. Accepting Shirai's classification would cause problems in constructing keys and in defining the families, and his classification has not been rigorously tested. The electric rays (Narcinidae and Torpedinidae), the sawfishes (Pristidae), the guitarfishes and skates (Rhinobatidae and Rajidae), and the stingrays (Dasyatidae, Gymnuridae, Mobulidae, Myliobatidae, Rhinopteridae, and Urolophidae) are placed in separate orders rather than classified in the same order (Rajiformes) because they form natural groups (are monophyletic), and with the exception of the electric rays, they date back to the Jurassic or Cretaceous in the fossil record. These orders (Torpediniformes, Pristiformes, Rajiformes, and Myliobatiformes) are placed after the Hexanchiformes, Squaliformes, and Squatiniformes because the three orders of sharks plus the Pristiophoriformes and the four orders of rays are considered to constitute a monophyletic group (Shirai 1992). Halosauridae and Notacanthidae are placed in their own order (Notacanthiformes) rather than in the order Albuliformes with Albulidae. The two orders are thought to form a monophyletic group, but they are treated separately because of their distinctive body forms. Nelson follows Fink (1985) in lumping six of the families of Stomiiformes—Astronesthidae, Chauliodontidae, Idiacanthidae, Malacosteidae, Melanostomiidae, and Stomiidae—into a single family (Stomiidae). According to Fink, all six families constitute a monophyletic group, but some of the families, as traditionally recognized, are not monophyletic (do not share a common ancestor). To avoid further confusion by reallocating genera among the six families, Fink proposed lumping all of the genera within the six families into a single family (Stomiidae). The traditional view of the order is accepted herein because Fink's study has not been rigorously tested nor extensively used in the literature.

The information on the species composition of the Gulf of Mexico came from an extensive review of the literature and unpublished species lists, and from a survey of the natural history museums in the United States and Mexico. The following institutions all have extensive collections of fishes from the Gulf of Mexico: American Museum of Natural History (AMNH), New York, NY; Field Museum of Natural History (FMNH), Chicago, IL; Florida Museum of Natural History (FM), Gainesville, FL; Gulf Coast Research Laboratory (GCRL), Gulf Port, MS; Museum of Comparative Zoology (MCZ), Cambridge, MA; National Museum of Natural History (USNM), Washington, D.C.; Texas Cooperative Wildlife Collection (TCWC), College Station, TX; Tulane University Museum of Natural History (TU), New Orleans, LA; and Universidad Nacional Autónoma de México (UNAM), Mexico City. Considerable time was spent at these institutions developing lists of species previously unrecorded from the Gulf and using specimens to write descriptions and to prepare illustrations. When possible, illustrations were prepared partially or totally from museum specimens, but if specimens were unavailable or if available specimens were unrepresentative of the species, illustrations were adapted from those in the literature. In the latter case, when possible, the adapted illustrations were compared with museum specimens.

Because of the large number of species of fishes in the Gulf of Mexico, this book is divided into two volumes. This first volume treats the first 40 orders arranged in ascending phylogenetic sequence. The second volume, which will be published at a later date [late 2005 or early 2006 — UTP] ,will cover the remaining 4 orders.

Physical and Biological Description of the Gulf of Mexico


The Gulf of Mexico is a partially isolated body of water bordering the southeastern section of North America and straddling the Tropic of Cancer (Fig. A). With a surface area of 1,138,980 km2 and 4,000 km of coastline, it is the ninth largest body of water in the world. The maximum depth of the Gulf is 3,750 m in the Sigsbee Deep off Mexico. Its eastern border, and connection with the Atlantic Ocean and the Caribbean Sea, is a line from Key West to Cape Catoche. Thus its eastern border is west of both the Florida Keys and the coast of Cuba. The northern border of the Gulf of Mexico is formed by the shoreline of the U.S. states of Florida, Alabama, Mississippi, Louisiana, and Texas, and the southern border is formed by the shoreline of the Mexican states of Tamaulipas, Veracruz, Tabasco, Campeche, and Yucatán.

The Gulf of Mexico is both a warm temperate and a tropical body of water. The northern section, from Cape Romano, Florida, in the east to Cabo Rojo, Veracruz, in the west, is part of the Carolinian Warm Temperate Provence, and is separated from the remainder of the Carolinian Provence by the tropical, southern portion of the Florida peninsula (Briggs 1974). The southern section, south of the two capes, is tropical and contiguous with the tropical western Atlantic.

Low sandy banks or marshlands characterize the northern and southern shores of the Gulf, with extensive barrier beaches, dunes, salt marshes, and mangroves, depending on local conditions (Britton and Morton 1989). The coastline and continental shelves of the Gulf of Mexico are largely the result of three geological phenomena: alluvial deposits, biogenic limestone deposits, and orogenic volcanic deposits (Price 1954). Coasts and continental shelves of alluvial origin extend along the northern Gulf from Tamaulipas to the Florida Panhandle, and along the southern Gulf from Veracruz to western Campeche. Alluvial sediments have produced broad continental shelves (up to 210 km wide), with smooth shorelines of sandy beaches or barrier islands and rather smooth gradation of sediments, from sand inshore to mud, silt, or clay offshore. The coasts are often interrupted by river deltas, which are most extensive along the northern Gulf. Biogenic limestone, which formed in shallow marine areas during much of the life of the Gulf, dominates the coasts of Florida and Yucatán and has built continental shelves up to 160 km wide. In areas where land-derived sediments are scarce, the limestone platforms have become biogenic environments, supporting coral, mollusc, and other reef-building biota. Such communities thrive off the west coasts of Florida and Yucatán and on a variety of hard structures around the Gulf. Orogenic activity along the western Gulf of Mexico has resulted in a very narrow continental shelf, with the mountains' structural folds and faults paralleling the coastline.

The coastline is punctuated by a number of barrier islands and drowned river mouths that form estuaries. The barrier islands result from longshore transport of coastal sediments. When these islands form in front of river mouths, they give rise to primary bays with reduced exchange with the open Gulf through narrow tidal passes. Salinity of these bays is related to the magnitude of the freshwater source. Along the northern and southern coasts of the Gulf the salinities of the bays are brackish to hyposaline, while in the western Gulf, where river flow is minimal, the salinities are often hypersaline.

The sediments of the Gulf are a result of past geological events and present sediment patterns. The area east of DeSoto Canyon, southward along the Florida coast and along the west coast of Yucatán, is thickly covered with carbonate sediments, and the area west of this region is covered with thick terriginous sediments (Pequegnat et al. 1990). The northeastern Gulf is a carbonate bank that has been subsiding since the Cretaceous. The shelf off south Florida is a mosaic of soft sand and hard carbonate bottom covered with a thin veneer of sand (Antoine 1972). Rocky outcroppings are rare off south Florida except for the Florida Middle Grounds, which consist of steepprofile limestone escarpments and knolls rising 10 to 15 m above the sand and shell bottom. The Yucatán platform and Campeche Bank are very similar to the south Florida platform. In the northern Gulf, terriginous sediments increase westward of DeSoto Canyon. The shelf off the Florida Panhandle and Alabama is transitional, grading from sandy and shelly in the east to finer, terriginous sediments in the west. The northwestern Gulf is a geosyncline sinking under the weight of the terriginous sediments that have been deposited here over much of the life of the Gulf. The sediment pattern in this region has been altered by salt diapirism, or movement of salt upward through the overlying sediments. The salt was deposited early in the Gulf's history, when the Gulf was an evaporative basin, and prior to the tectonic forces that formed the deep-sea basin. The salt is rising through the sediments because it is less dense. The southern Gulf is similar to the northwestern Gulf in sediments and salt diapirism. Organic sediments, primarily from terrestrial sources, have also been trapped by the sediment load in the northern Gulf and have produced both petroleum and natural gas deposits. On the continental slope off Louisiana and east Texas there are over 40 locations of petroleum and natural gas seeps (Pequegnat et al. 1990). These areas possess rich, unique assemblages of invertebrate organisms. Chemoautotrophic bacteria are the primary producers of these communities (Childress et al. 1986).

Although terriginous sediments predominate in the northern Gulf, these sediments are punctuated by topographic features of diverse origins (Rezak et al. 1990). These features are present at various depths, but they serve as hard-bottom substrates for biota of the Gulf. The Flower Gardens Reef off Louisiana and east Texas is built on two salt-dome formations and is the most northern coral reef in the western Atlantic. Smaller reefs occur along the outer continental shelf off Alabama, and near shore off southern Texas, Tamaulipas, and Veracruz.

Geological History of the Gulf of Mexico

Recent plate tectonic studies suggest that the Gulf of Mexico has had a long and stable history. It formed as a result of the breakup of the supercontinent Pangaea that existed during much of the late Paleozoic and early Mesozoic eras, and in the subsequent breakup of Gondwanaland, the southern half of Pangaea, during the late Mesozoic and early Cenozoic (Pindell and Dewey 1982; Pindell 1985). In the Late Triassic (200 million years ago [Ma]), the Gulf region was occupied by continental blocks that were to become Yucatán, Florida, and the western Bahamas. About 165 Ma, northwestern Africa and South America began to separate from North America, and this rift resulted in sea-floor spreading north of the Blake Plateau and continental stretching in the area of the Blake Plateau and the Straits of Florida. These events caused the Yucatán block to separate from the area now occupied by Texas and Louisiana, and a chain of continental blocks, now comprising Mexico and northern Central America, to move southeastward into the area previously occupied by South America. The Mexican blocks previously abutted against the northwestern section of South America. As the Yucatán block moved away from Texas and Louisiana it rotated counterclockwise, and the area that it previously occupied became a marine basin, the Proto-Caribbean. The stretching of the continental crust in the Gulf region caused it to subside and dip below sea level. Subsequent breaching of the western land barrier led to the intrusion of sea water, and the Gulf region became a shallow evaporation basin forming the Louann-Campeche salt deposit. In the late Jurassic (150 Ma), sea-floor spreading began in the Gulf region, leading to a deep central basin and open circulation with the Proto-Atlantic Ocean between Florida and the Yucatán blocks. The open circulation and deepening brought an end to the salt deposition. During this period the blocks representing Mexico and northern Central America continued their southeastern rotation, and the Yucatán block continued to rotate counterclockwise until about 140 Ma, in the early Cretaceous, when the tip of the Mexican blocks and the Yucatán blocks became juxtaposed (joined). The uniting of the Mexican and the Yucatdn blocks brought to a close the horizontal plate motions associated with the opening of the Gulf of Mexico, and the Gulf of Mexico was formed.

Since its formation, the Gulf of Mexico has been rather tectonically stable. Its present physiography is largely due to marine carbonate deposition beginning in the Cretaceous, terriginous deposition in the west and central Gulf from the Late Cretaceous to the Eocene, severe sedimentary deposition and migration of salt upward along the northern and western Gulf that continues to the present time, and major changes in sea level that began in the Miocene.

One relatively recent tectonic event—closure of the trans-America sea passage at the end of the Miocene (5 Ma)—has had important effects on the Gulf of Mexico. Its closure forced the North Equatorial Current northward and thus formed or greatly strengthened the Gulf Stream. The latter swings into the Gulf of Mexico through the Yucatán Straits, between Cape Catoche, Yucatán, and Cuba, then moves westward to form the Loop Current that regularly penetrates to the mouth of the Mississippi River before turning eastward and exiting the Gulf through the Florida Straits. The Loop Current periodically gives off warm-core rings that spin off the Loop Current and move into the western Gulf. Both the Loop Current and the warm-core rings affect circulation and climate in the Gulf.

Currents and Tides in the Gulf of Mexico

The Gulf of Mexico is affected by three types of currents: currents related to the density of sea water, currents produced by the stress of winds, and tidal currents. In the eastern Gulf the pattern of sea-surface circulation is largely controlled by the influx of water from the tropical Caribbean Sea through the Yucatán Channel (176 km wide). Much of this water forms an S-shaped swirl that moves northwesterly, forming the Loop Current that flows southeasterly through the Straits of Florida (144 km wide) to form the Gulf Stream (Leipper 1954b, 1970). The northward and westward extensions of the Loop Current vary both seasonally and yearly but are known to intrude upon the continental shelf of the northern Gulf of Mexico to just east of the Mississippi River (Darnell and Defenbaugh 1990).

The western Gulf of Mexico is dominated by a cyclonic circulatory pattern in Campeche Bay, an anticyclonic pattern north of Campeche Bay, and a variable cyclonic pattern in the northwestern Gulf (Merrill and Morrison 1981). The southern cyclonic circulation is generated by wind stress. The anticyclonic circulation is fed by anticyclonic rings that are pinched off the Loop Current and migrate into the western Gulf (Elliot 1982; Kirwan et al. 1984), and by wind-generated currents (Sturges and Biaha 1976; Sturges 1993). The relative importance of the anticyclonic gyres and the curl of wind stress is a matter of debate (Sturges 1993). The cyclonic circulation in the northwestern Gulf is the result of a lowpressure trough formed when the Loop Current is fully extended into the eastern Gulf. When this occurs, a well-defined cyclonic coldwater gyre is formed from the trough, and it migrates westward to lie north of the anticyclonic gyre. The two-ring system causes eastward flow of surface water at about 24º30'N in the western Gulf. The northern cyclonic circulatory pattern is the most variable of the three systems in the western Gulf because a defined cyclonic gyre is only formed when the Loop Current is fully extended, and the Loop Current is not fully extended into the Gulf on a yearly basis (Merrill and Morrison 1981).

In winter the currents in the western Gulf are affected by northern winds, or "northers," that may cause fragmentation of westerly currents and reverse the direction of longshore drift of sediments.

The tides of the Gulf of Mexico are of rather low magnitude, ranging from 0.4 to 0.7 m in amplitude, and vary from diurnal (one high and one low tide per day) to mixed (varying between one high and one low per day to two lows and two highs per day) (Marmer 1954; Britton and Morton 1989). Despite the relatively small tidal amplitude, the extensive area of the continental shelves and the large number of shallow-water estuaries and lagoons can lead to significant tidal effects.

Freshwater Input and Sediment Patterns

The Gulf receives about 10.6 X 1011 m3 per year of freshwater, with about 85% of this coming from 44 major U.S. rivers. About 65% of the total is contributed by the Mississippi system alone (Darnell and Defenbaugh 1990). The Rio Grande has contributed little freshwater and sediments since the Miocene. The major Mexican freshwater sources—the Tonalá, Seco, Grijalva, Teapao, Usumacinta, San Pedro y San Pablo, and Palizada Rivers—enter the southern Gulf of Mexico.

These freshwater sources are also the major sources of terriginous sediments of the Gulf of Mexico, which dominate in the northern and southern Gulf. The Mississippi River is the dominant source of sediments, contributing about 4.1 X 1010 metric tons of sediment per year (Darnell and Defenbaugh 1990). Most of the sediment is deposited on the slope and the deep Gulf, but a significant amount is deposited on the shelves of Louisiana and east Texas (Darnell and Defenbaugh 1990).


The surface temperatures in the Gulf of Mexico during the summer are largely isothermal, about 29ºC, but surface temperatures increase from north to south in the Gulf during the winter months, averaging 18.3ºC in the north and 23.9ºC in the south (Leipper 1954a). The temperature gradient is greater in the east than in the west. The annual range of sea-surface temperature varies from about 5.6ºC to 8.3°C in the north and about 5.6ºC in the central and southern areas of the Gulf.

During the spring and summer the weather in the Gulf of Mexico is dominated by the Bermuda High. Air temperatures are high and uniform. Winds blow predominately from the southeast but are slightly more southerly in the northern Gulf and slightly more easterly in the southern Gulf. The higher water temperatures of the Gulf compared to those of the western Atlantic and eastern Pacific cause an increase in moisture content of the air over the Gulf and thus affect precipitation during the warmer months of the year. During the winter the winds blow more easterly, with occasional winds from the south and from the north. The southeasterly winds bring warm moist air from lower latitudes and transport it from the warmer waters of the southern Gulf to the colder waters of the northern Gulf. This circulation pattern leads to precipitation and fog in the northern Gulf.

During the winter the northern Gulf is subjected to 15 to 20 one- to three-day periods of north winds. These winds have speeds of about 20 knots and are capable of rapidly decreasing the land and inshore water temperatures along the northern coast, and the decrease often leads to spectacular fish kills.

The Gulf is subjected to hurricanes during the late summer and early fall, and about 80% of these form in the warm waters of the tropical Atlantic and enter the Gulf through the Straits of Yucatán. An average of nine hurricanes per year develop in the Atlantic, and many of these enter the Gulf. These storms are destructive to the biotas of the Gulf, especially to those living in bays and lagoons and over the shallow areas of the continental shelf, and to the humans living along the shoreline and coastal plain.

Biological Assemblages

Although soft sand to silty sediments are widespread, the habitats of the Gulf of Mexico are extremely diverse; in fact, the richness of habitats may rival those anywhere in North America (Britton and Morton 1989). The assemblages are demarcated by salinity, temperature, depth, and substratum.

The inshore waters vary from brackish to hypersaline, from warm temperate to tropical, and from silty mud to igneous rock or limestone reefs, and the biota vary with these habitat parameters. Estuaries are common habitats along the northern, eastern, and to a lesser extent, southern shores of the Gulf. They formed as a result of the drowning of river mouths after the last glacial period and by the formation of barrier islands. These habitats vary in salinity with the amount of freshwater flow and have soft, level floors of mud and silt. Estuaries are bordered by marsh grasses (Spartina species) in the northern Gulf and by mangroves in south Florida and in the southern Gulf. Despite high levels of sediment input, estuaries have stands of submergent vegetation such as Thalassia testudinum, Halodule wrigbtii, Ruppia maritima, and Syringodium filiforme, and oyster reefs, Crassostrea virginica. The grass beds and oyster reefs support distinct faunal assemblages, including a number of fish species. In general the fishes that inhabit estuaries are salt-tolerant (euryhaline) marine fishes. Euryhaline freshwater fishes have been less successful in occupying estuaries than their marine equivalents. Freshwater fishes occupy the more brackish areas in the estuaries and include sturgeons (Acipenseridae), gars (Lepisosteidae), killifishes (Cyprinodontidae), and livebearers (Poeciliidae). Estuaries serve as nursery grounds for a large number of marine fishes that live on the inner continental shelves, such as the anchovies (Engraulidae), herrings (Clupeidae), mojarras (Gerreidae), and drums (Sciaenidae). The fish faunal composition does not change with increase in salinity among estuaries except that species diversity declines with increase in salinity.

Mangrove habitats, which grow along tropical shorelines and estuaries protected from waves and high currents, provide a habitat for a variety of organisms. The dominant vegetation is the red mangrove Rhizophora mangle and the black mangrove Avicennia germinans that largely define the habitat of the coastline along southern Florida and much of Mexico. Fish fauna is similar to that found in the warm temperate estuaries of the northern Gulf except that diversity is higher because of the structured habitats provided by the mangrove roots. This substratum attracts gobies (Gobiidae), blennies (Blenniidae), and puffers (Tetraodontidae), in addition to sciaenids, grunts (Pomadasyidae), and gerreids. The mangrove habitats also serve as nursery grounds for a number of fishes that spend their adult life on coral reefs.

Along the seaside of barrier islands and coastlines devoid of estuaries, sandy beaches predominate. These habitats are rigorous environments for both animals and plants because of the surf and lack of cover. The fauna is dominated by burrowing bivalves and pelagic fauna. Fishes found along the sandy beaches include ladyfish (Elopidae), clupeids, engraulids, and juveniles of a variety of spiny-rayed fishes.

Natural rocky shorelines are uncommon in the Gulf, except for Veracruz, but artificial jetties and groins are now of common occurrence. These structures support fishes common on coral reefs that feed on attached algae and sessile invertebrates. Fishes frequenting this habitat include damselfishes (Pomacentridae), spadefishes (Ephippidae), wrasses (Labridae), puffers (Tetra odontidae), and filefishes and triggerfishes (Balistidae).

The continental shelf, a gently sloping plain extending to about 183 m in depth, extends outward from the shoreline. This habitat is rather extensive in the Gulf and supports several assemblages of fishes. From the shoreline to about 20 m the fish fauna is dominated by sea catfishes (Ariidae), lizardfishes (Synodontidae), and sciaenids. These fishes are heavily dependent on the estuaries as nursery grounds and are associated with the white shrimp Penaeus setiferus, and for that reason the assemblage is referred to as the white-shrimp assemblage (Chittenden and McEachran 1976). Seaward of the white-shrimp community to a depth of about 40 to 50 m, on muddy bottoms, the fish fauna is dominated by pogies (Sparidae), batfishes (Ogcocephalidae), searobins (Triglidae), sea basses (Serranidae), and left-eyed flounders (Bothidae). These fishes are largely independent of the estuaries as nursery grounds and are associated with the brown shrimp Penaeus aztecus. Thus this assemblage is referred to as the brown-shrimp assemblage (Chittenden and McEachran 1976). At the same depth, but on shelly or hard bottoms, is a slightly different assemblage dominated by snappers (Lutjamdae) and other spiny-rayed fishes with a preference for hard substrata.

The outer continental shelf is less affected by seasonal temperature cycles and has a soft mud to silty bottom. Fishes dominating this habitat include hake (Phycidae), scorpionfishes (Scorpaenidae), and ogcocephalids.

The Gulf also has extensive areas of hard substrata that support coral-reef assemblages. The west coasts of Florida and Yucatán possess the majority of these habitats, but a large-scale reef complex also occurs off western Louisiana and eastern Texas, the East and West Flower Gardens Reefs (Bright and Cashman 1974), and in several areas off the east coast of Mexico. These habitats support diverse fish assemblages dominated by morays (Muraenidae), serranids, butterflyfishes (Chaetodontidae), angelfishes (Pomacanthidae), wrasses (Labridae), and gobies (Gobiidae).

The continental slope extends from the edge of the shelf to about 2,000 m. This region has little sunlight; cold temperatures (4ºC to 12ºC); and soft, silty bottoms. Cutthroat eels (Syriaphobranchidae), macrourids (Macrouridae), and cusk-eels (Ophidiidae) dominate this habitat. The continental rise extends from the slope to the bottom of the Gulf. Eels of various families as well as synaphobranchids, macrourids, viviparous brotulas (Bythitidae), and ophidiids are the abundant fishes in this habitat.

The pelagic waters are traditionally divided into three subdivisions: the epipelagic realm, from the surface to 200 m; the mesopelagic realm, from 200 to 1,000 m; and the bathypelagic realm, below 1,000 m. The epipelagic zone is subdivided into the area that overlies the continental shelf (neritic zone) and that seaward of the continental shelf (oceanic zone). The neritic zone has two main assemblages, one associated with flotsam and Sargassum weed and one associated with the open water. The former includes fishes generally associated with the bottom over the continental shelf, such as the Sargassum fish (Antennariidae), Sargassum pipefish and dwarf seahorse (Syngnathidae), and many postlarvae and juveniles of species of spiny-rayed fishes. The open-water assemblage is dominated by requiem sharks (Carcharhinidae), clupeids, engraulids, flying fishes (Exocoetidae), mullets (Mugilidae), jacks (Carangidae), and some mackerels (Scombridae). The oceanic zone has mako sharks (Lamnidae), manta rays (Mobulidae), tunas (Scombridae), billfishes (Xiphiidae and Istiophoridae), and ocean sunfishes (Molidae). The lower section of the epipelagic zone in many respects has a distinct fauna, consisting of the poorly known oarfishes and relatives (Lampridiformes), in addition to fishes with great depth ranges (Lamnidae, Scombridae, and Xiphiidae). The mesopelagic realm is below the photic zone and in the permanent thermocline. The bristlemouths (Gonostomatidae) and lanternfishes (Myctophidae) dominate this realm, and many of these undergo daily vertical migration into the epipelagic zone. The bathypelagic zone receives very little to no sunlight, and temperatures range from 4ºC to 10ºC. Deep-sea anglerfishes (Ceratioidei) dominate this realm in most seas, but they are poorly known from the Gulf of Mexico. Numerous species of gonostcmatids and scaleless black dragonfishes (Melanostomiidae) are found in the bathypelagic zone in the Gulf.

History of Biological Exploration in the Gulf of Mexico

Compared with the fish assemblages of the eastern and western coasts of North America, the fish assemblages of the Gulf of Mexico are poorly known. The reason for this is a combination of the relatively recent development of major fishery industries and the lack of longestablished oceanographic and marine biology institutions and laboratories in the Gulf of Mexico.

The earliest surveys were land based and relied on seining and hook-and-line fishing or on obtaining samples from commercial fishermen with access to small fishing vessels. Spencer F. Baird and Charles Girard (1854) and Girard (1858, 1859) reported on fishes from Brazos Santiago, mouth of the Rio Grande; Saint Joseph's Island; Indianola and Galveston, Texas, collected on the United States-Mexican Boundary Survey. G. Brown Goode and T. H. Bean (1878, 1879, 1880, 1882a,b), and later David S. Jordan and Charles H. Gilbert (1882, 1884, 1885), published on the fishes from the Florida Gulf coast provided for them in part by Mr. Silas Stearns. Mr. Stearns worked for the Pensacola Ice Company and later for Warren and Company, wholesale fish dealers. Both companies dealt with the red snapper fishermen that worked the "snapper banks" between Pensacola and Tampa Bay. Stearns obtained rare and unusual fishes caught on the bank and also fishes disgorged by the red snappers that were the mainstay of the fishery. For over a decade Mr. Stearns collected specimens of these fishes and shipped them on ice or in spirits to Goode and Bean at the U.S. National Museum in Washington, D.C., or to Jordan and Gilbert at Indiana University in Bloomington, Indiana. Jordan and his students also traveled to Pensacola to assist Mr. Stearns with the collections and to collect fishes along the shoreline with seines.

Goode and Bean (1882a) published a list of nearly 300 species of fishes representing 80 families reported from the Gulf of Mexico, and Barton W. Evermann and William C. Kendall (1900) wrote a checklist of the fishes of Florida, including about 300 marine species from the Gulf coast of Florida. They also included an annotated bibliography of previous studies on Florida fishes.

During the 1880s Jordan and associates also collected fishes at Key West and Cedar Key, Florida; New Orleans, Louisiana; and Galveston, Texas, for the U.S. National Museum. He and Gilbert also made a large collection of fishes from Veracruz and Tampico, Mexico, from fish markets in Mexico City and from seining along the coasts. These fishes were reported on by Jordan and Dickerson (1908). Barton W. Evermann and William C. Kendall (1894) made extensive inshore fish surveys at Galveston and Corpus Christi. The early records of fishes of the Gulf were summarized in "Fishes of North and Middle America" (Jordan and Evermann, 1896-1900).

The first surveys aboard research vessels were conducted by United States Coast Survey steamer Blake in 1872 and between 1877 and 1880 (Galtsoff 1954). The expeditions, especially those from 1877 and 1880, obtained a wealth of benthic, mostly invertebrate specimens. The 1,000-ton U.S. Fish Commission steamer Albatross first visited the Gulf of Mexico in 1884 and explored the waters around the west coast of Cuba. The following year the ship returned to make more detailed explorations around Cozumel Island on the eastern edge of Campeche Bank, the red snapper banks of Cape San Blas in the northeastern Gulf, and the west coast of Florida to Key West (Collins 1887). Fishes collected during these surveys were described by Goode and Bean (1896).

From 1895 to 1913 the U.S. Commission of Fish and Fisheries steamer Fish Hawk explored the oyster and sponge grounds and made hydrographic observations along the northern Gulf of Mexico from the west coast of Florida to Matagorda Bay, Texas. Some of the fishes collected during these surveys were reported on by Evermann and Kendall (1898). In 1917 the U.S. Bureau of Fisheries research ship Grampus studied shrimp and fishery grounds from Key West, Florida, to Aransas Pass, Texas, and many of these species were reported on by John T. Nichols and Charles M. Breder (1922, 1924).

Extensive biological surveys, however, did not begin until 1950 when the Fish and Wildlife Service initiated a comprehensive research program in oceanography and fisheries resources of the Gulf of Mexico. The surveys were conducted aboard the USS Alaska and USS Oregon, with the Oregon mainly responsible for exploration of fishing grounds. Fish specimens resulting from these surveys were deposited at the National Museum of Natural History, the Museum of Comparative Zoology at Harvard University, and the Field Museum of Natural History in Chicago, and served as the material for numerous species descriptions. The stations occupied and fishes collected between 1950 and 1955 are listed in Springer and Bullis (1956). Later surveys between 1956 and 1960, by the succeeding vessels Oregon II and Silver Bay, were reported by Bullis and Thompson (1965).

The Gulf Biologic Station was one of the first marine biological stations in the Gulf. Located at Calcaseau Pass in Cameron, Louisiana, it was mainly concerned with oyster and other bivalve research and was operational from 1902 to 1910. Weymouth (1911) described a collection of fishes made by a Mr. Milo Spaulding of the Biologic Laboratory. The Carnegie Institution of Washington, D.C., established a marine laboratory at Loggerhead Key, Dry Tortugas, in 1904. Over his 25-year tenure at the lab, William H. Longley gathered data on the local fishes. His notes and manuscripts were published after his death by Samuel F. Hildebrand (Longley and Hildebrand 1940, 1941). These works are still important references on the fishes of the Florida Keys and the eastern Gulf of Mexico.

Louisiana State University maintained a small laboratory on Grande Isle from the late 1920s to the early 1950s that was mainly concerned with teaching. The Marine Laboratory of the University of Miami (now the Rosenstiel School of Marine and Atmospheric Science) was opened in 1942 in Coral Gables, Florida, for research and the teaching of oceanography and marine biology. Although the lab is located outside the Gulf of Mexico, it has greatly contributed to our knowledge of fishes of the Gulf. Students trained at the lab have made significant contributions to ichthyology, both of the Gulf and elsewhere. The state of Mississippi opened its Gulf Coast Research Laboratory at Ocean Springs, Mississippi, in 1947. Researchers at this lab have made major contributions to our knowledge of fishes of the northern Gulf of Mexico and have built a fine collection of fishes from the Gulf of Mexico and the Caribbean Sea. The Institute of Marine Science of the University of Texas in Port Aransas, Texas, was established in 1948 and has contributed to our knowledge of fishes of the northwestern Gulf of Mexico. Texas A & M University established the Department of Oceanography in 1949, and later acquired a marine lab and maintained a series of oceanographic vessels in Galveston. The vessel Alaminos of the University, under the direction of Willis Pequegnat, made large and important collections of slope and abyssal fishes of the Gulf of Mexico and the Caribbean Sea in the 1960s and early 1970s. Researchers in the Oceanography Department at Texas A & M University were the first to thoroughly investigate the fauna of the Flower Gardens Reefs (Bright and Cashman 1974; Bright et al. 1974). The Texas Game, Fish and Oyster Commission opened a marine laboratory in 1949 at Rockport, Texas, that contributed papers on fishes of Texas in the 1950s and 1960s. The Oceanographic Institute of Florida State University established a laboratory at Alligator Harbor in 1949, primarily for teaching, and has produced a large number of ichthyologists concerned with the Gulf of Mexico. The Fish and Wildlife Service opened a laboratory in Sarasota, Florida, and a laboratory in Galveston in 1950 for oceanographic and biological studies of the Gulf. The Alabama Marine Resources Laboratory established a laboratory on Dauphin Island in the 1960s, and this lab has trained a number of ichthyologists that published on the fishes of the northeastern Gulf of Mexico.

From the 1930s to the present our knowledge of the fishes of the Gulf and the number of investigators of this fauna have greatly increased. Some of the more significant, but by no means all, of these contributors are briefly mentioned below. Gordon Gunter was employed by the Institute of Marine Science of the University of Texas and later by the Gulf Coast Research Laboratory, and he published on fishes of the northern Gulf coast from the 1930s to the 1950s. J. L. Baughman worked at the Texas Game, Fish and Oyster Commission at Rockport and published a number of studies on the fishes of the Texas coast. Stewart Springer published extensively on the sharks of the Gulf and the Caribbean Sea while employed with the Fish and Wildlife Service from the late 1940s to the 1960s. Henry B. Bigelow and William C. Schroeder described many species of sharks and rays from the Gulf of Mexico and the Caribbean Sea, largely based on specimens caught by the USS Oregon, RV Oregon II, and RV Silver Bay. Isaac Ginsburg of the U.S. National Museum published a number of papers on fishes of the Gulf of Mexico and was one of the first to report on the subtle differences between fishes from the northern Gulf of Mexico and the southeastern coast of the United States. In the 1950s Henry Hildebrand (1954, 1955) contributed two seminal papers on fishes associated with the shrimp grounds of the Gulf of Mexico. G. K. Reid (1954) described the ecology of fishes in the northeastern Gulf of Mexico. Marion Grey, an ichthyologist at the Field Museum, wrote extensively on the deep-sea fishes of the Gulf of Mexico, mainly based on specimens captured by the Oregon. Giles W. Mead published several papers on Gulf of Mexico fishes and prepared an unpublished annotated list of fishes from the Gulf of Mexico while employed with the Fish and Wildlife Service. He listed over 800 species of bony fishes from the Gulf. Ralph W. Yerger contributed to our knowledge of the fishes of the Gulf of Mexico through his teaching and research during his tenure at Florida State University. Chuck E. Dawson wrote extensively on the systematics of fishes of the Gulf of Mexico and the Caribbean Sea during his tenure at the Gulf Coast Research Laboratory. John C. Briggs (1958) compiled a list of Florida fishes and discussed the biogeography of fishes in the Gulf of Mexico, in addition to writing a number of papers on fishes of the Gulf and the Caribbean Sea. G. B. Smith, H. M. Austin, S. A. Bortone, R. W. Hastings, and L. H. Ogren (1975) and G. B. Smith (1976) described the distribution and ecology of reef fishes in the eastern Gulf of Mexico. J. G. Walls (1975) published a book entitled Fishes of the Northern Gulf of Mexico. F. Sonnier, H. D. Hoese, and J. Teerling (1976) published observations on fishes associated with offshore reefs and platforms off Louisiana. H. Dickson Hoese (1958) prepared a checklist of marine fishes of Texas, and in collaboration with Richard H. Moore (1977), prepared a book on the marine fishes of Texas, Louisiana, and adjacent waters that dealt with 497 species. E. O. Murdy (1983) wrote Saltwater Fishes of Texas and recorded 540 species of fishes on the continental shelf of Texas. Victor Springer published a number of manuscripts on sharks, blennies, and gobies, and a classical study on the fishes of Tampa Bay, with K. D. Woodburn (1960), while employed with the Fish and Wildlife Service. Royal Suttkus, a professor at Tulane University from the 1950s through the 1980s, published a number of papers on fishes but is best known as a collector. During his tenure at Tulane he singlehandedly built one of the largest collections of fishes in the world. C. Richard Robins of the Rosenstiel School of Marine and Atmospheric Science published extensively on the fishes of the Gulf of Mexico and the Caribbean Sea, built a large collection of fishes, partially from the Gulf, and trained a large number of ichthyologists who in turn have contributed to our knowledge of fishes of the Gulf of Mexico. He and G. Carleton Ray wrote, and John Douglass and Rudolf Freund illustrated A Field Guide to Atlantic Coast Fishes of North America (1986), which includes shore and continental fishes from the northern one-half of the Gulf of Mexico. José Luis Castro-Aguirre (1978) published a systematic list of the marine fishes of the east and west coasts of Mexico and with Alba Márquez-Espinoza (1981) published an annotated list of the fishes of the Isla de Lobos and adjacent areas of Veracruz. Robert L. Shipp, a professor at the University of Alabama, published on the fish fauna of the northeastern Gulf of Mexico, including an identification guide (1988). R. M. Darnell et al. (1983) and Darnell and Kleypas (1987) published distributional atlases of the more common shorefishes and penaeid shrimps of the northwestern and northeastern Gulf of Mexico. Edward Houde, while at the Rosenstiel School of Marine and Atmospheric Science, conducted extensive studies of fish larvae distribution in the northeastern Gulf of Mexico.

These scientists and many others have set the stage for a comprehensive survey of the fishes of the Gulf of Mexico. Although additional species may be discovered and additional records may be recorded, the Gulf of Mexico has been thoroughly surveyed for fishes, and most of this information is available, although scattered, in the literature. It is hoped that organizing and consolidating this information will stimulate more comprehensive studies of fishes and other marine biota of the Gulf and contiguous areas.

How to Identify Fishes

Names of Fishes

Fishes and other organisms are classified into inclusive hierarchical systems that, as close as possible, reflect their evolutionary or genealogical relationships. Species are grouped into a genus with other species that are thought to share a common ancestral species. Genera are grouped into a family with other genera, families are grouped into an order, and orders are grouped into a class using the same criteria. The studies of the diversity and the evolutionary relationships of organisms are called systematics and phylogenetics, respectively, and one of the goals of these disciplines is to classify organisms into natural (monophyletic) groups (higher taxa). We can never be sure that our classifications totally reflect evolution because evolution is ancient history and humans were not around to directly observe it.

The basis of the study of organismic evolution is the species, which is defined as "groups of interbreeding natural populations that are reproductively isolated from other such groups" (Mayr 1969) or, alternatively, as "a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate" (Wiley 1978). Obviously neither of these definitions is easy to use because it is difficult, if not impossible, to determine whether or not two or more groups of organisms are reproductively isolated or form a single lineage. It can only be inferred that two or more populations will or will not interbreed if they are geographically isolated from each other. Also, populations that are geographically separated at the present time may not be isolated in the future, thus it can only be inferred that they either will or will not maintain their identity if their ranges should overlap at some time in the future. It is also becoming apparent that distinct species do interbreed occasionally. In most cases the decision to consider a population a distinct species, rather than a population of a more inclusive species, is arrived at by indirect means. The distinctions are usually based on differences in morphology, counts of repetitive characters (e.g., fin rays, gill rakers, vertebrae, etc.), coloration, or behavior between or among populations. More recently scientists have been relying on electrophoretic studies of proteins, chromosome numbers and shapes, and base sequences of mitochondrial or nuclear DNA. Populations that exhibit no overlap in any of these characteristics are usually considered distinct species, based on the assumption that the differences are the result of genetic differences either between or among the populations. However, not even the DNA data can provide, in all cases, a definitive answer to the species question. Thus the status of some species, even well-studied species, is controversial.

The formal or scientific name of a fish (a species) is binomial, consisting of a generic and a species name (epithet), followed by the describer and the date of the description. When the author's name is in parentheses, the generic name has been changed since description of the species. The generic name begins with a capital letter and the species name with a lowercase letter. Both names are based on Latin, as a result of its use by early scientists as the language of science, and are italicized to designate their formal status. A genus name can be used only once in zoology, and a species name can be used only once per genus, thus the species binomial is a unique combination accepted by scientists regardless of their native (vernacular) language. In zoology this binomial system dates back to the tenth edition of Carl Linnaeus's Systema Naturae, January 1, 1758. Linnaeus's system ended much confusion in biology by establishing a stable nomenclature. Today we recognize rules regarding the priority and codes for naming species and higher taxa.

Despite this system of nomenclature that has served the zoological community for nearly two and one-half centuries, there are moves afoot to establish formal vernacular names to be used in parallel with the scientific names. Obviously, separate vernacular names will be needed for each language, and scientists and interested lay people speaking different languages will have trouble with the vernacular names even if these names are well stabilized. One might ask why ichthyologists (those who study fishes) are spending time and energy to complicate a system that has worked for so long.

In addition to the potential confusion of the vernacular usage, there are other reasons for suppressing the use of common names, including loss of information, improper grammatical construction, the nonsensical nature of some of the proposed names, and disregard for the describer's intentions. A binomial name offers considerable information regarding the species. The generic name is applied to species that putatively share a common origin, and thus the generic name furnishes information regarding the species. Species that are included in the same genus, in most cases, will share a number of attributes related to appearance, habitat preferences, and other niche parameters. Common names generally offer no such information. Species in the same genus often have common names that do not reflect their affinities. For instance, according to the Common and Scientific Names of Fishes from the United States and Canada, 5th edition (Robins et al. 1991), the common name of Haemulon album is the margate, H. aurolineatum is the tomtate, and H. carbonarium is the caesar grunt. The vernacular names offer no information as to the genus of these three congeners, and it is debatable whether they will be any easier to remember than the scientific names. Occasionally the common names join together several nouns as adjectives, and these often include the names of other animals! For instance, the ophichthid eel Myrichthys maculosus is the tiger snake eel. The nettastomid eel Facciolella gilberti is the dogface witch-eel. The stomiid Stomias boa is the boa dragonfish. The scorpaenid fish Scorpaena bergi is the goosehead scorpionfish. At face value these names may be regarded as nonsensical. In some cases, common names may not be nonsensical but anthropomorphic, as in the common name of the ophichthid eel Lethogaleos andersoni, which is the forgetful snake eel, and the name of the balistid Aluterus heudeloti, which is the dotterel filefish. Finally, authors carefully choose names for new taxa, and these names often provide information regarding the appearance, life history, or locality of the taxon. Or an author may name the taxon for the collector or for a person that has made important scientific contributions. Often the common name selected by committee does not honor the author's original intent. For many of these species for which common names have been provided, only scientists will encounter them, because it is doubtful that many will enter the aquarium trade or will find their way into fish markets. Scientists supposedly rely on the scientific names of fishes, so why has the scientific committee spent the energy proposing common names?

In this book, the accepted common name of the species will be given if available, but no common names will be proposed for those species that currently lack them. The above discussion is presented as a plea to avoid another "Tower of Babble," or an unavoidable reduction of the informational content in the science of ichthyology.

Structural Anatomy of Fishes

Most fishes are bilaterally symmetrical, with the head flowing smoothly into the trunk, and the body bearing three or four vertical fins and two sets of paired fins (Fig. B). One or two dorsal fins occur along the midline of the back, usually behind the head. The caudal fin is located at the posterior end, and an anal fin occurs on the midventral surface between the origin of the caudal fin and the vent or cloaca. The paired pectoral fins are located behind the head, and the paired pelvic fins are variously located near the ventral midline from under the head to just anterior to the vent or cloaca, and occasionally on the midflank. One or more of these fins may be lacking in certain fish taxa. In fact none of these fins are universally present in fishes. The fins consist of fin rays and membranes uniting the fin rays, and the structure of both varies among phylogenetic assemblages of fishes.

The head of fishes varies in shape and relative size, but it bears most of the sense organs in all fishes. The mouth varies in position, from on top of the head (superior), to in front of the head (terminal), to under the head (inferior), and is variously endowed with lips, barbels, cirri, or fimbriae. The nasal openings (nares) are usually paired and located on the sides or on top of the head anterior to the eyes. Small pits or canals occur in various patterns on the head and these serve as openings for the lateral line system. This sensory system is concerned with the perception of the displacement of water (near field sound) in the vicinity of the fish. The eyes vary in size and orientation but are usually located on the upper sides of the head. Eyes may be reduced or totally absent in fishes that live in the deep sea or other lightless environments. The gills are usually located behind the cranium but are considered part of the head. They open separately to the outside in most jawless fishes and elasmobranchs but are covered with a bony plate (opercular bones) in bony fishes. The body and, in some cases, parts of the head are covered with scales, and the structure, shape, and distribution of scales vary among the various assemblages of fishes. Chondrichthyans have placoid scales that have the same structure as teeth. The primitive bony fishes are covered with bony scutes or ganoid scales. The remainder of the bony fishes have thin cycloid or ctenoid scales. However, some bony fishes lack a scaly covering, while others are covered with a bony armor.

Teeth of fishes vary in shape, structure, and location. In the chondrichthyans the teeth are restricted to the jaws, are imbedded in the gums, and are continuously replaced. In bony fishes teeth are associated with a number of bones and are usually embedded in the bone, and replacement is less regular than in the cartilaginous fishes. Teeth occur along the margins of the mouth, which include the premaxilla and maxilla in the upper jaw and dentary bone in the lower jaw in primitive bony fishes but only the premaxilla and dentary in derived bony fishes. Teeth can also occur in the roof of the mouth in the medial vomer and parasphenoid, in the lateral palatine and pterygoid bones, and in the floor of the mouth in the tongue (basihyal bone). Additional teeth can occur in the branchial bones that support the gills, especially on the pharyngobranchs and the basibranchs. The branchial bones also bear one or two series of gill rakers on the anterior aspects of the epibranch and the ceratobranch that aid in straining food items from the water that passes over the gills.

Variations in these basic structures will be presented in the family descriptions that follow.

Measurements and Counts

The methods of making the measurements utilized in the species descriptions are illustrated in Figure B. All measurements are made from point to point by means of dial calipers or dividers. Care must be taken when using nonrigid devices such as tape measures because these can overestimate linear distances. Length of fishes is expressed in terms of total length (TL), which is the distance from the tip of the snout to the distal extension of the caudal fin, or in terms of standard length (SL), which is the distance from the tip of the snout to the base of the caudal fin, at the end of the bony plate (hypural plate) supporting the fin rays. Standard length is the preferred length in systematics because it limits the variation caused by wear and damage to the caudal fin. Head length is measured from the tip of the snout to the distal margin of the operculum, and body depth is measured as the maximum depth of the specimen. The other measurements specific to particular fish taxa are described at appropriate sections of the text.

A number of counts are important in the description and identification of fishes. The fin ray counts follow those recommended by Hubbs and Lagler (1958). Fin spines are unpaired and unsegmented, and fin rays are segmented, bilaterally paired, and often branched. In many of the bony fishes, the last ray of the dorsal fin and the anal fin is separated to the base; in these cases the split ray is counted as one. Transverse scale row numbers and lateral line scale numbers are often included in descriptions. The former count includes all of the scale rows between the opercular flap and the base of the caudal fin. The latter count includes the number of pored scales between the opercular flap and the base of the caudal fin. Other counts, specific to particular taxa, are introduced at the appropriate sections of the text. Gill rakers are usually counted on the first arch only. These are reported as the total number on the epibranch and ceratobranch or separately for the epibranch and the ceratobranch. One or two gill rakers occasionally occur in the corner between the ceratobranch and epibranch, and these may be included in the total count or listed separately. In some taxa, gill rakers occur on the hypobranch, and if so, they are listed.

[Literature citation section omitted from this excerpt. —UTP]

By John McEachran and Janice D. Fechhelm

The authors are members of the Department of Wildlife and Fisheries Sciences at Texas A&M University, where John D. McEachran is Professor and Janice D. Fechhelm is Research Assistant and Scientific Illustrator.

"This work is unique and especially important because it brings together, for the first time, information on the entire fish fauna of the Gulf of Mexico. Other volumes cover only subsets of Gulf fishes....This represents the most complete survey of the ichthyofauna of the Gulf of Mexico ever compiled."

—Philip A. Hastings, Research Scientist and Curator of Fishes and Invertebrates, University of Arizona

Also by Author

Fishes of the Gulf of Mexico, Vol. 2 MORE +