Freshwater Fishes of Texas: A Field Guide

Key to the Families

Key to the Families This section is written in dichotomous format, which is a series of “yes” or “no” paired questions based on morphological characters that should identify each fish to only one family. The final step in the key leads you to the page where descriptions of species of that family begin. Morphological differences among families are relatively large and easy to recognize; thus the key can be used as quick reference to identify a fish, but it also highlights similarities and differences between the fish families. Unfamiliar terms encountered in the key may be found in the glossary. 1a. Jawless, mouth disc shaped; 7 pairs of external gill openings; paired fins absent; single nostril positioned medially . . . . . . . . . . . . . . . .Lampreys— Petromyzontidae (pp. 15–16) 1b. Mouth with jaws; paired fins present (pectoral or pelvic or both); 1 gill opening on each side of the head; 1 or 2 nostril openings on each side of the head . . . . . . . . . . . . . . . .2 2a. Body snakelike; lacks pelvic fins; dorsal, anal, and caudal fins joined . . . . . . . . . . . . . . . .American eel—Anguillidae (p. 25) 2b. Body more fishlike; caudal fin either heterocercal (backbone extending well into the upper lobe of caudal fin), abbreviated heterocercal (backbone only extending slightly into upper lobe of caudal fin, or homocercal (backbone does not extend into upper lobe of caudal fin and forms a hypural plate) . . . . . . . . . . . . . . . .3 3a. Caudal fin either heterocercal or abbreviated heterocercal. . . . . . . . . . . . . . 4 3b. Caudal fin homocercal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4a. Caudal fin heterocercal, body with bony scutes (plates)or appears scaleless. . 5 4b. Caudal fin abbreviated heterocercal; body covered with ganoid or cycloid scales . . . . . . . . . . . . . . . . 6  5a. Long, paddle-shaped snout; scaleless except for a few ganoid scales at the base of caudal fin . . . . . . . . . . . . . . . .Paddlefish—Polyodontidae (p. 18) 5b. Snout conical or shovel-shaped with four barbels on ventral surface; several rows of bony scutes (plates) along body . . . . . . . . . . . . . . . .Sturgeons— Acipenseridae (p. 17) 6a. Body covered with ganoid scales; snout formed into a beak; gular plate absent . . . . . . . . . . . . . . . .Gars—Lepisosteidae (pp. 19–22) 6b. Body covered with cycloid scales; snout not formed into a beak; gular plate present . . . . . . . . . . . . . . . .Bowfin—Amiidae (p. 23) 7a. One dorsal fin; pelvic fins without spines. . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 7b. One or two dorsal fins; pelvic fins with spines. . . . . . . . . . . . . . . . . . . . . . . .16 8a. Adipose fin present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8b. Adipose fin not present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 9a. Scales on body present; barbels on head absent. . . . . . . . . . . . . . . . . . . . . ..10 9b. Scales on body absent; barbels on head present; if barbels absent, body with bony plates . . . . . . . . . . . . . . . .11 10a. Fewer than 50 lateral line scales; incisor teeth present . . . . . . . . . . Tetras— Characidae (p. 92) 10b. More than 60 lateral line scales; incisor teeth absent . . . . . . . . . . . Trouts— Salmonidae (p. 106) 11a. Barbels absent, body covered with bony plates. . . . . . . . . . . . .Suckermouth catfishes—Loricariidae (p. 103) 11b. Scales absent; head with 4–8 barbels . . . . . . . . . . . . . . Bullhead catfishes— Ictaluridae (pp. 93–102) 12a. Head lacks scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 12b. Head partially scaled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 13a. Anal fin with 17 or more rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 13b. Anal fin with fewer than 13 rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 key to the families 10 14a. Belly with scales forming a sawlike keel . . . . . . . . . . . . . . . . . . . . . . Shads— Clupeidae (pp. 26–27) 14b. Belly without scales forming a sawlike keel . . . . . . . . . . . . . . . . . .Goldeye— Hiodontidae (p. 24) 15a. Inferior, fleshy mouth modified for sucking; more than 7 pharyngeal teeth in main row; usually 10 or more dorsal fin rays . . . . . . . . . . . . . . . . Suckers— Catostomidae (pp. 83–91) 15b. Mouth usually not fleshy or modified for sucking; fewer than 7 pharyngeal teeth in main row; usually 10 or fewer dorsal fin rays (excluding common carp and goldfish) . . . . . . . . . .Carps and minnows—Cyprinidae (pp. 28–82) 16a. Jaws duckbilled; caudal fin forked; lateral line present . . . . . . . Pickerels— Esocidae (pp. 104-105) 16b. Jaws not duckbilled; caudal fin rounded; lateral line absent. . . . . . . . . . .17 17a. Pelvic anal fins with 1–7 spines; 1–2 dorsal fins . . . . . . . . . . . . . . . . . . . . .20 17b. Caudal fin rounded; lateral line absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 18a. Mature males with rounded anal fin; males and females with third anal fin ray branched; no gonopodium present . . . . . . . . . . . . . . . .19 18b. Mature males with pointed anal fin forming a gonopodium; males and females with third anal fin ray unbranched. . . . . . . . . . . . . . . . .Livebearers— Poeciliidae (pp. 113-118) 19a. Body robust; teeth in single row are incisorlike and tricuspid (three points on a tooth) . . . . . . . . . . . . . . . .Pupfishes—Cyprinodontidae (pp. 127–29) 19b. Body elongate; conical (cone-shaped) pointed teeth in a single row or several rows . . . . . . . . . . . . . . . .Killifishes—Fundulidae (pp. 119–26) 20a. Anus anterior to pelvic fins (adults); more than 5 soft rays on each pelvic fin . . . . . . . . . . . . . . . .Pirate perch—Aphredoderidae (p. 107) 20b. Anus posterior to pelvic fins; 5...