This key is designed to assist the angler in identifying any fish found in Yosemite waters. It is a key of alternate characters, e.g., if the character opposite 1a is not typical of the specimen, you then proceed to 1b. For example: to identify the brown trout it would be necessary to use the following characters: 1a, 2a, 3b and 6a. Where practicable, the most usable single recognition character is in bold face type. The page on which you may find a description of that fish is indicated after each name.

1a. Ventral fins abdominal (attached considerably behind the pectoral fins).

2a. Adipose fin present.
3a. No red or brown spots present. Black spots on a background of lighter color.
4a. Body profusely covered with black spots. Sides not golden.
5a. Red stripe on sides of body. No red dash of color below lower jaw on each side.
RAINBOW TROUT, Salmo gairdnerii irideus p. 6
5b. No red stripe on sides. Body usually covered with black spots. Red dash of color in cleft under each side of lower jaw in adults.
CUTTHROAT TROUT, Salmo clarldi. p. 7.
4b. Black spots relatively few and mainly above midline. A yellowish-orange band on sides grading into golden-yellow farther down and finally orange on the abdomen. Body of stream fish with distinct bars or parr marks throughout life. Ventral and anal fins tipped with white.
—GOLDEN TROUT, Salmo aqua-bonito. p. 8
3b. Red or brown spots present. Background either brownish-yellow or strongly mottled with olive and black.
6a. General color brownish-yellow. A few red or brown spots present on sides. Back covered with brown spots. Lower fins and abdomen yellow to white.
—BROWN TROUT, Salmo trutta fario. p. 9
6b. Red spots on a background of darker color. Back unspotted but mottled with olive and black wavy lines. Lower fins edged with white stripe; bright red or orange behind this.
—EASTERN BROOK TROUT, Salvelinus fontinalis. p. 10

2b. Adipose fin absent.
7a. Mouth directed downward, excessively protractile with sucker-like lips.
—SACRAMENTO SUCKER, Catostomus occidentalis. p. 12
7b. Mouth not especially directed downward. Lips not enlarged and sucker-like.
8a. Upper lip with frenum (a small piece of flesh binding the upper lip to the edge of the jaw).
—HARDHEAD, Mylopharodon conocephalus. p. 14
8b. Upper lip without frenum.
9a. Mouth large, maxillary extending to just below anterior edge of the eye. Reaching length of 3 feet. Color plain.
—SACRAMENTO SQUAWFISH, Ptychocheilus grandis. p. 13
9b. Mouth small, maxillary not extending to eye. Not exceeding length of 5 inches. Color somewhat mottled.
—CHUB-ROACH, Hesperoleucus symmetricus. p. 14

1b. Ventral fins thoracic (attached immediately below the pectoral fins). Pectoral fins very large and thick. A small spine on preopercle (on side of head).
—RIFFLE SCULPIN, Cottus bairdii gulosus. p. 15