Common carp
Leidy (2007) identified the native fishes in San Tomas Aquino Creek as Hitch ("Lavinia exilicauda"), California roach ("Lavinia symmetricus"), Sacramento sucker ("Catostomus occidentalis occidentalis"), Three-spined stickleback ("Gasterosteus aculeatus"), rainbow trout ("Oncohrynchus mykiss irideus") and possibly Chinook salmon ("Oncorhynchus tshawytscha"). Although the latter had been considered now absent from the watershed, in mid-October, 1996, Roger Castillo, the founder of the Salmon and Steelhead Restoration Group, recovered a giant Chinook salmon from San Tomas Aquino Creek beneath Highway 237 (see photo). Non-native fishes include Common carp ("Cyprinus carpio"), Goldfish ("Carassius auratus auratus"), Golden shiner ("Notemigonus crysoleucas"), and Western mosquitofish ("Gambusia affinis").