Fin Condition and Health Profiles of Albino Rainbow Trout Reared in Concrete Raceways with and without a Cobble Substrate

Fingerlings of albino rainbow trout Oncorhynchus mykiss were reared for 200 d in concrete raceways with either concrete (controls) or cobblestone bottoms. Health and condition profiles were performed on 20 fish/treatment on four occasions. For fish in cobble‐bottom raceways, there was no fin erosion as measured by fin indices (ranked from 0 to 2) applied to the fish as a whole or relative fin lengths (% of body length) of individual fins. For control fish, however, considerable erosion was evident for caudal, dorsal, anal, both pectoral, and both ventral fins. Condition factor, fat levels, and total length were reduced in cobbled raceways. Results are compared with previous experiments with normally pigmented rainbow and cutthroat trout O. clarki. Overall, cobble substrates markedly reduced fin erosion, which suggests that cobble‐bottom raceways are especially suitable for rearing albino rainbow trout, if a slight reduction in growth is acceptable.