GROWTH OF JUVENILE SNAKE RIVER CUTTHROAT TROUT (Oncorhynchus clarkii behnkei) FED COMMERCIAL-TYPE DIETS

Cutthroat trout (Oncorhynchus clarkii) are raised for restoration stocking and to provide boutique sportfishing opportunities. Because of limited cutthroat-specific culture information, cutthroat trout have been raised under conditions developed for rainbow trout (O. mykiss), often resulting in inconsistent growth performance and survival. The purpose of this study was to identify what type of commercially available diet formulations will optimize growth rates in cutthroat trout.

A 6-month feeding trial was conducted in a partial recirculating system on juvenile Snake River cutthroat trout (O. c. behnkei) fed six different feed formulations. Two controls were chosen for this study (Skretting Classic Trout and Skretting Steelhead), along with three commercial-type (CT) formulations with varying crude protein (CP) and crude lipid (CL) levels (40 CP:12CL, 45CP:16CL, and 45CP:24CL) and one experimental formulation (40CP:16CL diet with lysine, methionine and threonine balanced to match the 45CP:16CL diet - BFTC Experimental).

Diet significantly (P<0.05) affected final average fish weight and specific growth rate (Table 1). Fish fed Skretting Steelhead and CT 45:24 weighed significantly more than fish fed CT 40:12 and had significantly higher SGRs than fish fed CT 40:12.

Proximate composition was also altered by diet, with significant differences in whole body moisture and crude energy. Fish fed CT 45:24 had significantly higher crude energy levels (1895 cal/g)  than fish fed CT 40:12 (1664 cal/g) and Skretting Classic Trout (1638 cal/g). Additionally, fish fed CT 45:24 had significantly lower percent moisture (69.0%) than fish fed  CT 40:12 (71.6%).  Overall, the results indicate that the most nutrient dense diets provide the greatest growth in juvenile Snake River cutthroat trout.