Growth Performance, Tissue Fatty Acid Composition, and Consumer Appeal of Rainbow Trout Reared on Feeds Containing Terrestrially Derived Rendered Fats

We evaluated the growth, fillet fatty acid composition and consumer appeal of rainbow trout Oncorhynchus mykiss raised on feeds containing fish oil or blends of fish oil and terrestrially derived rendered fats. The fish (128 ± 2 g, mean ± SE) were stocked in a recirculation system (eight fish/tank) and fed a fish‐oil‐based feed or feeds containing 50/50 blends of fish oil and beef tallow, pork lard, poultry fat, or restaurant grease exclusively (18 weeks) or in combination with a finishing feed (10 weeks grow out + 8 weeks finishing). Survival (94 ± 2%, mean ± SE), weight gain (384 ± 11%), specific growth rate (1.14 ± 0.02% body weight/d), feed conversion ratio (1.57 ± 0.03), cumulative individual consumption (755 ± 13 g), and feed intake (1.97 ± 0.03% body weight/d) were equivalent among the feeding regimens. The fillet fatty acid composition changed during grow out to more closely resemble the composition of the rendered‐fat‐based feeds, but at harvest the fillets were quite similar across all regimens. The results of the taste test showed that participants were able to correctly identify differences between the fillets of fish fed the experimental feeds and those fed the fish‐oil‐based feed exclusively in only 36% of comparisons, and the participants showed no obvious preference for fillets from any regimen. Beef tallow, pork lard, poultry fat, and restaurant grease may be used to spare fish oil in diets for rainbow trout without grossly impacting production performance or the sensory or nutritional quality of the resultant fillets. Finishing with a fish‐oil‐based feed may correct minor differences in fillet fatty acid composition; however, finishing may not be necessary to achieve a desirable fillet profile. Significant cost savings may be realized through implementation of rendered fats as fish oil alternatives in rainbow trout feeds.