Utilization of thin distillers' solubles as a palatability enhancer in rainbow trout (Oncorhynchus mykiss) diets containing canola meal or air-classified pea protein

Two short‐term palatability experiments indicated that supplementation of diets containing 15.0% of canola meal or 30.5% of air‐classified pea protein with 3.3% or 3.9% thin distillers' solubles (dry matter basis), respectively, increased feed intake (P < 0.05) of rainbow trout over a 4‐day period. Supplementation of the same diets with 6.6% or 1.9% thin distillers' solubles, respectively, did not increase feed intake (P > 0.05). Supplementation of the diets with 1.0% of a commercial palatability enhancer did not increase feed intake (P > 0.05). A subsequent 12‐week growth experiment evaluated the long‐term feed intake enhancing capability of thin distillers' solubles. Supplementation of diets containing 20.0% of air‐classified pea protein or 20.0% of canola meal fines with thin distillers' solubles (4.0%, dry matter basis) over a 12‐week period had no effect on feed intake or growth of rainbow trout fed either diet (P > 0.05). The reduction in the palatability enhancing ability of thin distillers' solubles may be the result of the fish becoming accustomed to the taste of this product over a longer feeding period, or because of the possible destruction or alteration of the amino acids involved in gustatory stimulation during thermal processing.