Histidine requirement of rainbow trout ( Oncorhynchus mykiss ) fed a low fishmeal‐based diet for maximum growth and protein retention

Abstract

A two-phase feeding trial was conducted to estimate the dietary histidine requirement of juvenile and post-juvenile rainbow trout for maximum growth and protein retention. Twelve isonitrogenous experimental diets were formulated where diet 1 was an 8% fishmeal basal diet having 0.5% histidine. Histidine was added to diets 2–6 to achieve levels of 0.7, 0.9, 1.1, 1.3 and 1.5% histidine respectively. Diets 7–12 were identical to diets 1–6 except for pellet size. In trial 1, fish (4 g) were fed test diets 1–6, and in trial 2, fish (40 g) were fed diets 7–12, to four replicate tanks per diet for 12 weeks. A nutrient digestibility trial was also conducted with trout from trial 2. Growth performance and feed utilization were not significantly influenced by dietary histidine supplementation above the basal diet level in either rainbow trout juveniles or post-juveniles. Supplementation of histidine significantly increased protein and histidine digestibility, and it was lowest in the basal diet group. The highest histidine retention was in the lowest dietary histidine treatment group, and histidine retention progressively decreased at each increase in dietary histidine. In post-juvenile trout, the same pattern was observed except that for the two lowest histidine levels, retention was similar and high. Finally, considering the overall growth and nutrient retention performances, the dietary histidine requirement is relatively higher in post-juvenile trout (>0.6%) rather than juvenile trout (0.6%) under the present experimental conditions.