Effects of feeding levels on growth performance, feed utilization, body composition, energy and protein maintenance requirement of fingerling, rainbow trout, Oncorhynchus mykiss (Walbaum ۱۷۹۲)

A ۱۰-week feeding experiment was conducted to evaluate the effects of feeding level, energy and protein maintenance requirement of rainbow trout, Oncorhynchus mykiss, fingerling (۵.۶۵±۰.۴۵cm; ۱.۴۲±۰.۲۵g) by feeding casein-gelatin based purified diet (۴۵% CP; ۳.۶۷ kcal g-۱ GE) at six feeding levels from ۲ to ۷% of BW/day in two equal meals, at ۰۸۰۰ and ۱۷۰۰ h, in triplicate, with ۲۰ fish per trough equipped with continuous water flow-through system water (۶۰L volume). Maximum live weight gain, best feed conversion ratio (FCR), best specific growth rate (SGR) and highest protein efficiency ratio (PER) were reported in fish fed ۴-۵% BW day-۱. However, quadratic regression analysis for weight gain, FCR, PER, protein retention efficiency and energy retention efficiency data indicated the break-points occurred at ۵.۳۳, ۴.۵۰, ۴.۴۸, ۴.۶۳ and ۴.۷۴% BW day-۱, respectively. Body composition also produced significant (p<۰.۰۵) differences with respect to each feeding level, maximum protein, lowest moisture and intermediate fat contents were reported at ۴-۵% feeding levels. Protein and energy retention values also produced significant (p<۰.۰۵) differences among each feeding level with maximum values were reported at ۵% feeding level. Based on the results, it is recommended that feeding in the range of ۴.۶ to ۵.۳% BW day-۱, corresponding to ۲.۰۷-۲.۳۹g protein and ۱۶.۸۸-۱۹.۴۵ kcal energy g۱۰۰g-۱ of the diet day-۱ is optimum for the growth and efficient feed utilization of rainbow trout, while ۲-۳% feeding levels (۰.۹۰-۱.۳۵g protein and ۷.۳۴-۱۱.۰۱ kcal energy) suggests that these amounts approximate the maintenance requirement of fish.

Keywords:

Oncorhynchus mykiss , Feeding rate , Growth performance , Maintenance requirement