The optimal dietary protein and lipid levels for juvenile hybrid sunfish ( lepomis cyanellus ♀ × Lepomis macrochirus ♂)

Abstract

An eight-week feeding trial was conducted to examine the optimal dietary protein and lipid levels for juvenile hybrid sunfish (Lepomis cyanellus ♀ × Lepomis macrochirus ♂). A 5 × 2 factorial layout containing five protein levels (300, 340, 380, 420 and 460 g kg−1) and two lipid levels (30 and 80 g kg−1) was designed. Fish (initial body weight 1.21 ± 0.06 g) were fed the test diets twice daily. The final body weight (FBW) and per cent weight gain (PWG) in fish increased with dietary protein level from 300 to 420 g kg−1, and afterwards decreased with dietary protein level from 420 to 460 g kg−1. Feed intake and feed conversion ratio (FCR) significantly declined with increase dietary protein level. Fish fed at 380 and 420 g kg−1 dietary protein level exhibited higher nitrogen retention efficiency (NRE) and phosphorus retention efficiency (PRE), however, lower nitrogen and phosphorus wastes, than in fish fed at 300 g kg−1 dietary protein level. For different dietary lipid levels, the higher FBW, PWG, NRE and PRE, but the lower feed intake, FCR, nitrogen and phosphorus wastes, were found in fish fed at 80 g kg−1 dietary lipid level than those in fish fed at 30 g kg−1 dietary lipid level. At the end of feeding trail, the contents of body moisture and lipid were significantly influenced by dietary lipid level. According to these results, a diet containing 420 g kg−1 protein and 80 g kg−1 lipid is recommended for efficient growth of juvenile hybrid sunfish.