Comparative study on dietary protein requirements for juvenile and pre-adult gibel carp ( Carassius auratus gibelio var. CAS III).

Two 8-week growth trials were conducted in indoor recirculation system to evaluate the protein requirements for juvenile (3.70 ± 0.20 g) and pre-adult (85.2 ± 0.70 g) gibel carp, Carassius auratus gibelio var. CAS III. Six isoenergetic diets were formulated for each trial using fish meal and casein as protein sources, and protein level was 250-450 g kg−1 in Trial 1 and 200-450 g kg−1 in Trial 2. With the increasing dietary protein, feeding rate ( FR) and feed conversion ratio ( FCR) significantly decreased ( P < 0.05). Weight gain ( WG) increased first and then reached a plateau in 330-450 g kg−1 in Trial 1 ( P > 0.05), while decreased after the maximum value in 350 g kg−1 in Trial 2 ( P < 0.05). Productive protein values ( PPVs) were lower in 370-450 g kg−1 in Trial 1 and 400-450 g kg−1 in Trial 2 ( P < 0.05). Increasing dietary protein level increased protein content and decreased lipid content in whole fish body and white muscle ( P < 0.05). Apparent digestibility coefficient of dry matters ( ADCd) decreased, while apparent digestibility coefficient of protein ( ADCp) increased in 370-450 g kg−1 in Trial 1 and 250-450 g kg−1 in Trial 2 ( P < 0.05). Trypsin activity significantly increased in 370-450 g kg−1 in Trial 1 ( P < 0.05) and was not affected in Trial 2 ( P > 0.05). Hepatic alanine aminotransferase ( ALT) and aspartate aminotransferase ( AST) activities in both trials increased when dietary protein was above 400 g kg−1 ( P < 0.05). Based on quadratic regression of WG, it was estimated that dietary protein requirement for maximum growth was 414 g kg−1 (digestible protein of 376 g kg−1) and 365 g kg−1 (digestible protein of 324 g kg−1) for juvenile (3.70 g) and pre-adult gibel carp (85.2 g). [ABSTRACT FROM AUTHOR]