Replacement of dietary fishmeal by cottonseed protein concentrate on growth performance, feed utilization and protein metabolism of large yellow croaker Larimichthys crocea

A 90-day feeding trial was conducted to evaluate the effects of cottonseed protein concentrate (CPC) replacing dietary fishmeal on growth performance, feed utilization and protein metabolism of large yellow croaker (initial body weight: 191.60 ± 1.36 g). Seven iso-nitrogenous and iso-lipidic experimental diets were formulated by replacing 0%, 15%, 30%, 45%, 60%, 75% and 100% of dietary fishmeal with CPC. The experimental diets were named as CPC0, CPC15, CPC30, CPC45, CPC60, CPC75 and CPC100, respectively. Results showed that when CPC replacement level was less than 60%, there were no significant differences in survival, weight gain rate, feed intake, feed conversion ratio, protein efficiency ratio, hepatosomatic index, visceral somatic index and condition factor of large yellow croaker compared with those in the CPC0 group (P > 0.05). The dorsal muscle proximate compositions and amino acid profiles were not significantly affected by dietary CPC replacement levels (P > 0.05). Compared with those in the control group, digestive and absorptive enzymes activities in the intestine and liver in the CPC75 and CPC100 groups decreased significantly (P < 0.05). The perimeter ratio, muscularis thickness and villus height in the intestine decreased linearly with increasing replacement levels of dietary fishmeal by CPC (P < 0.05). Compared with those in the CPC0 group, the mRNA levels of mammalian target of rapamycin, ribosomal protein S6, eukaryotic translation initiation factor 4E in the muscle were down-regulated with increasing dietary CPC levels, and while the expressions of eukaryotic translation initiation factor 4E-binding protein, general amino acid control nonderepressible 2 and eukaryotic translation initiation factor 2 α were up-regulated. Take the growth performance, feed utilization and protein metabolism into account, 60% of dietary fishmeal could be replaced by CPC in large yellow croaker.