The effects of protein hydrolysates from rainbow trout by-products on growth, digestive and antioxidant enzymes, and liver lysozyme activity in sobaity (Sparidentex hasta) and Arabian yellowfin (Acanthopagrus arabicus) seabream juveniles

Abstract

An eight-week feeding trial was conducted to elucidate the effects of rainbow trout by-products protein hydrolysates (FPH, 92 % peptides <1 kDa, ∼78.1 % crude protein, ∼2.7 % lipid) on growth and some selected physiological responses in sobaity (Sparidentex hasta) (1.7 ± 0.0 g) and Arabian yellowfin (Acanthopagrus arabicus) (0.9 ± 0.0 g) seabream. Fish meal in a basal diet (∼58 % crude protein, ∼12 % lipid) was replaced with FPH at four levels, including 0 (control), 1 % (FPH1), 2.5 % (FPH2.5), and 5 % (FPH5). Each experimental diet was offered thrice daily to fish in triplicate. At the end of the feeding trial, S. hasta fed with FPH diets showed positive linear and quadratic trends in growth performance, and those fed with FPH5 had the highest final weight (FBW; 9.8 ± 0.4) and better feed conversion ratio (FCR; 0.9 ± 0.0). Regarding A. arabicus it showed positive quadratic trend and fish fed FPH2.5 diet had the highest FBW (6.2 ± 0.3), and better FCR (1.2 ± 0.0) value. Trypsin and alkaline phosphatase (ALP) activities showed both positive linear and quadratic trends in S. hasta. In A. arabicus, both linear and quadratic trends were observed in the activities of trypsin and total proteases (P = 0.001), while positive quadratic trends in pepsin and ALP activities were noticed. Lysozyme activity significantly increased by supplementing the diet with FPH and showed both linear and quadratic trends in S. hasta, but it did not change in A. arabicus. Total antioxidant capacity (TAC) in A. arabicus increased and showed both linear and quadratic responses. The catalase and glutathione peroxidase activities in both species increased significantly in response to dietary FPH. This study showed that FPH effects in diet were species-specific and its supplementation levels at 2.5 and 5 % could be recommended in A. arabicus and S. hasta juveniles, respectively.