RESUMO
Three experiments were performed to explore (i) the complete replacement of fish meal (FM) with a combination of fish residue meal (FRM, 65% round discarded fish + 35% byproduct), soy protein concentrate (SPC) from soymilk and corn gluten meal (CGM) in Trial 1 and (ii) the utilization of diets composed of increasing byproducts in FRM in the summer (Trial 2) and winter (Trial 3) seasons. In Trial 1, the ratio of (SPC + CGM):FM in the control diet (C) was 8:2. The FM component from diet C was replaced with FRM (diet, RM20), where the ratio of (SPC + CGM):FRM became 8:2, and this ratio was changed to 6:4, 4:6 and 2:8, and referred to as RM40, RM60 and RM80, respectively. In Trials 2 and 3, the ratios of round discarded fish and byproducts in FRM were adjusted to 65:35 (FRM1), 30:70 (FRM2) and 0:100 (FRM3), and the FRM component from diet RM40 in Trial 1 was replaced with FRM1, FRM2 and FRM3 to formulate diets RM1, RM2 and RM3, respectively. In Trials 1, 2 and 3, rearing periods were 10, 8 and 12 weeks, respectively. In Trials 1 and 3, there were no significant differences in growth parameters, nutrient retention efficiency or plasma constituents among the treatments, irrespective of the inclusion levels of FRM in the diets (p > 0.05). Although there were no significant differences in final mean weight (p > 0.05), daily feeding rate and feed conversion ratio in diet RM3 were significantly higher and lower, respectively, compared to the control group in Trial 2 (p < 0.05). These results suggest that FM can be entirely replaced with FRM, and that the total elimination of round discarded fish from FRM does not affect growth or health status in red sea bream either in summer or winter seasons.
RESUMO
To reveal direct effects of various protein sources on digestive physiology of red seabream, Pagrus major (38.5 ± 0.4 g), six different protein sources of fishmeal (FM), soybean meal (SBM), corn gluten meal (CGM), soy protein concentrate (SPC), poultry by-product meal (PBM), and poultry-feather meal (PFM) were orally administered to fish (2 mg protein/g body weight) and sampled at 1.5 h and 3 h after administration. Gallbladder weight of fish administered FM, PBM, and PFM decreased after administration (p < 0.0001), while no difference was observed in the other ingredients compared to a non-protein sham control group, indicating that animal protein sources could more strongly stimulate bile secretion than plant protein sources in red seabream. Trypsin and chymotrypsin activity in the intestinal content markedly increased by the FM, SBM, and PFM administration (p < 0.0001). Lipase and amylase activity was also increased by FM and SBM but also by CGM for lipase and by PBM and PFM for amylase (p < 0.0001). These indicate that stimulation effect of the secretion of digestive enzymes is largely different among the protein sources. This might be due to the absorptive capacity of the protein source since intestinal absorption parameter genes (anpep, cpa, ggt1, and atp1a2) also increased by the FM, SBM, PBM or PFM (p < 0.05). In addition to the secretion levels of bile and digestive enzymes, gene expression levels of bile related genes (cyp7a1, cyp8b1, and shp) and digestion-regulating genes (casr and cck) were increased by the FM, SBM, PFM, and/or PBM administration, suggesting that animal proteins and SBM could be potent digestive stimulants compared to CGM and SPC. This study first revealed that single protein sources directly influence digestive enzyme secretion and bile secretion in fish. Information about the direct effect of each single source on digestive physiology could help to design feed formulation with less fishmeal.