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The present study aimed to investigate the ameliorative effects of lysolecithin on fish stearin oil, meanwhile comparing the application of two different forms (lysolecithin powder and lysolecithin oil) and three inclusion levels (0.25, 0.75, 1.25 g kg−1) in largemouth bass. The entire study consisted of a 28-day digestibility trial and a consequent 68-day feeding experiment. Eight iso-nitrogenous (∼ 500 g kg−1) and iso-energetic (∼ 22 MJ kg−1) diets with high lipid level (∼ 170 g kg−1) were formulated to contain the same level of two different types of lysolecithin, and namely WFO (130 g kg−1 winterized fish oil), FSO (130 g kg−1 fish stearin oil), LLP (FSO + 1 g kg−1 lysolecithin powder, purity 250 g kg−1), MLP (FSO + 3 g kg−1 lysolecithin powder), HLP (FSO + 5 g kg−1 lysolecithin powder), LLO (FSO + 0.625 g kg−1 lysolecithin oil, purity 400 g kg−1), MLO (FSO + 1.875 g kg−1 lysolecithin oil) and HLO (FSO + 3.125 g kg−1 lysolecithin oil), respectively. Largemouth bass fed FSO showed lower apparent digestibility coefficients (ADCs) of nutrients (total fat, crude protein, gross energy, total amino acid, total essential amino acid) than the WFO. Without considering the lysolecithin type, medium and high doses (0.75, 1.25 g kg−1) significantly increased ADCs of nutrients compared with the 0.25 g kg−1 supplementation level. Lysolecithin oil significantly increased ADCs of nutrients than the lysolecithin powder. Thus, lysolecithin oil was chosen for 68-day feeding trial, and results showed the highest FBW, FI, WGR and SGR were recorded in diet HLO, and significantly higher than the FSO, LLO and MLO. Diet MLO significantly decreased lipid and energy in whole-body and lipid retention compared with the FSO, LLO and HLO. In addition, activity and mRNA expression of adipose triglyceride lipase significantly increased, while glycerol-3-phosphate acyltransferase 4 decreased in diet HLO.

Coenzyme Q10 (CoQ10) is a powerful antioxidant that is gradually being used in aquafeeds. Here, we examined the influence of oxidized fish oil and CoQ10 supplementation on intestinal microbiota of Micropterus salmoides at different growth stages. Three isonitrogenous and isoenergetic diets were formulated to contain 100% fresh fish oil (FFO), 100% oxidized fish oil (OFO) and OFO + 0.1% CoQ10 (QFO) and were fed to Micropterus salmoides (95 ± 0.60 g) for 70 days. Furthermore, three different growth stages (28-day, 49-day, 70-day) were selected to observe the dynamic changes of intestinal microbiota. The growth performance of fish fed QFO were significantly higher than that of fish fed OFO after a 70-day’s feeding. Intestinal microbial community of Micropterus salmoides was significantly affected by different growth stages more than diets. The abundance of phylum Proteobacteria showed an increasing trend, while the abundance of Firmicutes decreased with increased feeding time. Compared with OFO, diet supplemented with CoQ10 significantly increased the abundance of Firmicutes, and decreased Proteobacteria on the 28- and 70-day of feeding. When fish fed OFO and QFO, Simpson and Shannon indices significantly increased with increased feeding time from 28 to 70 days. Fish fed QFO significantly decreased the value of Bray-Curtis distance than those fed FFO on the 70-day of feeding. Moreover, Bray-Curtis distance showed an increased trend with increased feeding time. Notably, intestinal microbial functional prediction indicated that OFO suppressed amino acid metabolism, while long-term oral administration of CoQ10 could improve amino acid metabolism and detoxification of Micropterus salmoides. This study demonstrated that prolonged application of CoQ10 is needed to produce some beneficial effects to Micropterus salmoides.

Somatic and expressional effects of replacing dietary fishmeal (FM) with a 1:1:2 combination of soy protein concentrate, corn gluten meal, and hydrolysate of forage-fish (HWF) or Pacific krill (HPK) were investigated in juvenile largemouth bass for 66 days. The control diet (FMC) contained 320 g kg−1of FM. Six extruded diets were produced with 3 rates of replacement at 25 %, 50 % and 75 % protein for each of the two hydrolysate combinations. Feed intake (FI) and weight gain (WGR) did not differ between fish fed HWF diets and FMC. Fish fed HPK50 and HPK75 had lower FI and WGR. FI linearly decreased with increasing HPK, while feed conversion ratio (FCR) increased. No significance was found in the FCR among groups fed FMC, HWF25, HWF50, and HPK25, whereas HWF75, HPK50, and HPK75 groups had significantly higher FCR. The apparent digestibility (AD) of crude protein (CP) increased with increasing HWF while HPK didn’t cause significant change. AD of lipid and energy were not affected by diet, and AD of most amino acids increased proportionally with HWF. No proximate composition or retention of crude or digestible protein or energy other than whole-body ash revealed HWF-related differences. Whole-body CP, lipid, ash contents and CP retentions showed significant dose response in HPK fed fish. The condition factor decreased linearly with increasing HPK. Fish fed HPK50 diet upregulated peptide transporter 1 (pept1) expression in the foregut. Expressions of both taurine transporter (taut) and pept1 were upregulated by increasing replacement from 0 % to 25 % HWF. Further increase in HWF replacement caused linear down regulation in expression of both transporters. In conclusion, HWF and HPK facilitated reduced use of fishmeal in practical diet for largemouth bass. Expressions of pept1 and taut were dose-dependent in fish fed HWF. HPK just caused single diet upregulation.