An 8-week feeding trial was performed to examine the potential of total replacement of fish meal with animal by-products with or without enzymatic components in juvenile genetically improved farmed tilapia (GIFT) diets,Oreochromis niloticus, (mean initial weight, 19.71 +/- 0.28 g), reared in RAS system. Five isonitrogenous and isoenergetic diets were formulated with fish meal for the diets with total replacement of the isonitrogenous amounts of enzymatic fish meal (E-FM), chicken liver meal (CLM), enzymatic chicken liver meal (E-CLM), dried porcine solubles (DPS) and enzymatic dried porcine solubles (E-DPS) respectively. The results indicated that the weight gain rate (WGR) and specific growth rate (SGR) in the FM group were significantly higher than the E-FM and E-CLM groups (p< .05), but the specific growth rate (SGR) in the E-CLM group lower than the E-FM group. The feed conversion ratio (FCR) in FM and CLM was significantly lower than the E-FM, E-CLM and E-DPS groups (p < .05), and no significant difference was observed among the FM, CLM and DPS groups (p > .05). The values of the protein retention efficiency (PRE) and protein efficiency ratio (PER) in FM, CLM and DPS groups were significantly higher than the E-CLM group (p < .05). The values of feed intake ratio (FIR) in FM and CLM groups were significantly lower than the E-FM, E-CLM and E-DPS groups (p < .05). There was no significant difference in the whole body contents of moisture, crude lipid and crude ash among the FM and E-CLM groups (p > .05). The whole body contents of crude protein in the FM group were significantly higher than the E-FM, CLM, E-CLM DPS and E-DPS groups (p < .05). The apparent digestibility coefficients (ADC) of dry matter, crude protein and crude lipid in the FM, E-FM, E-CLM and E-DPS groups were not significantly different (p > .05). The serum glucose(GLU), total cholesterol (TCHO) and triglycerides (TG), or the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were not affected by the different treatments (p > .05). There was no significant difference in serum total protein (TP) or albumin (ALB) and between the FM group and other groups (p > .05). There was no significant difference in the serum urea nitrogen (BUN) content in the FM, CLM, E-CLM and DPS groups (p > .05). Fish fed with the CLM and DPS diets had significantly lower hepatic GHR1, IGF1 and IGF2 gene mRNA expression levels than in fish fed the FM diet (p < .05). The present data showed that 6% of dietary fish meal can be totally replaced by the chicken liver meal and dried porcine solubles with no effect on the growth performance of GIFT strain tilapia.

DHA and EPA, as indispensable n-3 highly unsaturated fatty acids (HUFAs), exert a fundamental influence on regulating fish growth, lipid metabolism, and overall well-being. However, there is a notable lack of data concerning their effects on the F2 female generation of Yangtze sturgeon. Over a ten-month period, this study assessed the impacts of various dietary concentrations of n-3 HUFAs (0.5%, 1.0%, 1.5%, 2.0%, and 2.4%) on growth, fatty acid composition, lipid metabolism, inflammatory response, and intestinal microbiota in the F2 female generation of Yangtze sturgeon. Seventy-five test fish, with an average body weight of 3.60 ± 0.83 kg, were housed in 15 ponds, with each dietary group being assigned to three ponds. The results indicated that the 1.0%~1.5% n-3 HUFA group was characterized by the highest values of weight gain rate; serum triglyceride levels peaked in the 0.5% n-3 HUFA group. The fatty acid profiles of the fish tissues closely mirrored those of the diets. Specifically, compared to the 1.5% and 2.0% n-3 HUFA groups, the diet containing 2.4% n-3 HUFA down-regulated the mRNA expression of transforming growth factor beta, and, compared to the 0.5% and 1.0% n-3 HUFA groups, the 2.0% n-3 HUFA diet up-regulated the mRNA expression of nuclear factor kappa B. Conversely, compared to the 0.5% n-3 HUFA group, 2.0% n-3 HUFA in the diet up-regulated the gene mRNA expression of fatty acid binding protein 1 and fatty acid synthase. Compared to the 0.5% n-3 HUFA group, 1.0% n-3 HUFA in the diet up-regulated the gene mRNA expression of lipoprotein lipase. The α-diversity indices (ACE, PD_whole tree, Richness, and Chao1) exhibited an upward trend with increasing dietary n-3 HUFA levels, and the 2.4% n-3 HUFA group reached the highest values. At the phylum level, Fusobacteriota, Proteobacteria, Firmicutes, and Bacteroidota were the primary dominant phyla. Cetobacterium was the dominant genus in all groups. Collectively, these findings underscore that moderate dietary supplementation of n-3 HUFA (1.3%) is optimal and does not impair growth. The deposition of fatty acids in muscle and ovarian tissues, as well as the mRNA expression of lipid-metabolism genes, are closely associated with the dietary n-3 HUFA content. High levels of n-3 HUFA did not suppress intestinal α-diversity. These discoveries provide novel insights into the regulation of growth, lipid metabolism, and health in the F2 female generation of Yangtze sturgeon and offer a nutritional strategy for the artificial conservation of this endangered species.

Sturgeon is known as a primitive fish with the ZZ/ZW sex determination system and is highly prized for its valuable caviar. Exploring the molecular mechanisms underlying gonadal differentiation would contribute to broadening our knowledge on the genetic regulation of sex differentiation of fish, enabling improved artificial breeding and management of sturgeons. However, the mechanisms are still poorly understood in sturgeons. This study aimed to profile expression patterns between female and male gonads at morphologically undifferentiated and early differentiated stages and identify vital genes involved in gonadal sex differentiation of sturgeons. The sexes of Yangtze sturgeon (Acipenser dabryanus) juveniles were identified via the sex-specific DNA marker and histological observation. Transcriptome analyses were carried out on female and male gonads at 30, 80 and 180 days post-hatching. The results showed that there was a total of 17 overlapped DEGs in the comparison groups of between female and male gonads at the three developmental stages, in which there were three DEGs related to ovarian steroidogenesis, including hsd17b1, foxl2 and cyp19a1. The three DEGs were highly expressed in the female gonads, of which the expression levels were gradually increased with the number of days after hatching. No well-known testis-related genes were found in the overlapped DEGs. Additionally, the expression levels of hsd17b1 and cyp19a1 mRNA were decreased with the knockdown of foxl2 mRNA via siRNA. The results further suggested that foxl2 should play a crucial role in the ovarian differentiation of sturgeons. In conclusion, this study showed that more genes involved in ovarian development than testis development emerged with sexually dimorphic expression during early gonadal sex differentiation, and it provided a preliminary understanding of the molecular regulation on gonadal differentiation of sturgeons.

Currently, the effects of dietary levels of n-3 highly unsaturated fatty acids (HUFAs) on the growth performance, antioxidant capacity, immunity, and serum oxylipin profiles of female F₂-generation Yangtze sturgeon remain unknown. A total of 75 Yangtze sturgeons, an endangered freshwater fish species, with an average body weight of 3.60 ± 0.83 kg, were randomly allocated to 15 concrete pools, with each dietary group represented by 5 fish per pool. The fish were fed five different experimental diets containing various levels of n-3 HUFAs (0.5%, 1.0%, 1.5%, 2.0%, and 2.4%). After a feeding period of 5 months, no significant differences in the growth performances of the fish were observed among the five dietary groups (p > 0.05). However, we did note that the serum levels of low-density lipoprotein cholesterol (LDL-C), triglycerides (TGs), and total cholesterol (TCHO) exhibited a marked increase in the fish that consumed higher dietary n-3 HUFA levels (p < 0.05). Conversely, alkaline phosphatase (ALP) activities showed a notable decrease as dietary n-3 HUFA levels increased (p < 0.05). Serum antioxidant indices, such as the activity levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), were significantly higher in the 2.4% HUFA group compared to the 0.5% HUFA group. Additionally, muscle antioxidant indices, including total antioxidant capacity (T-AOC), catalase (CAT), and SOD activity, exhibited notable increases as dietary n-3 HUFA levels increased (p < 0.05). Furthermore, there was a decrease in malondialdehyde (MDA) levels as dietary n-3 HUFA levels increased (p < 0.05). In relation to immune indices, only serum immunoglobulin M (IgM) and muscle complement 3 (C3) were found to be influenced by dietary n-3 HUFA levels (p < 0.05). A total of 80 oxylipins were quantified, and our subsequent K-means cluster analysis resulted in the classification of 62 oxylipins into 10 subclasses. Among the different n-3 HUFA diets, a total of 14 differential oxylipins were identified in the sera. These findings demonstrate that dietary supplementation with n-3 HUFAs exceeding a 1.0% level can enhance antioxidant capacity and regulate serum lipid metabolism, potentially through modulation of oxylipins derived from ARA, DHA, and EPA. These insights provide novel perspectives on the mechanisms underlying these observations.