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Simple Summary: Aquafeed stored in hot, humid conditions can produce MDA, harming fish health. In a quest to uncover the negative impacts of dietary MDA on fish, we subjected hybrid grouper to a regimen of six experimental diets, each with a different MDA concentration, over an eight-week experimental period. It was found that diets with 4.43 mg/kg MDA lowered immune response, while 8.86 mg/kg increased inflammation. The highest MDA level (17.72 mg/kg) caused intestinal inflammation and damaged fish fillet texture. The study suggests a safety limit for MDA in grouper diets at 4.43 mg/kg, below which immune and fillet quality are minimally affected. However, higher levels harm gut health and fillet quality. Aquafeed kept at elevated temperatures and humidity can result in malondialdehyde (MDA) formation, adversely affecting aquafeed quality and triggering negative reactions in fish. To investigate the detrimental effects of dietary MDA on fish, six experimental diets with varying MDA levels (ranging from 0.03 to 17.72 mg/kg, on dietary crude lipid basis) were administered to three replicates of hybrid grouper for 8 weeks. Dietary inclusion of 4.43 mg/kg MDA significantly decreased serum complement 4 content and lysozyme activity, along with intestinal complement 3, complement 4, and immunoglobulin M contents. Furthermore, dietary inclusion of 8.86 mg/kg MDA significantly increased the activities of interleukin-1 receptor-associated kinase, ubiquitin-protein ligase, p38 mitogen-activated protein kinase, and tumor necrosis factor-α, downregulated the relative expression of Occludin but upregulated the relative expression of HSP70 in the hindgut. Additionally, the highest inclusion of MDA (17.72 mg/kg) significantly upregulated the relative levels of pro-inflammatory cytokines (IL-1β and TNF-α), caused intestinal inflammation, and damaged the intestinal microbial structure and fish fillet texture. This study demonstrated a dose-dependent response of MDA on hybrid grouper. A low dietary dose of MDA (<2.21 mg/kg) exhibited minimal impact on immune response and fillet quality. However, higher inclusion levels (≥4.43 mg/kg) impaired the intestinal health and fillet quality. Consequently, the safety limit for MDA content in the diet for hybrid grouper has been established at 4.43 mg/kg based on dietary crude lipid basis. [ABSTRACT FROM AUTHOR]

Spotlighting the current state of largemouth bass (Micropterus salmoides) aquaculture, this study exhibited the effects of steroidal saponins (SS) on the liver health of largemouth bass under high‐temperature stress. The study consisted of two experiments: the first trial was designed to evaluate the growth performance of fish fed the experimental diets containing SS 0% and 0.1% (SS0 and SS0.1) for 30 days. And then, the second trial was used to evaluate the health of the livers of these fish under high‐temperature (34°C) stress which lasts for 1 week, and the groups were named as SS0, HSS0, SS0.1, and HSS0.1, respectively. In the first feeding trial, except for the higher feeding rate observed in the SS0.1 group (P < 0.05), no significant difference was observed between the groups SS0 and SS0.1 in survival rate, weight gain rate, specific growth rate, and feed conversion rate, respectively. After 1 week of high‐temperature stress, the specific growth rate and weight gain rate of fish were significantly lowered in the HSS0 and HSS0.1 groups (P < 0.05). In terms of feeding rate, the SS0.1 and HSS0.1 groups were significantly higher than the other two groups (P < 0.05). Under high‐temperature stress, gene expressions of caspase-3, caspase-8, caspase-9, tnf-α, il-8, and hsp70 were significantly downregulated in the liver of largemouth bass in the HSS0.1 group (P < 0.05). The activities of antioxidant enzymes, including catalase, total superoxide dismutase, and glutathione peroxidase in the liver, were significantly increased, while the serum enzyme activities of aspartate aminotransferase and alanine aminotransferase were significantly decreased in the HSS0.1 group (P < 0.05). Compared to the HSS0 group, hepatic vacuolization areas of fish in the HSS0.1 group were improved (P < 0.05). Therefore, the results of the study supported that the 0.1% SS used in largemouth bass diet for 30 days could strengthen the liver and body health and help fish resist heat stress. [ABSTRACT FROM AUTHOR]

This study investigated the effect of adding the compound acidifiers on the intestine health of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed diet with higher cottonseed protein concentrate (CPC). To assess the benefits of compound acidifiers helping CPC to replace more fish meal (FM) for hybrid grouper, five isonitrogen and isolipid experimental diets were formulated. The five diets consisted of a control diet (FM, 50%) and four experimental diets (27.5% FM, 27.27% CPC), each of which contained compound acidifiers to varying degrees (FCA0, FCA0.05, FCA0.1, and FCA0.2). Each diet was fed to three replicates of each group for 8 weeks. In the FCA0.05 group, the results demonstrated a statistically significant increase in protein efficiency ratio, lipid efficiency ratio, and the activity of digestive enzymes in the intestine (P < 0.05). In the FCA0.05 group, there was a clearly enhanced expression of anti‐inflammatory cytokines in the intestines (P < 0.05). In the FCA0.1 group, there may be an increase in the expression of important genes involved in fatty acid metabolism in the intestinal (P < 0.05). Appropriate compound acidifiers decreased the relative abundance of Vibrio and other harmful bacteria in the intestine flora that were brought by high CPC. In conclusion, when the hybrid grouper was given a diet containing more CPC, the FCA0.05 group was able to promote intestinal development, enhance digestive enzyme activity and feed consumption, raise antioxidant enzyme activity and anti‐inflammatory factor expression, and improve intestinal health. [ABSTRACT FROM AUTHOR]