The present study investigated the effects of dietary lactic acid (LA) supplementation on the growth performance, intestinal digestive/antioxidant enzymes’ activities, gene expression, and bacterial communities in common carp, Cyprinus carpio. Four diets were formulated to contain 0 g/kg LA (control), at 2.5 g/kg LA (2.5LAC), 5 g/kg LA (5LAC), and 10 g/kg LA (10LAC) and offered to the fish over a period of 56 days. The results showed that dietary 5 g/kg LA supplementation improved growth performance and feed efficiency in the fish. All LA treatments exhibited significant elevations in the intestinal trypsin and chymotrypsin activities, whereas the intestinal lipase, amylase, and alkaline phosphatase activities exhibited significant elevations in the 5LAC and 10LAC treatments. All LA treatments exhibited significant elevations in the intestinal heat shock protein 70, tumor necrosis factor-alpha, interleukin-1 beta, and defensin gene expressions, and the highest expression was observed in the 5LAC treatment. Additionally, dietary LA treatment significantly increased the lysozyme expression and Lactobacillus sp. population in the intestine of the fish, and the highest values were observed in the 5LAC and 10LAC treatments. Aeromonas sp. and Vibrio sp. populations decreased in the LA treatments, and the lowest Aeromonas sp. population was observed in the 10LAC treatment. The intestinal mucin2 and mucin5 expressions, and the hepatic reduced glutathione content, significantly increased, whereas hepatic glutathione peroxidase, glutathione reductase, and malondialdehyde significantly decreased in the 5LAC and 10LAC treatments. In conclusion, dietary 5 g/kg LA is recommended for common carp feeding to improve growth rate, antioxidant capacity, and intestinal health.

Tartaric acid (TA) is an organic acid whose properties in aquaculture have not yet been comprehensively studied. In the current research, the effect of dietary TA on growth indices, gut microbiota, the level of digestive enzymes, antioxidant and immunological markers, and survival rate following immersion challenge with Vibrio parahaemolyticus (14 days) in Litopenaeus vannamei were investigated. To achieve this, 600 shrimp (3.26 ± 0.05 g) were tested with pellets supplemented with five distinct concentrations of TA including 0 (TA0), 2.5 (TA2.5), 5 (TA5), 7.5 (TA7.5), and 10 g/kg (TA10) for 56 days. The results showed that the growth performance, feed utilization, gut lactic acid bacteria (LAB) count, and activity of digestive enzymes were markedly elevated in the groups receiving diets incorporated with 5 and 7.5 g/kg of TA. The highest total hemocyte count (THC), hyaline cell (HC), and semi-granular cell (SGC) counts were detected in shrimp fed with the TA7.5 diet. Hemolymph immune responses including LYZ (lysozyme), alkaline phosphatase (AKP), acid phosphatase (ACP), and phenol oxidase (PO) activities were significantly enhanced in all TA-treated groups. Dietary TA7.5 significantly boosted all antioxidant enzymes. In addition, malondialdehyde (MDA) content illustrated a significant decrease in shrimp fed with diets supplemented with 2.5–10 g/kg TA when compared with specimens fed with TA0. The survival rate following the immersion challenge with Vibrio parahaemolyticus markedly increased in all shrimp treated with 2.5–10 g/kg TA compared to TA0, irrespective of the dosage. However, the dietary inclusion of TA7.5 resulted in the highest survival rate. Based on the outcomes, dietary TA, especially at the concentration of 7.5 g/kg, is proposed to promote the growth performance and immunological indicators of L. vannamei.

This study aimed to evaluate the effects of dietary 1,8‐cineole (CIN) on Nile tilapia, Oreochromis niloticus , reared at different stocking densities. Fish (average initial weight 13.2 ± 0.35 g) were fed diets supplemented with 0%, 0.25%, or 0.5% CIN and stocked at either 14 (normal) or 56 (high) fish per 120‐L tank. The fish were reared for 8 weeks in triplicate and fed the diets at a rate of 4% per day. The results showed no significant interaction effects between dietary CIN and stocking density for any of the parameters tested. Also, there were no significant differences between 0.25% and 0.5% CIN treatments in any tested parameters. Dietary CIN and stocking density had no significant effects on feed efficiency and fish growth rate, plasma cortisol, and glucose levels. Dietary CIN significantly increased the plasma total antioxidant capacity and hepatic superoxide dismutase activity, but decreased hepatic malondialdehyde levels. The increase in fish stocking density significantly increased the plasma total antioxidant capacity and hepatic malondialdehyde levels. Dietary CIN and stocking density had no significant effect on the hepatic catalase activity. Dietary CIN significantly increased skin mucus alkaline phosphatase and plasma alternative complement activities, but fish stocking density had no significant effect on these parameters. Dietary CIN significantly increased lysozyme activities and immunoglobulin levels in plasma, skin mucus, liver, and kidney. The increase in fish stocking density significantly decreased lysozyme activities in plasma, skin mucus, and liver, but increased the kidney lysozyme activity. Moreover, the increase in fish stocking density significantly increased immunoglobulin levels in the liver and skin mucus, but decreased them in the plasma. In conclusion, this study demonstrates that an increase in stocking density up to 56 fish per 120‐L tank had no detrimental effect on feed efficiency and growth performance of Nile tilapia. Also, dietary CIN does not affect Nile tilapia growth but boosts antioxidant and immune systems, which may improve fish welfare and resilience. Hence, dietary 0.25% CIN supplementation is recommended for Nile tilapia feed formulation.

This study evaluated the effects of dietary inclusion of fermented sesame oilcake (FSOC) on growth performance, antioxidant responses, immune parameters, bactericidal activity, and gut microbial composition in juvenile Nile tilapia, Oreochromis niloticus . FSOC was produced by aerobic solid‐state fermentation using Saccharomyces cerevisiae . Fish (5‐month‐old, 13.31 ± 0.73 g, all‐male) were randomly distributed into three treatment groups and fed diets containing 0% (control [CTL]), 10% (S‐10), or 20% (S‐20) FSOC for 8 weeks. Growth performance, feed conversion ratio, and survival were not significantly affected by FSOC inclusion ( p > 0.05). However, dietary FSOC significantly enhanced several immunological parameters, including lysozyme activity and total immunoglobulin (Ig) levels in plasma, liver, kidney, and skin mucus ( p < 0.05). Antioxidant markers such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and reduced glutathione (GSH) were significantly elevated in hepatic and intestinal tissues of FSOC‐fed fish, accompanied by a significant reduction in malondialdehyde (MDA) levels ( p < 0.05), indicating improved oxidative status. Skin mucus from FSOC‐fed tilapia exhibited significantly greater bactericidal activity against Aeromonas hydrophila and Streptococcus iniae . Gut gene expressions showed different patterns in the S‐10 and S‐20 treatments, as the S‐10 treatment showed only an upregulation in tumor necrosis factor‐a ( tnf-α ) expression, while the S‐20 treatment showed upregulations in various anti‐inflammatory, proinflammatory, antioxidant, and chaperon gene expressions. Additionally, gut microbiota analysis revealed that FSOC supplementation significantly increased the abundance of beneficial microbes ( Saccharomyces sp., Lactobacillus sp., and Bacillus sp.) while reducing the presence of opportunistic pathogens ( Aeromonas sp., Vibrio sp., and Streptococcus sp.). Overall, these findings suggest that FSOC is a promising functional feed ingredient capable of improving immune competence, oxidative resilience, and gut health in Nile tilapia without compromising growth.