Nile tilapia, Oreochromis niloticus, (2.00 ± 0.02 g) were reared in 16 70‐L tanks (40 individual/tank) and fed diets (approx. 345 g/kg protein, approx. 87 g/kg crude fat) containing 0 (CTL), 75 (PH‐75), 150 (PH‐150), and 300 (PH‐300) mg/kg phytol (n = 4). After 60 days of feeding (4% daily), growth performance, humoral immune parameters, and gut bacteria were analyzed. Also, hepatic antioxidant parameters were determined before and after the fish were transported in plastic bags for 6 hr. The results showed that PH‐75 exhibited the highest final weight (P < 0.001), weight gain (P < 0.001), feed intake (P < 0.001), feed efficiency (P = 0.015), plasma lysozyme activity (P = 0.004), and intestinal Lactobacillus sp. population (P = 0.017), among the treatments. The highest plasma alternative complement activity (P = 0.006) and the lowest intestinal total viable bacteria (P = 0.027) were observed in PH‐75 and PH‐150. The highest plasma alkaline phosphatase activities were observed in PH‐75 and PH‐300 (P = 0.014). The highest blood leukocyte (P = 0.008), monocyte (P = 0.010), and eosinophil (P < 0.001) were observed in PH‐300, while the highest blood neutrophil was observed in all phytol treatments (P < 0.001). The highest hepatic lipid peroxidation was observed in PH‐300, whereas PH‐75 and PH‐150 showed the lowest values (P < 0.001). The highest hepatic reduced glutathione was observed in PH‐75, also PH‐150 exhibited significant elevation in this parameter, compared to CTL (P < 0.001). Transportation led to significant elevations in the hepatic antioxidant enzymes’ activities in CTL, PH‐75, and PH‐150; the highest activities were related to PH‐75 and PH‐150 treatments, which had also the highest post‐transportation survivals (P < 0.001). In conclusion, phytol is a suitable feed supplement for Nile tilapia, improving growth performance and welfare, particularly at 75 mg/kg.

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.