Alleviation of Crowding Stress in Rainbow Trout (Oncorhynchus mykiss) Through Dietary Sinapis alba Oil: A Focus on Immune and Antioxidant Responses

Aim to study:Intensive aquaculture practices, particularly high stocking density, induce chronic stress in fish andimpair growth, immunity, and health. This study aimed to evaluate the effects of dietary white mustard(Sinapis alba)oil (WMO) on crowding stress in rainbow trout(Oncorhynchus mykiss).Materials and methods:A total of 360 fish (45.2 ± 1.5 g) were distributed into six tanks and fed one of threeisonitrogenous and isocaloric diets for 60 days: control, 2.5% WMO, or 5% WMO. After the feeding trial, fish wereexposed to crowding stress at 60 kg/m³ for 14 days. Growth performance, hematological parameters, antioxidantenzymes, immune responses, and plasma cortisol and glucose levels were evaluated.Results:Dietary WMO supplementation, especially at 5%, significantly improved final weight, weight gain, andspecific growth rate compared with the control group. After crowding stress, the WMO5 group showed significantlyreduced plasma cortisol and glucose levels. WMO supplementation also enhanced antioxidant status by increasingSOD, CAT, and GPx activities and reducing MDA levels. In addition, lysozyme activity, respiratory burst activity,and total immunoglobulin levels were significantly improved in WMO-fed fish.Conclusion:Dietary supplementation with 5% white mustard oil may be an effective nutritional strategy to improvegrowth, reduce oxidative stress, enhance immune responses, and increase the resilience of rainbow trout to crowdingstress under intensive aquaculture conditions.