Effects of garlic extract (Allium sativum) in the diet of rainbow trout (Oncorhynchus mykiss) reared in the recirculating aquaculture system: growth performance, immune response and water quality

This research was conducted to determine the effects of garlic extract as feed supplement on the growth performance, body content, blood indicators and culture water quality of rainbow trout (Oncorhynchus mykiss) under stress ammonia. A total number of 156 fish (Average weight 18.37±1.43g and total length 12.27±0.52cm) were reared in twelve 50-L tanks for 60 days (First period: 50 days of feeding with different levels of garlic extract) and (Second period: 10 days under ammonia stress of 0.024 mg /L). Experimental included adding different levels of extract to base food, 0, 0.5, 1 and 1.5% (control, A1, A2 and A3, respectively). The growth performance was significantly higher in fish fed garlic extract supplementation than control. There was a significant difference in feed conversion ratio between different treatments, so that was obtained the lowest in A2 and the highest in control. Protein, immunoglobulin and cortisol concentrations were significantly affected by different levels of garlic. The end of the experiment period, the fish were kept in a close recirculation system for 24 hours. Water sampling was carried out every 4 hours. Water ammonia increased from 16 to 24 hours of the test. At the end of the experiment (time 24), the highest ammonia was obtained in treatment A3 (0.43). In general, the results showed that the addition of 1 to 1.5% garlic extract improved the growth performance and immune response in rainbow trout, while in the recirculation system, the water quality of the rearing environment was better in the control treatment.