Abstract
A feeding trial was conducted for 60 days to determine the effects of fish meal (FM) replacement with meat and bone meal (MBM) supplemented with garlic powder on the physiological and immunohematological status of juvenile rainbow trout (Oncorhynchus mykiss; 8.26 ± 1.10 g). Eight isonitrogenous (46% crude protein) and isoenergetic (22 mJ kg−1) diets were formulated containing increasing levels of MBM 0 (control), 25, 45, and 65% with or without garlic powder (3%). Our findings indicated that garlic supplementation increased red blood cell (RBC), hemoglobin (Hb), hematocrit (Ht), white blood cell (WBC), lysozyme, ACH50, and plasma protein, whereas decreased cholesterol, urea, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and creatinine. The increase in dietary MBM without garlic supplementation resulted in elevated levels of urea, creatinine, GOT, and GPT, and reduced lysozyme, ACH50, Hb, and WBC. At the end of the feeding trial, 24-h exposure to un-ionized ammonia at 1 mg l−1 resulted in increase in cortisol and glucose, and decrease in Hb and Ht in treatments without supply of garlic. Fish fed feeds with garlic supplementation, regardless of inclusion levels of MBM, exhibited reduced plasma cortisol and glucose levels and increased survival rates under ammonia exposure conditions. In summary, dietary garlic supplementation positively influenced the immune status of rainbow trout, in particular under ammonia stress.
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