Document Type : Original research
Authors
Department of Fisheries, Faculty of Agriculture Sciences and Natural Resources, Azadshahr Branch, Islamic Azad University, Azadshahr, Iran
Abstract
This study investigated the effect of replacing dietary fish oil (FO) with poultry fat (PF) on some growth and blood parameters of rainbow trout (Oncorhynchus mykiss) to find a suitable alternative to fish oil. For this aim, 600 rainbow trout juveniles weighing 50.72±2.13 g were purchased and after the adaptation period, 25 fish in each pond were released in a completely randomized design with 9 treatments and 3 replications. Five diets were considered for two months containing 100%, 75%, 50%, 25%, and 0% FO (D1, D2, D3, D4, and D5, respectively), where FO was replaced with PF. The treatments were CTL (D1), 25PF (D2), 25PFR (D2, then D1), 50PF (D3), 50PFR (D3, then D1), 75PF (D4), 75PFR (D4, then D1), 100PF (D5), and 100PFR (D5, then D1). FO replacement with PF had no significant influence on growth parameters. Hepatosomatic index (HSI) increased significantly in 75PF and 100PF (P<0.05), but not in 75PFR and 100PFR (P>0.05). Some hematological, e.g. red and white blood cell counts (RBC and WBC, respectively), and serum biological parameters, e.g. glucose, triglyceride, and albumin, changed significantly (P<0.05), especially in 75PF and 100PF. The antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were downregulated in 75PF and 100PF, whereas return to D1 significantly increased the activity of these enzymes in 75PFR and 100PFR (P<0.05). Furthermore, intestinal lipase activity fell significantly in 50PF, 75PF, and 100PF (P<0.05) but not in those fed D1 on the second month (P>0.05). Intestine structure was severely damaged in all groups except 50PF, 75PF, and 100PF, which indicates the oxidative stress imposed on fish fed diets with higher FO. In summary, a balance should be maintained between FO and alternative fat in fish diet to retain the best growth efficiency and prevent from adverse effects of either fat source.
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