Abstract
The effect of replacing fish oil (FO) with linseed oil (LnO) in rohu, Labeo rohita (initial weight 19.1 ± 0.1 g), diets was evaluated in a 90-day feeding trial. Five isonitrogenous (30% crude protein) and isolipidic (11% crude lipid) diets were prepared by substitution of FO (7% FO in the control) with LnO (0, 25, 50, 75, and 100%). Responses of the fish were tested in triplicate for each diet. Partial replacements up to 75% did not cause any significant change in growth performance and feed efficiency. However, total replacement of FO significantly reduced growth performance and feed utilization (P < 0.05). Survival, hepatosomatic index (HSI), and viscerosomatic index (VSI) as well as whole-body proximate composition were not significantly influenced by the dietary treatments. The ratio of alpha linolenic acid (ALA; 18:3n-3) increased in the muscle and liver with the increasing level of dietary LnO, while the percentage levels of eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) decreased. However, EPA and DHA were in considerable level (3.3 and 18.6%, respectively) in muscle even when fed diet with 100% LnO. Hematological parameters such as red blood cell (RBC), hemoglobin (Hb), and hematocrit (Hct) were not influenced by dietary treatments, averaging 2.2 × 106 U/L, 7.6 g/L, and 27.8%, respectively. On the other hand, alanine transaminase (ALT) and aspartate transaminase (AST) activity in serum were significantly elevated with the LnO inclusion levels (P < 0.05), reaching the highest levels (33.0 and 310.7 U/L, respectively) when LnO totally replaced FO. Cholesterol (CHOL), triacylglycerol (TG), high-density lipid (HDL), and low-density lipid (LDL) levels were significantly enhanced (P < 0.05) compared to the control. Cortisol (CORT) and glucose (GLU) were not significantly changed, averaging 1.5 nmol/mL and 20.8 g/dL, respectively. In the liver and serum, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) activities were significantly reduced, while malondialdehyde (MDA) level was significantly increased (P < 0.05) with the dietary LnO inclusion. Our results indicate that FO can be substituted with LnO up to 75% in practical diet formulations for rohu without any considerable negative effect, which will substantially decrease the dependency on dietary FO.
