Fish Oil Finishing Diet Maintains Optimal n-3 Long-Chain Fatty Acid Content in European Whitefish (Coregonus lavaretus)

Feasibility of replacing fish oil with sunflower oil on the growth, body composition, fatty acid profile, antioxidant activity, stress response, and blood biomarkers of Labeo rohita

A 90-day study was conducted to investigate the effects of substituting sunflower oil (SFO) for fish oil (FO) on various parameters in Labeo rohita (initial weight 18.21 ± 0.22 g). Five experimental diets with different levels of SFO (up to 7%) substitution for FO (0%, 25%, 50%, 75%, and 100%) were formulated, ensuring equal levels of nitrogen and lipids. The results indicated that even with 100% substitution of SFO with FO, there were no significant differences (P>0.05) were observed in growth performance. The survival rate (SR), hepato-somatic index (HSI), and viscero-somatic index (VSI) as well as whole-body composition were also nonsignificant by SFO substitution. However, the fatty acid profiles in both muscle and liver were influenced (P<0.05) by dietary substitution. Saturated fats (SFA) decreased, while monounsaturated fats (MUFA), and linoleic acid (LA) increased (P<0.05). On the other hand, the contribution of linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) decreased (P<0.05) as the amount of SFO in the diet increased. Hematology parameters, including red blood cells (RBCs), hemoglobin (Hb), and hematocrit (Hct), were not affected. Globulin (GLO) levels decreased significantly (P<0.05), while alanine transaminase (ALT) and aspartate transaminase (AST) activity showed nonsignificant increases (P>0.05). Total protein (TP) increased (P<0.05) at 100% SFO inclusion in the diet, and albumin (ALB) levels increased (P<0.05) at 75% and 100% SFO inclusion in the diet. Cholesterol (CHOL), triacylglycerol (TG), and high-density lipids (HDL) were not significantly affected (P>0.05), while low-density lipids (LDL) were significantly increased (P<0.05) compared to the control group. Cortisol (CORT) and glucose (GLU) levels showed nonsignificant (P>0.05) changes. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities in the liver and serum were not significantly (P>0.05) affected, while malondialdehyde (MDA) status was significantly (P<0.05) reduced. In conclusion, the fatty acid profile of the muscle and liver of fish was modified by the diets, and FO can be substituted with SFO up to 100% for L. rohita, which is beneficial for growth and immunity while marinating the lipid contents in fish. Our study revealed that fully replacing fish oil with SFO shows promise in fully replacing FO without compromising the growth and overall health status of the fish.

Depuration of geosmin- and 2-methylisoborneol-induced off-flavors in recirculating aquaculture system (RAS) farmed European whitefish Coregonus lavaretus

European whitefish Coregonus lavaretus has increasingly become an important species for aquatic food production, especially in the Nordic countries. Whitefish is produced in traditional cage and pond operations, and in recirculating aquaculture system (RAS) in which, unfortunately, off-flavors and odors, mostly caused by geosmin (GSM) and 2-methylisoborneol (MIB), can accumulate in fish flesh from the circulating water. GSM and MIB have very low human sensory detection limits and, therefore, often disliked by consumers even at low concentrations. In this study, concentrations of GSM and MIB in RAS farmed European whitefish were studied by an analytical method based on headspace solid phase microextraction and gas chromatography–mass spectrometry. Concentrations were determined in different parts of fish: fillet, neck, belly, and tail during a depuration period and in depuration water. The highest initial concentrations were on average 32 ng g⁻¹ (GSM) and 24 ng g⁻¹ (MIB) in European whitefish fillet and 128 ng L⁻¹ (GSM) and 94 ng L⁻¹ (MIB) in water, respectively. After a depuration period of 16 days, concentrations decreased to below the detection limits, indicating the importance of the depuration period.