Total Replacement Of Dietary Fish Oil Research Articles

Partial replacement of dietary fish oil by beef tallow does not impair antioxidant capacity and innate immunity of red swamp crayfish, Procambarus clarkii

Beef tallow (BT) has attracted research interests of fish oil (FO) sparing in aquafeed, but total replacement of dietary FO by BT might damage aquatic animal health as a controversial issue for years. This study aimed to investigate the effects of BT partially or completely replacing FO on the health of red swamp crayfish (Procambarus clarkii), especially antioxidant capacity and immune response. Three experimental diets containing FO, BT and a blend of FO and BT (FB, 1:1) as lipid sources, respectively, were formulated to feed crayfish for 8 weeks. The results showed crayfish exhibited no significant differences (p > 0.05) in growth and body proximate composition regardless of dietary lipids. Crayfish fed a BT diet were observed higher contents of haemolymph triglyceride and free fatty acid (FFA) compared with crayfish fed FO (p < 0.05), while FB diet tended to reverse this effect. For hepatopancreas antioxidants, crayfish in the FB group showed higher levels of catalase and glutathione and lower malondialdehyde content than those in the FO group (p < 0.05). Furthermore, BT diet feeding decreased the contents of haemolymph acid phosphatase, lysozyme and total protein compared with FO diet, but FB diet tended to improve these immunological parameters. FB inclusion reversed the BT-induced suppression of nuclear factor kappa beta mRNA expression and enhancement of mitochondrial manganese mRNA expression versus BT, implying ameliorative immunity function. Taken together, total replacement of dietary FO by BT might be detrimental to the health of crayfish, while partial substitution of dietary FO with BT neither suppresses growth nor impairs antioxidant capacity and innate immunity of crayfish.

Effects of total replacement of dietary fish oil on growth performance and fatty acid compositions of hybrid tilapia (Oreochromis niloticus × O. aureus)

The aim of this study is to evaluate the effects of total replacement of fish oil (FO) with pork lard (PL), soybean oil (SO), or tea seed oil (TO) on growth and fatty acid compositions of hybrid tilapia (Oreochromis niloticus × O. aureus). Four diets were formulated to contain 4.5 % of each of the different lipid sources. Each diet was assigned to triplicate groups of 15 hybrid tilapia with the same initial body weight (4.6 ± 0.5 g). After a 10-week feeding, the FO, SO, and TO groups had similar final body weight. The mean hepatosomatic index in the FO group was significantly lower than the other groups (2.5 vs 2.9–3.0; P < 0.05). Whole-body lipid levels were highest in the TO group (5.2 ± 0.4 %) and lowest in the FO group (4.3 ± 0.5 %). Total n-3 polyunsaturated fatty acids (PUFA) concentrations were greater in the SO and FO groups (5.5 ± 0.1 and 7.1 ± 0.2, respectively) than in the PL and TO groups (1.7 ± 0.1 and 1.4 ± 0.1, respectively). The FO group had a 2- to 4-fold reduction in the n-6/n-3 PUFA ratio relative to the other groups. The concentrations of both docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were significantly (P < 0.05) higher in the FO group than in the other groups. Our data demonstrate that total replacement of dietary FO with SO or TO has little effects on growth of hybrid tilapia but reduces the contents of health-benefiting DHA and EPA in fish body.

Effects of substitution of dietary fish oil with a blend of vegetable oils on liver and peripheral blood leucocyte fatty acid composition, plasma prostaglandin E2and immune parameters in three strains of Atlantic salmon (Salmo salar)

Duplicate groups of three genetic strains of Atlantic salmon smolts were cultured on diets containing either fish oil (FO) or a blend of vegetable oils (VO). Fatty acid compositions of liver and peripheral blood leucocytes were compared. The effect of different strains and diets on innate immune parameters and plasma prostaglandin E2 were also measured. Two strains were selected as being either ‘fat’ or ‘lean’ in terms of muscle adiposity. The third strain was a commercial stock (MH). Total replacement of dietary FO with VO resulted in reduced docosahexaenoic (DHA; 22:6n-3) and eicosapentaenoic acids (EPA; 20:5n-3) in liver, while oleic (18:1n-9), linoleic (18:2n-6) and α-linolenic (18:3n-3) acids were all increased in VO-fed fish. Fatty acid compositions of blood leucocytes showed similar changes. Evaluation of innate immune function showed that in the fat strain, circulating leucocytes were significantly lower in VO fish. The lean strain also had significantly higher serum lysozyme activity than MH fish. Reduced haematocrit was seen in VO lean fish compared with FO lean fish. This study provides evidence of strain-induced differences in liver and leucocyte fatty acid compositions and innate immunity in Atlantic salmon fed either FO- or VO-based diets.