Abstract
A growth experiment was conducted to evaluate the effects of dietary fish oil (FO) replaced by linseed oil (LO) on the growth performance, antioxidant capacity, hepatic lipid metabolism, and expression of inflammatory genes in large yellow croaker (Larimichthys crocea). Fish (initial weight: 15.88 ± 0.14 g) were fed four experimental diets with 0% (the control), 33.3%, 66.7%, and 100% of FO replaced by LO. Each diet was randomly attributed to triplicate seawater floating cages (1.0 × 1.0 × 2.0 m) with 60 fish in each cage. Results showed that the growth performance of fish fed the diet with 100% LO was markedly decreased compared with the control group (P < 0.05), while no remarkable difference was observed in the growth performance of fish fed diets within 66.7% LO (P > 0.05). The percentage of 18:3n-3 was the highest in the liver and muscle of fish fed the diet with 100% LO among the four treatments. When dietary FO was entirely replaced by LO, fish had a markedly higher total cholesterol, total triglyceride, low-density lipoprotein cholesterol content, and alanine transaminase activity in the serum than the control group (P < 0.05). The concentration of malondialdehyde was markedly higher, while the activity of catalase was markedly lower in fish fed the diet with 100% LO than the control group (P < 0.05). When dietary FO was entirely replaced by LO, hepatic lipid content, transcriptional levels of fatp1 and cd36, and CD36 protein expression were significantly higher, while transcriptional level of cpt-1 and CPT-1 protein expression were significantly lower than the control group (P < 0.05). As for the gene expression of cytokines, fish fed the diet with 100% LO had markedly higher transcriptional levels of il-1β, tnfα, and il-6 than the control group (P < 0.05). In conclusion, the substitution of 66.7% FO with LO had no significant effects on the growth performance of fish, while 100% LO decreased the growth performance and increased the inflammation and hepatic lipid content of fish. The increase of hepatic lipid content was probably due to the increased fatty acid uptake and decreased fatty acid oxidation in fish.
Highlights
Linseed oil (LO) is rich in α-linoleic acid (18:3n-3), which is a vital fatty acid (FA) for fish to maintain good growth performance and health status (Menoyo et al, 2007; Wu and Chen, 2012)
When dietary fish oil (FO) was entirely replaced by LO, fish had markedly higher hepatic lipid content than the control group (P < 0.05)
When dietary FO was entirely replaced by LO, L. crocea had the higher activity of alanine transaminase (ALT) in the serum than the control group
Summary
Linseed oil (LO) is rich in α-linoleic acid (18:3n-3), which is a vital fatty acid (FA) for fish to maintain good growth performance and health status (Menoyo et al, 2007; Wu and Chen, 2012). Previous investigations have elucidated that LO can be effectively utilized by certain freshwater fishes; dietary FO could be partially replaced by LO in silver barb (Puntius gonionotus) (Nayak et al, 2017) or even entirely replaced by LO in murray cod (Maccullochella peelii peelii) (Turchini et al, 2011), rainbow trout (Oncorhynchus mykiss) (Filiz et al, 2017), and tilapia (Oreochromis niloticus) (Peng et al, 2016) without severely compromising the growth performance and health status. Lipid metabolism consists of lipid uptake, FA oxidation, lipid synthesis, and triglyceride-rich lipoprotein secretion (Musso et al, 2009). Lipid metabolism is a useful approach to evaluate the utilization of vegetable oils in fish (Yan et al, 2015)
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