Abstract
The present study was conducted to explore the mechanisms leading to differences among fishes in the ability to biosynthesize long-chain polyunsaturated fatty acids (LC-PUFAs). Replacement of fish oil with vegetable oil caused varied degrees of increase in 18-carbon fatty acid content and decrease in n-3 LC-PUFA content in the muscle and liver of rainbow trout (Oncorhynchus mykiss), Japanese seabass (Lateolabrax japonicus) and large yellow croaker (Larimichthys crocea), suggesting that these fishes have differing abilities to biosynthesize LC-PUFAs. Fish oil replacement also led to significantly up-regulated expression of FADS2 and SREBP-1 but different responses of the two PPAR-α homologues in the livers of these three fishes. An in vitro experiment indicated that the basic transcription activity of the FADS2 promoter was significantly higher in rainbow trout than in Japanese seabass or large yellow croaker, which was consistent with their LC-PUFA biosynthetic abilities. In addition, SREBP-1 and PPAR-α up-regulated FADS2 promoter activity. These regulatory effects varied considerably between SREBP-1 and PPAR-α, as well as among the three fishes. Taken together, the differences in regulatory activities of the two transcription factors targeting FADS2 may be responsible for the different LC-PUFA biosynthetic abilities in these three fishes that have adapted to different ambient salinity.
Highlights
Decreasing global availability, coupled with the high cost of fish oil, has forced the aquaculture industry to investigate possible alternative sources of dietary lipids
A 70 d feeding experiment was conducted on rainbow trout, Japanese seabass and large yellow croaker to comprehensively compare the effects of different levels of vegetable oil substitution on tissue fatty acid composition and on the expression of genes related to LC-PUFA biosynthesis (FADS2, SREBP-1 and PPAR-α)
Partial or total replacement of fish oil with vegetable oil had no significant effects on Specific growth rate (SGR), Feed efficiency rate (FER), Survival rate (SR) and Feed intake (FI) compared with the control group
Summary
Decreasing global availability, coupled with the high cost of fish oil, has forced the aquaculture industry to investigate possible alternative sources of dietary lipids. Previous studies have shown that SREBP-1 is related to fatty acid metabolism[36,37] and that the gene expression of SREBP-1 and PPAR-αcan be regulated by dietary fatty acids[33] It remains unclear whether these two factors are involved in fatty acid biosynthesis by targeting FADS2. A 70 d feeding experiment was conducted on rainbow trout, Japanese seabass and large yellow croaker to comprehensively compare the effects of different levels of vegetable oil substitution on tissue fatty acid composition and on the expression of genes related to LC-PUFA biosynthesis (FADS2, SREBP-1 and PPAR-α). An in vitro experiment was conducted to investigate the activity of SREBP-1 and PPAR-αin regulating the expression of the FADS2 gene promoter
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