Effects Of Different Dietary Oil Sources On Growth Performance,Fatty Acid Compositions And Hufa Biosynthesis Of Freshwater Fish

Fish oil(FO)has been considered as a usual source of oil in the aquafeed industry over the past years because of its high content of n-3 LC-PUFA especially EPA and DHA.So,vegetable oils are being used in the replacement of FO in aquaculture.Our purpose aimed to improve the nutritional value of fillets of freshwater fish through feeding with plant oil enriched with 18:3n-3 or 18:2n-6 as a replacer for FO.The first study devoted to detecting the effects of various sources of dietary lipid on growth performance,tissue fatty acid composition,serum parameters,and expression of some genes related to lipid metabolism in Juvenile Nile Tilapia(Oreochromis niloticus).Fish(13.15 ± 1.11g)were fed four isonitrogenous(39.5±0.4 %)and isolipidic concentration(10%)with different dietary lipid sources,which included fish oil as a control group,soybean oil(SO),camelina oil(CO)and mix of(FO,SO and CO)with equal ratios(MO)in triplicate groups(20 fish/tank).Hepatic and muscular fatty acid compositions were reflected by dietary lipids.Dietary CO led to raising the total omega 3 fatty acids(n-3)especially,alpha-linolenic acid(18:3n-3)and docosahexaenoic acid(22:6n-3)and reduce the omega 6 fatty acids(n-6)concentration in the fillets of Nile tilapia.Fish fed SO diet had the highest hepatic lipid content,whereas fish fed the FO and CO diet had the highest muscular lipid content.Serum low-density lipoprotein(LDL)concentration decreased with increasing polyunsaturated fatty acids(PUFAs)in CO and MO groups.These findings suggested that CO can be efficiently utilized by fish as FO because it increased the nutritional value of Nile tilapia fillet through the improvement of its content of highly unsaturated fatty acids.Additionally,the second study aimed to investigate the mechanism of in vivo synthesis of PUFAs and its regulation in zebrafish(Danio rerio)in response to feeding with plant oils.Zebrafish can synthesize PUFA such as EPA,ARA,and DHA through the role of Elovls and Fads.Indeed,the elovl2 gene was described in freshwater fish and functionally characterized via heterologous expression in yeast.Mammalian elovl2 is highly effective in elongation of 20-and 22-carbon PUFAs with low or no activity in the case of humans towards C18 similar to what we observed in Zebrafish.Thus,the experimental feeding of elovl2 knockout zebrafish(KO)and wild type(WT)with CO and SO diet was conducted for 4 weeks.As expected,elovl2 KO zebrafish displayed accumulated levels of 20:5n-3,22:5n-3,and 20:4n-6 as well,decreased DHA levels in liver,fillet,and gonads(ovary and testis)as compared to WT.The impaired PUFA levels positively influenced the hepatic levels of the key lipogenic transcriptional regulator sterol-regulatory element-binding protein 1c(SREBP-1c).Consequently,this study suggests that elovl2 is a crucial elongase required for 22:6n-3 synthesis in the liver,fillet,and gonads of zebrafish.