Effects Of Phospholipid On Growth,gonad Development And Nutritional Quality Of Sea Urchin (Strongylocentrotus Intermedius)

Strongylocentrotus intermedius is one of the main economic species of sea urchins in China.Phospholipids are an important part of cell membranes and contribute to their flexibility and fluidity.Phospholipids can be used as a source of energy for embryo and early larval development.The amphiphilic properties of phospholipid structure enable it to emulsify fat and promote the digestion and absorption of lipids.Phospholipid can also fight oxidation,stress and enhance body immunity.Lecithin is an excellent source of phosphatidylcholine(PC),saturated fatty acids(SFA),unsaturated fatty acids(PUFA)and highly unsaturated fatty acids(HUFA).Thus,the main objective of the present study was to evaluate the effects of phospholipids on the growth and gonadal development of S.intermedius.The main results and conclusions were summarized as follows:(1)Effects of soya lecithin addition on the growth,antioxidant capacity,gonad development and nutritional quality of adult sea urchin(Strongylocentrotus intermedius)This study was conducted to investigate the effects of soya lecithin(SL)addition on the growth,antioxidant capacity,gonad development and nutritional quality of adult sea urchin(Strongylocentrotus intermedius).Five palm oil(PO)-based feeds were formulated with graded addition of SL(0%,1.5%,3%,4.5%,and 6%).Fish oil(FO)-based feed(6% fish oil + 0% SL)and fresh kelp(Saccharina japonica)were used as the control diets.Each diet was randomly assigned to ten cages of sea urchins(Initial weight 21.61±0.23 g).The feeding experiment was performed in autumn season and lasting for 30 days.The results showed that the weight gain rate and gonadosomatic index were decreased due to moderate or higher addition level(3-6%)of SL.A low dosage(1.5%)of SL resulted in the most ideal attractive color and antioxidant capacity.The promoting effects of SL on the gonad development were observed at a low dosage,and were reflected by more sperm,larger oocytes and a thicker oocyte layer.However,the promoting effects of SL on gonad development were eliminated as the addition level increased to 4.5%.Male S.intermedius fed 1.5% SL showed comparable gametogenesis(stage Ⅲ)to that of males fed FO and kelp.However,female S.intermedius fed formulated feeds showed markedly slower gonad development than those fed kelp,with all individuals staying in stage I and Ⅱ.The deposition of arachidonic acid(ARA,20:4n-6)increased while eicosapentaenoic acid(EPA,20:5n-3),docosahexaenoic acid(DHA,22:6n-3)and n-3/n-6 polyunsaturated fatty acid(PUFA)decreased as the SL addition increased.Although FO resulted in the highest growth rate and LC-PUFA deposition,it negatively affected the antioxidant capacity.In conclusion,the optimal SL requirement was recommended to be no more than 1.5% in the PO-based diets for adult S.intermedius from the perspective of growth,antioxidant capacity,gonad development and nutritional quality.PO based diets showed comparable effects to FO based diets on the growth performance and gonad development.These results can contribute to optimization of the feed formulation for producing S.intermedius gonads that are high in quantity and quality.(2)Effects of soybean lecithin on the growth,gonadal development,fatty acid composition of gonad and digestive tract,fatty acid synthesis and inflammation related gene expression of male sea urchin(Strongylocentrotus intermedius)This experiment was conducted to investigate the effects of dietary soy lecithin(SL)on growth,gonadal development,fatty acid composition,fatty acid synthesis and inflammation-related gene expression of adult male sea urchin.Six diets were prepared by gradient addition of soybean lecithin(SL)into palm oil-based diets,and the supplemental levels of SL in diets were 0%,0.8%,1.6%,2.4% and 3.2%,4%,respectively.Each diet was randomly fed to 8 sea urchins(Initial weight 21.82±0.14 g)for 28 days.The results showed that the weight gain rate(WGR)of 4% SL was significantly lower than that of 0% SL,and the gonadal index(GSI)of 1.6% SL was significantly higher than that of other groups.SL can promote gonad development,which is manifested as increased sperm and thickened spermatocyte layer.The gonad development of male sea urchins in 1.6% SL group is the fastest(stage Ⅲ),while that in0.8% SL group is the slowest(stage Ⅱ).With the increase of SL supplemental level,the contents of arachidonic acid(ARA,20:4n-6),eicosapentaenoic acid(EPA,20:5N-3)and N-3 / N-6polyunsaturated fatty acid(PUFA)in sea urchin gonads first increased and then decreased,while the contents of docosahexaenoic acid(DHA,22:6N-3)increased.EPA and DHA in digestive tract increased with the increase of SL supplemental level,ARA increased first and then decreased,but were significantly lower than the initial level.With the increase of SL supplemental level,the expression levels of Elovl4,Elovl5,Δ 5 and Δ 6 in gonads and digestive tracts increased first and then decreased,and reached the maximum value in 1.6%SL group.The Elovl4 gene expression level in 1.6%SL group was significantly higher than that in other groups.The expression levels of COX-2,AIF-1 and TNF-α were not significantly increased.And the transcription reached the peak in the 4% SL group.Except for the similar expression of AIF-1 in the male digestive tract,the expression of AIF-1 in the 4% SL group was significantly higher than that in other groups.In conclusion,low dose(1.6%)SL can significantly improve gonadal development and accumulation of EPA and ARA in male gonadal urchins,which may be achieved by promoting digestive tract transport to gonadal and enhancing gene expression related to fatty acid synthesis.High dose of SL induced inflammation,which may be an important factor leading to decreased growth rate and gonad retardation of male sea urchins.(3)Effects of soybean lecithin on the growth,gonadal development,fatty acid composition of gonad and digestive tract,fatty acid synthesis and inflammation related gene expression of female sea urchin(Strongylocentrotus intermedius)This experiment was conducted to investigate the effects of dietary soy lecithin(SL)on growth,gonadal development,fatty acid composition,fatty acid synthesis and inflammation-related gene expression of adult female sea urchin.Six isonitrogenous and isolipid diets were prepared by gradient addition of soybean lecithin(SL)into palm oil-based diets,and the supplemental levels of SL were 0%,0.8%,1.6%,2.4% and 3.2%,4%,respectively.Each diet was randomly fed to 8 sea urchins(Initial weight 22.00±0.12 g).The experiment lasted for 28 days.The results showed that the weight gain rate(WGR)of female sea urchins increased firstly and then decreased with the increase of SL supplemental level,and the gonad index(GSI)of female sea urchins with 1.6% SL supplemental level was significantly higher than that of other groups.The gonad development of all SL groups was similar,and all entered stage Ⅱ.The oocyte layer of 0% and 1.6% SL groups was dense and thicker than that of other groups,especially 1.6%SL.The oocyte layer of sea urchin supplemented with 3.2% SL was the thinnest compared with other groups.With the increase of SL supplemental level,female gonadal saturated fatty acid(SFA)increased first and then decreased,while monounsaturated fatty acid(MUFA)decreased.SFA of sea urchin gonads in 0% SL supplemental level group was significantly lower than that in other groups.The MUFA of 4% SL was significantly lower than that of other groups.The content of eicosapentaenoic acid(EPA,20:5n-3)in the gonads of sea urchin in 1.6%SL was significantly higher than that in other groups,the content of docosahexaenoic acid(DHA,22:6n-3)in the gonads of sea urchin in 4%SL was significantly increased,and the content of arachidonic acid(ARA,20:4n-6)in the gonads of sea urchin in 1.6%SL was significantly increased.The SFA and MUFA of female digestive tract decreased with the increase of SL supplemental level.The SFA and MUFA of female digestive tract in 0%SL supplemental level were significantly higher than those in other groups.ARA content in digestive tract of sea urchin supplemented with 1.6%SL was significantly higher than that of other groups.In female gonads and digestive tract,the transcription of Elovl4,Elovl5,Δ 5 and Δ 6 firstly increased and then decreased with the increase of SL supplemental level,and reached the peak at SL1.6.Except for the close transcription of Elovl4 and Δ 6 in female gonads,The expression of genes related to fatty acid synthesis in 1.6%SL was significantly higher than that in other groups.The transcription of COX-2,AIF-1 and TNF-α showed an increasing trend.Except for ai F-1transcription in the three SL supplemental levels in female digestive tract,the expressions of inflammation-related genes in sea urchins with 4%SL supplemental level were significantly higher than those in other groups.In conclusion,a lower dose of SL(1.6%)can significantly improve gonadal development and accumulation of EPA and ARA in female gonadal urchins,which may be achieved by promoting digestive tract transport to gonadal and enhancing gene expression related to fatty acid synthesis.High dose SL induced inflammation,which may be an important factor leading to decreased growth rate and gonad retardation of female sea urchins.Summary of research conclusions: The optimal SL supplemental level for gallbladder formation of middle sea urchin is no more than 1.5%,and the diets with PO as the main fat source and FO as the main fat source have similar effects on growth performance and gonad development.Lower dose of SL(1.6%)significantly increased gonadal development in both male and female,and increased accumulation of EPA and ARA in gonadal,possibly by promoting digestive tract transport to gonadal and enhancing gene expression related to fatty acid synthesis.High dose of SL induced inflammation,which may be an important factor leading to decreased growth rate and gonad retardation in both male and female sea urchins.Because no research is pointed out that the demand of phospholipids of sea urchins(Strongylocentrotus intermedius),so need to determine its demand of phospholipids,In this process,it was found that low dose of phospholipid could improve the growth and development of sea urchins,while high dose of phospholipid could inhibit the growth and development of sea urchins.Therefore,follow-up experiments were designed to explore the reasons and to distinguish between genders in order to exclude possible interference caused by different genders.