摘要：
Fatty acids,especially essential fatty acids,play an important role in the regulation of reproductive performance in marine fish.The importance of long-chain polyunsaturated fatty acids (LC-PUFA),especially 22:6n-3 (DHA),20:5n-3 (EPA)and 20:4n-6 (ARA),in broodstock nutrition has attracted attention in the last two decades.It has been well documented that dietary essential fatty acid is a nutritional factor that greatly affects spawning performance,egg and larval quality of fish.Lipids are utilized as energy sources throughout embryogenesis,and particularly in the later stages of development prior to hatching.EPA and DHA are the major fatty acids in the total lipid of eggs of most fish and these fatty acids markedly influence the reproductive parameters.DHA,especially abundant in retina and brain,has a particularly important role in maintaining the structure and function of the cell membranes of these tissues.In addition,as a major fatty acid in phosphatidylinositol and precursor of prostaglandin, ARA stimulates ovarian and testicular steroidogenesis and is assumed to be involved in embryonic development of the immune system,hatching and early larval performance.Reported studies on essential fatty acids in marine fish broodstock mainly cover four fields:(1 )Requirements.Fat provides energy and essential fatty acids for the growth of marine fishes and play critical roles in marine fish nutrition.n-3 LC-PUFA are essential fatty acids.It is typically recognized that marine fishes have a limited ability to convert shorter chain and less unsaturated fatty acids into n-3 LC-PUFA.Therefore,adequate amounts of n-3 LC-PUFA must be supplied through the diet to ensure normal growth and development.Studies on some marine fish species have shown that different fishes require different levels of n-3 LC-PUFA,and also extremely high or low levels of dietary n-3 LC-PUFA are not conducive to the normal growth and development.Hence,the provision of appropriate amounts of dietary n-3 LC-PUFA is essential.On the other hand,little attention has been given to n-6 LC-PUFA in spite of evidence in the literature suggesting its potential importance in reproduction;(2 )Reproductive performance.Dietary LC-PUFA content greatly affects egg and larval quality.In general,low LC-PUFA levels in broodstock diets decrease egg quality.However,some authors have identified negative effects of excess LC-PUFA on egg quality.To obtain LC-PUFA levels suitable for developing formulated broodstock diet,it is necessary to determine the ways in which the egg changes with the increasing levels of dietary LC-PUFA;(3 )Body fatty acids storage.Numerous earlier reports on different species of finfish have evidenced that the fatty acid compositions of tissue lipids were closely related to dietary fatty acids input.DHA was selectively deposited and retained,as ovary DHA concentrations were always higher than diet concentrations,suggesting that DHA had higher nutritional value and contributed more to the species reproduction than EPA or ARA;(4 ) Endocrine regulation.The importance of LC-PUFAs,especially n-3 LC-PUFAs,in broodstock nutrition has been extensively studied.While most studies have focused on the effects of diet on body composition,growth performance,egg quality and larval survival rate,few studies have investigated the effects of nutrients on hormone synthesis during gonadogenesis.Pituitary gonadotropin hormone (GtH),follicle-stimulating hormone (FSH)and luteinizing hormone (LH)are involved in gametogenesis and sexual maturation in teleosts.In salmonid fish, FSH is primarily involved in vitellogenesis and spermatogenesis, whereas LH triggers maturation,ovulation,and spermiation.In response to GtH,cholesterol is converted into testosterone (T) and 17β-estradiol (E2 ). E2 stimulates hepatic vitellogenin synthesis, which is essential in oocyte development.In rainbow trout,FSH levels increase during vitellogenesis and decrease during final maturation concomitant with increasing LH levels.Sex steroid hormones play important roles in vertebrate reproduction. In several teleost species,E2 and T produced in gonadal tissues under the control of GtH,are essential in gametogenesis.Fatty acids (especially PUFAs ) are cell signaling molecules,structural compounds and energy sources.PUFAs are crucial for mediating immunological,metabolic,and endocrine signals within the uterine-fetal-placental unit.PUFAs are precursors of cell signaling molecules,and there is evidence that they regulate membrane signal transduction pathways and steroid hormone action,by modulating the binding of estrogen,progesterone, and glucocorticoids to their intracellular receptors. Therefore, PUFAs act as endogenous modulators of key enzymes involved in steroid metabolism.Previous studies on fish reproduction have focused on lipids as energy sources,but their roles in other physiological processes have been overlooked in spite of the fact that PUFAs and their metabolites produced from cyclooxygenase and lipoxygenase have modulatory effects on steroid metabolism,which in turn control ovulation,steroidogenesis and fecundity rates. This paper reviewed the research on essential fatty acids in marine fish broodstock in the above four fields, especially made a comprehensive analysis on endocrine regulation of essential fatty acids,and proposed suggestions for further research on essential fatty acids in marine fish broodstock.%脂肪酸营养特别是其中的必需脂肪酸在海水鱼类生殖调控方面具有重要的生理作用.饲料中二十碳五烯酸(EPA)、二十二碳六烯酸(DHA)以及花生四烯酸(ARA)含量在调控海水鱼类性腺发育、排卵、孵化率及仔鱼质量等方面作用显著.本文主要从必需脂肪酸需求量、对繁殖性能影响、对机体脂肪酸存储影响及对内分泌调控作用4个方面归纳总结了海水鱼类亲体脂肪酸营养的研究概况,并重点分析探讨了在内分泌调控方面的研究进展,同时对后续的研究重点提出了一些建议.
