Hormones, pheromones and reproductive behavior

Fish commonly use reproductive hormones (steroids and prostaglandins) both as endogenous signals between reproductive tract and brain and as exogenous signals (hormonal pheromones) that synchronize gamete maturation and/or spawning interactions between and among conspecifics. This dual function for hormonal products not only extends traditional concepts that sex hormone actions are limited to reproductive synchrony within the individual, but also implies we are unlikely to achieve a comprehensive understanding of reproductive function in any fish without knowledge of both the endogenous and exogenous actions of its hormones and related released compounds. Such knowledge is beginning to accumulate for several species (e.g. goldfish, Atlantic salmon), but even here is far from complete. Moreover, because hormonal pheromone studies have focused on oviparous gonochorists with relatively simple reproductive strategies, we know nothing about the potential hormonal pheromone functions of the numerous species with sequential hermaphroditism or alternative male strategies, or the possible changes in pheromone function associated with the numerous transitions from oviparity to viviparity. Given the insights we have gained from studies of traditional species, it seems certain that expanding hormonal pheromone research to non-traditional species exemplifying the diverse nature of fish mating systems will similarly enrich our understanding of fish reproductive function.     

Ecoepidemiology of the effects of pollution on reproduction and survival of early life stages in teleosts

Evidence from the field and laboratory has shown that reproduction and early life-stage survival of several species of teleost fishes have been adversely affected following the release of several classes of synthetic, organic chemicals into the environment. Field studies from many geographic areas over several decades have found associations between exposure to synthetic chemicals in the environment and effects on hatchability, embryological success and larval survival. In more recent research, exposure to sewage treatment and bleached kraft mill effluents has been correlated with changes in reproductive system development and alterations in the endocrine physiology of wild teleost fishes. Loss of fecundity and damage during various stages of development and reproduction have been associated with exposure to endocrine disruptors, including many currently used chemicals. The supporting laboratory studies have confirmed that various wild fish species are sensitive to certain synthetic chemicals at levels of exposure of parts per billion and parts per trillion, concentrations that are biochemically, physiologically, and environmentally relevant. This paper reviews the relevant field and laboratory research, and organizes the studies using the ecoepidemiological criteria of time-order, strength of association, specificity, consistency on replication, coherence and predictive performance. There is sufficient evidence to conclude that ambient concentrations of synthetic chemicals in some regions are at or above concentrations at which certain species could be affected. The viability of fishery resources must be linked not only to the quantity of habitat but also to the quality of habitat.     

Identification of essential habitats: Including chimaeras into current shark protected areas

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鲟鱼生殖内分泌学研究进展

目前所有鲟形目鱼类均处于不同程度濒危状态,物种保育形势非常紧迫。鲟鱼生殖内分泌生理学研究是研究鲟鱼类生殖特性和人工繁殖的理论基础,对于物种保护和水产养殖均具有重要价值。与硬骨鱼类比较,目前人们对鲟鱼生殖内分泌的研究相对较少,研究集中在下丘脑-脑垂体-性腺轴所调控的生殖生理特性,已经对生殖轴上关键内分泌激素(如促性腺激素释放激素、促性腺激素类和性类固醇激素等)和环境因素对鲟鱼生殖内分泌的影响开展初步研究,生殖内分泌学研究手段已经成为评估野生和养殖鲟鱼类的生殖发育状况的重要工具。对鲟鱼生殖内分泌学研究进展进行简要概述,为进一步深入研究鲟鱼的生殖特性提供有益的参考资料。     

Hormones and Egg/Larval Quality in Fish

Recent evidence suggests that hormones are passed on to eggs by broodfish. This store of maternal hormones may fill the regulatory needs of fish larvae for growth, development, osmoregulation, stress response and other physiological functions prior to the functional development of their own endocrine glands. Thus the hormonal levels in eggs/larvae may be an important determinant of egg/larval quality.
Thyroid hormones have been best studied in this regard. Both thyroxine (T₄) and triiodothyronine (T₃) are present in fish eggs and in most cases, the levels decrease as development proceeds until the onset of endogenous thyroid hormone production, which usually occurs before or at around yolk-sac resorption. Enhancement of T₄/T₃ levels in newly-hatched larvae through immersion or maternal injection has been shown to promote larval growth, development and/or survival in several fish species, although overdose causes thyrotoxicosis.
Other hormones such as corticosteroids, sex steroids, growth hormone and prolactin are also being studied, but to a much lesser extent.
The paper reviews the evidence and discusses the practical implications of the various findings for larval rearing in aquaculture.     

Pesticide—induced reproductive dysfunction in Indian fishes

Numerous studies are available reporting the effects of pesticides on reproductive activity in Indian fishes. The majority of these reports deals with histopathological changes in gonads and endocrine glands involved in the regulation of reproduction following treatment with different pesticides. Pesticides are reported to cause degenerative changes in gonads and arrest gametogenic processes either by acting directly on the gonads or by interfering with the secretory activity of the hypothalamo-hypophyseal-gonadal/thyroid axis that regulates various reproductive events. Secretion of hormones such as gonadotropin-releasing hormone (GnRH), gonadotropin, growth hormone, adrenocorticotropic hormone (ACTH), testosterone, estrogens, 17,20β-dihydroxyprogesterone and thyroid hormones are in general lowered, leading to cessation of gametogenesis, vitellogenesis, oocyte maturation, ovulation, spermiation, etc. Adverse effects of pesticides have also been demonstrated on fecundity, fertilization, hatching, and postembryonic development. The effects are highly variable and depend on the nature, dose, and mode of application of the pesticides.     

Role of photoperiod and melatonin in the regulation of ovarian functions in Indian carp <Emphasis Type="Italic">Catla catla</Emphasis>: basic information for future application

The major carp Catla catla is a popular freshwater edible fish and an extensively cultured species in India. However, basic information on the physiology of reproduction is lacking in this species. By virtue of its surface feeding habit, it maintains close contact with environmental light, and is a species of choice for the study of temporal organization of reproduction under natural and experimental conditions for understanding environmental and/or endocrine mechanisms that control the annual reproductive cycle. The present review covers information gathered in recent years to emphasize the temporal pattern of reproductive events and the importance of photoperiod and melatonin, a hormone of the pineal gland that links the environment with the endocrine system in the regulation of reproduction. Finally, the outcome of the research is discussed in terms of its direct and indirect applications to aquaculture of this species with a view to manipulate its breeding at a desired time of the year to meet market demand.     

泛甲壳动物激素调控卵黄蛋白原合成的分子机制研究进展

昆虫和甲壳动物由于进化上亲缘关系近统称泛甲壳动物，大多数泛甲壳动物卵黄蛋白原为雌性特异性蛋白，是卵母细胞中储存的卵黄蛋白的前体，可为胚胎发育提供营养和能量，是决定繁殖性能的关键因素，在生殖发育起着十分重要作用。业已证明，调控泛甲壳动物卵黄蛋白原的主要激素有保幼激素、蜕皮激素、神经肽和胰岛素样肽等。昆虫保幼激素和蜕皮激素发挥促进作用，而神经肽和胰岛素样肽对卵黄蛋白原合成的调控作用因种类不同存在不同。除了以上激素，甲壳动物特有的眼柄高血糖激素家族以及促雄腺激素对卵黄蛋白原的合成起负调控作用。本文总结了近年来泛甲壳动物卵黄蛋白原合成的调控机制的相关研究，概括并比较了调控昆虫与甲壳动物的卵黄蛋白原合成的主要激素及调控机制，为养殖虾蟹甲壳动物生殖调控相关研究提供参考。     

三苯基锡对褐菖鮋卵巢发育的影响

尽管三苯基锡(triphenyltin,TPT)与三丁基锡(tributyltin,TBT)在海洋环境中经常同时存在,但相对于TBT,对TPT的毒性研究还较少。本实验以海洋经济鱼类褐菖鲉(Sebastiscus marmoratus)为对象,研究环境水平TPT对卵巢发育的影响。结果发现,TPT抑制了卵巢发育,表现为性腺指数的降低。TPT还诱导卵巢总脂质水平的增加,而卵巢脂质蓄积可能影响卵巢的正常生殖功能。另外,TPT暴露后,卵巢游离睾酮水平增加,卵巢游离17β-雌二醇水平降低;同时,血清三碘甲腺原氨酸水平降低。因此,TPT对性激素和甲状腺激素水平的影响可能是其抑制卵巢发育的重要机制。实验结果为全面了解TPT产生鱼类生殖毒性效应、途径和机制提供了新的重要的资料。     

卵黄蛋白原研究及其进展

甲壳动物和昆虫由于进化上亲缘关系近,被统称泛甲壳动物,大多数泛甲壳动物卵黄蛋白原为雌性特异性蛋白,是卵母细胞中储存的卵黄蛋白的前体,可为胚胎发育提供营养和能量,是决定繁殖性能的关键因素,在生殖发育中起着十分重要的作用。已有研究证明,调控泛甲壳动物卵黄蛋白原的主要激素有保幼激素、蜕皮激素、神经肽和胰岛素样肽等。昆虫保幼激素和蜕皮激素发挥促进作用,而神经肽和胰岛素样肽对卵黄蛋白原合成的调控作用因种类不同而存在不同。除了以上激素,甲壳动物特有的眼柄高血糖激素家族以及促雄腺激素(IAG)对卵黄蛋白原的合成起负调控作用。本文总结了近年来泛甲壳动物卵黄蛋白原合成调控机制的相关研究,概括并比较了调控昆虫与甲壳动物的卵黄蛋白原合成的主要激素及调控机制,为养殖虾蟹甲壳动物生殖调控相关研究提供参考。

     

Glycoprotein hormone in the pituitary of hagfish and its evolutionary implications

The pituitary gland is present in all vertebrates, from agnathans (jawless vertebrates) to mammals, but not in invertebrates. Reproduction in gnathostomes (jawed vertebrates) is controlled by two pituitary gonadotropins (GTHs), luteinizing hormone and follicle-stimulating hormone, which are part of the pituitary glycoprotein hormone (GPH) family. Hagfishes, which lack both jaws and vertebrae, are considered the most primitive vertebrate known, living or extinct. Accordingly, they are of particular importance in understanding the evolution of the pituitary GPHs and their functions related to vertebrate reproduction. Nevertheless, key elements of the reproductive endocrine system in hagfish have yet to be elucidated. Our current report has revealed the first identification of a functional GPH composed of two subunits that possess gonadotropic action at the pituitary of brown hagfish. It seems most likely that an ancestral GPH gave rise to only one GTH in hagfish pituitary and that multiplicity of GPHs arose later during the early evolution of gnathostomes. This paper briefly summarizes the latest findings on the hagfish GPH from an evolutionary point of view.     

Reproductive success and fry production of the paiche or pirarucu,Arapaima gigas (Schinz), in the region of Iquitos,Perú

Arapaima gigas (paiche) is the largest scaled fish species living in the Amazon basin. Its biology is both fascinating and misunderstood. In a context of overfishing, hence reduced natural populations, aquaculture of a fish with such interesting characteristics (large size, high growth rate, no intramuscular spines) is an important issue. The development of farming production would also reduce the fishing pressure on natural populations and allow re‐stocking programmes in certain areas. To determine what factors may influence the reproductive success in captivity, data from breeding reports for 2007–2010 were collected among fish farmers in the region of Iquitos. In parallel, we carried out physicochemical measurements in different ponds where these paiches breed, and conducted personal interviews about the general fish management conditions. The results show that reproduction occurs throughout the year but with a higher intensity during the rainy season. It also highlights farms that have performed much better than others, but no single factor except feeding level has been clearly associated with reproductive success. The environmental control of reproduction in paiche, therefore, remains partly mysterious. To deepen this study, we recommend the systematic sexing of breeders, extending reproductive behavioural studies, and examining the limnological factors involved in fry mortality.     

海水鱼类亲体必需脂肪酸营养的研究进展

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。     

Molecular evolution of neurohypophysial hormones in relation to osmoregulation: the two fish options

In vertebrates, water and osmolyte homeostasis is controlled by at least three hormonal systems: the hypothalamo-neurohypophysial system, the renin-angiotensin-aldosterone system and the atrial natriuretic factor system. The first system implies neuroendocrine reflexes involving an afferent neural limb from osmo- and baroreceptors to hypothalamus and an efferent endocrine limb from secretory neurons to target cell receptors and transduction to intracellular effectors, namely water and sodium channels. Evolution can affect any level of this molecular cascade. Whereas virtually all vertebrate species have two neurohypophysial hormones, an oxytocin-like and a vasopressin-like peptides, the most primitive vertebrates, Cyclostomata (lampreys and hagfishes) possess a single peptide, vasotocin, so that an early gene duplication occurred before the emergence of fishes, about 400 million years ago. The remarkable evolutionary stability of neurohypophysial hormones in bony vertebrates allows us to trace two main lineages: isotocin-mesotocin-oxytocin and vasotocin-vasopressin. In contrast, in cartilaginous fishes, the oxytocin-like peptides display a great evolutionary diversity: we have identified glumitocin in rays, aspargtocin and valitocin in the spiny dogfish, asvatocin and phasvatocin in the spotted dogfish, and oxytocin in the chimaera. Whereas bony vertebrates regulate their blood osmotic pressure (about 250–450 mOsm kg^-1 H₂O) essentially through salts, cartilaginous fishes use urea as the main osmolyte for adjusting their osmotic pressure above the external medium (about 1050 mOsm kg^-1 H₂O for marine fishes). The hypothesis is made that the stability of neurohypophysial hormones in bony vertebrates is due to their implication in ion-based osmoregulation (selective evolution), whereas in Chondrichthyes the occurrence of urea-based osmoregulation has relieved the hormones from this function and therefore made them free to vary (neutral evolution).     

Ascorbic acid and reproduction in fish: endocrine regulation and gamete quality

High ascorbic acid concentrations have been associated with gonad and brain tissues in teleost fishes. Although a direct dietary effect on gamete quality has been given some attention recently, the mechanism of action of ascorbate along the cascade of reproductive events in the hypothalamus, pituitary and gonads has not been defined. Data relating to gamete production and quality, as well as a possible protective role for ascorbate against cumulative genetic defects during gametogenesis and congenital malformation during gestation (embryonic development) is reviewed. It is suggested that the gonad growth in response to gonadotropin stimulation involves direct interaction between catecholamines and steroid hormones and their receptor sites. This interaction acts as a regulatory mechanism of ascorbate absorption, transfer and metabolism (degradation and/or renewal) in the reproductive system. We conclude that ascorbic acid is a leading nutrient in reproductive tissue functions and further research is needed on: (1) its antioxidant effect on gametes' (sperm and ova) capacity to prevent DNA damage occurring prior to (endogenous) and after spawning (environmental insults); (2) its dietary requirement to optimize survival and physiological recovery in multiple spawners; (3) the integration mechanism of ascorbic acid action as part of the overall endocrine regulation of neurohormonal–hormonal pathway in fish reproduction; and (4) the possible role for ascorbate in regulating fish maturation and/or infertility in the presence of enhanced UV-radiation or conditions of intensive aquaculture (hypoxia, oxygen supersaturation, dietary pro–, and antioxidants).     

Factors affecting the reproductive efficiency in crayfish: implications for aquaculture

In recent years, crayfish aquaculture industry has been developing rapidly in different regions of the world. Crayfish aquaculture is often carried out in dams, lakes and extensive pond systems. There is an increasing demand for crayfish juvenile in aquaculture sector. Therefore, it is important to know which factors affect reproductive efficiency in crayfish. In the present review, factors affecting the reproductive efficiency of crayfish are divided into two main sections, external and internal factors. Dietary lipids, phospholipids, highly unsaturated fatty acids, protein and amino acids, vitamins and carotenoids are important external factors affecting broodstock crayfish reproduction. In addition, various external (i.e. female size, stocking density, temperature, photoperiod, sex ratio) and internal (i.e. endogenous hormones) factors affect the reproductive efficiency in crayfish. This study reviews the present knowledge with the purpose of realizing the factors that are important to reach optimal crayfish nutrition, maturation and reproduction (i.e. pleopodal egg number and quality). This review will particularly be useful for crayfish farmers and crayfish hatchery units.     

α-黑素细胞刺激素及黑皮质素受体-4在能量平衡和繁殖中的功能研究

阿片黑素促皮质激素原(POMC)是黑皮质激素的前体物质,在机体中广泛分布。近年来,POMC及其衍生物黑素细胞刺激素(MSH)和黑皮质素受体-4(MC4R)在能量稳态和繁殖活动中的作用备受关注。研究发现,POMC神经元及其加工后的产物对摄食和体重的调节具有重要作用。此外,POMC神经元在下丘脑中与GnRH神经元紧密接触,由其产生的神经递质和神经肽可能对GnRH神经元具有重要的输入作用,从而直接或间接地调控下丘脑–垂体–性腺轴(HPG)中繁殖相关激素的合成并影响生殖活动。本文综述了黑皮质素系统对能量稳态和繁殖活动的调控作用以及目前MC4R在硬骨鱼类中的药理学研究,以期其能够在动物的生长发育和繁殖中具有应用前景。     

The remarkable reproductive diversity of teleost fishes

Teleosts display the most striking reproductive diversity of all vertebrates. However, no convincing hypothesis has yet been proposed to explain why they have evolved this remarkable variability in their modes of reproduction. Some of the features of the reproductive biology of teleosts are briefly reviewed, and unique characteristics of the group that may have made possible the evolution of their remarkable reproductive diversity are considered. These include whole‐genome duplication, the mode of differentiation of the gonads and the organization of the brain–pituitary relationship.     

Thyroid gland development in Senegalese sole (Solea senegalensis Kaup 1858) during early life stages: A histochemical and immunohistochemical approach

A key to success in the culture of marine fish species is the mass production of high quality fry, a process largely dependent on successful first feeding and normal development and growth of fish larvae. In this regard it is important to examine the structural and functional development of the endocrine system (pituitary, thyroid, interrenal glands) during early ontogeny of marine fish. Particularly, the thyroid hormones, thyroxine (T₄) and triiodothyronine (T₃), influence numerous metabolic processes, such as growth, differentiation, metamorphosis, reproduction, respiration, migratory behaviour, central nervous system activity, seasonal adaptation, etc. Therefore the aim of this study was to describe the development of the thyroid gland and the ontogeny appearance of the thyroid hormones in Solea senegalensis larvae by means of histological and immunohistochemical techniques. The first thyroid follicle was present at 4 days-post-hatch (dph) coinciding with first feeding. During metamorphosis (12–20 dph) the follicles increased in both number and size, and by 30 dph presented the same characteristics as that seen in adult fish. Tissue immunostaining of both thyroid hormones decreased during the endogenous larvae development to nearly undetectable levels at the completion of yolk-sac absorption. During larvae exogenous phase, T₃ and T₄ immunostaining was first detected by 6 dph and an increase of specific staining for both hormones was detected between 12 and 20 dph, during metamorphosis phase.     

Insights into Insulin and Glucagon Responses in Fish

The focus of this review is the response of insulin and glucagon to various experimental and physiological conditions in fish. Circulating levels of insulin and glucagon have been analyzed in several fish species, principally salmonids. It is generally accepted that, in fish, the insulin secretion in response to amino acids is stronger than to glucose, although this information has been obtained mainly from carnivorous species. Studies of other species demonstrate that the alimentary pattern affect hormonal secretion and should be taken into account when the effects of secretagogues are analyzed. There are few studies of glucagon secretion, even in salmonids, although it is known that amino acids also stimulate its release. The level of this response and its relationship to insulin secretion depends upon the species of fish. We will discuss the significance of these observations, while also considering other important factors, including the influence of neuropeptides and interactions with other pancreatic and gastro-intestinal hormones. Finally, seasonal, temperature and reproductive stage effects will be discussed, all of which should be taken into account when attempting to understand the role of pancreatic hormones in fish. This short review will not cover the action of these hormones on their target tissues.