Spermatogenesis in fish.

Endocrine manipulations of spawning in cultured fish: from hormones to genes

Publisher Summary This chapter discusses the functional morphology of teleost gonads. Information presented in this chapter indicates that there are several processes of germ cell development, which are closely associated with changes in cellular activities of somatic cell elements. Recent studies on biochemical aspects of vitellogenesis in teleosts have shown that the hepatic and ovarian yolk proteins are similar to those of amphibian species. An in vitro method involving the separation of the follicular components has facilitated investigations of the detailed mechanism of the production of two major follicular steroid hormones. As a result of the usage of this technique, a two cell-type model involving thecal and granulosa cell layers has been proposed for the production of these two steroids for the first time in lower vertebrates. With further refinements this well characterized incubation procedure should provide an excellent system for studying the molecular basis of the mechanism of gonadotropin action on follicular steroidogenesis.

6 The Functional Morphology of Teleost Gonads

https://digital.csic.es/bitstream/10261/44722/1/Mylonas_Fostier_Zanuy-GCE.pdf

Broodstock management and hormonal manipulations of fish reproduction

Captive breeding programs are increasingly being initiated to prevent the imminent extinction of endangered species and/or populations. But how well can they conserve genetic diversity and fitness, or re-establish self-sustaining populations in the wild? A review of these complex questions and related issues in salmonid fishes reveals several insights and uncertainties. Most programs can maintain genetic diversity within populations over several generations, but available research suggests the loss of fitness in captivity can be rapid, its magnitude probably increasing with the duration in captivity. Over the long-term, there is likely tremendous variation between (i) programs in their capacity to maintain genetic diversity and fitness, and (ii) species or even intraspecific life-history types in both the severity and manner of fitness-costs accrued. Encouragingly, many new theoretical and methodological approaches now exist for current and future programs to potentially reduce these effects. Nevertheless, an unavoidable trade-off exists between conserving genetic diversity and fitness in certain instances, such as when captive-bred individuals are temporarily released into the wild. Owing to several confounding factors, there is also currently little evidence that captive-bred lines of salmonids can or cannot be reintroduced as self-sustaining populations. Most notably, the root causes of salmonid declines have not been mitigated where captive breeding programs exist. Little research has also addressed under what conditions an increase in population abundance due to captive-rearing might offset fitness reductions induced in captivity. Finally, more empirical investigation is needed to evaluate the genetic/fitness benefits and risks associated with (i) maintaining captive broodstocks as either single or multiple populations within one or more facilities, (ii) utilizing cryopreservation or surrogate broodstock technologies, and (iii) adopting other alternatives to captive-rearing such as translocations to new habitats. Management recommendations surrounding these issues are proposed, with the aim of facilitating meta-analyses and more general principles or guidelines for captive-breeding. These include the need for the following: (i) captive monitoring to involve, a priori, greater application of hypothesis testing through the use of well-designed experiments and (ii) improved documentation of procedures adopted by specific programs for reducing the loss of genetic diversity and fitness.

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How well can captive breeding programs conserve biodiversity? A review of salmonids

Changes in fertilization and hatching rates with time after ovulation induced by 17, 20β-dihydroxy-4-pregnen-3-one in the Japanese eel, Anguilla japonica

The eel has long been esteemed as an important food fish in the world, especially in Japan, and has been used as an experimental fish for many fields of fish physiology. However, the decreases in eel resources have been a serious concern in recent years. The catches of glass eels as seedlings for aquaculture have shown a long-term decrease in both Europe and East Asia. To increase eel resources, the development of techniques for artificial induction of maturation and spawning and rearing their larvae have been eagerly desired. Recent progress of reproductive physiology of fish, especially mechanisms of oocyte maturation and ovulation in female and of spermatozoa maturation in male, facilitate to establish techniques for hormonal induction of maturation and spawning in sexually immature eels. With persistent effort to development of rearing techniques of larvae, we have first succeeded to produce glass eel. These applied techniques are may contribute to understand the basic reproductive physiology of the eel.

/pdf/the-first-success-of-glass-eel-production-in-the-world-basic-217wdtxx0l.pdf

The first success of glass eel production in the world: basic biology on fish reproduction advances new applied technology in aquaculture

Diluent for cool storage of the Japanese eel (Anguilla japonica) spermatozoa

The effects of injection of 17,20ƒÀ-dihydroxy-4-pregnen-3-one (DHP) on induced ovulation in the artificially matured Japanese eel Anguilla japonica were examined, with special reference to the effect of injection time on the time of ovulation. Ovulation occurred 18 h and 21 h after injection of DHP at 9:00, in 10 of 15 females and in the remaining 5 females, respectively. Injection of DHP at 18:00 in duced ovulation 15, 18, and 21 h after injection in 4, 12, and 2 of 18 females, respectively . Fertility and hatching rates were not significantly different between females which ovulated 18 h after injection at 9:00 or 18:00. In the second experiment, eggs from females which ovulated 15 h after DHP injection showed significantly higher fertility (about 63%) and hatching rates (about 54%) than eggs from fe males which ovulated 18 h after the injection. These results indicate that the time of ovulation depends on the time elapsed after the DHP injection in the eel.

Hiromi Ohta

Papers

Changes in fertilization and hatching rates with time after ovulation induced by 17, 20β-dihydroxy-4-pregnen-3-one in the Japanese eel, Anguilla japonica

The first success of glass eel production in the world: basic biology on fish reproduction advances new applied technology in aquaculture

Diluent for cool storage of the Japanese eel (Anguilla japonica) spermatozoa

Induced Ovulation by Injection of 17, 20β-Dihydroxy-4-pregnen-3-one in the Artificially Matured Japanese Eel, with special Reference to Ovulation Time

Milt Production in the Japanese Eel Anguilla japonica Induced by Repeated Injections of Human Chorionic Gonadotropin