A Review on the Reproduction and Development in Fish
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2017, Vol 1, Issue 6
Abstract
In order that survival of young be more than optimum, the timing of spawning by the mature adult fish is so adjusted that must be closely linked to the availability of maximum congenial environment added by increased food availability of food for the newly hatched young ones. The availability of food for the larvae and juveniles of most temperate and cold water fish species varies on a seasonal basis and following this fish are usually found to have a discrete and selective spawning season so perfectly timed that hatched out larvae will get readily available exogenous food from nature for their further development. Thus, in many temperate and cold water species, spawning is an annual event. Spawning culminates a series of preparatory events during which the gametes develop and the gonads increase in size. The annual cycle of fishesgenerally categorized into three major phases: A. Post Spawning phase: Period when the gonads are thin and slender and appear to be in a resting phase. B. Pre Spawning phase: Period in which the gonads begin production of gametes (gameto genesis) and incorporation of yolk into the oocytes (vitello genesis) which is accompanied by a process known as gonadal recrudescence i.e. gradual increase in gonad size. C. Spawning phase: Period involving final maturation and ripening of the gametes; this phase culminates in spawning act, with the release of egg and milt which ensures fertilization. Thus, gonadal development is considered to encompasses a series of interrelated phases, each requiring precise coordination and control if viable gametes are to be produced at the optimum time of the year for the subsequent survival of the young fish. The production of gametes involves the manufacture and incorporation of yolk into the developing oocytes (vitello genesis). During the early part of gonadal development, the oogonia, through the process of oogenesis produce mature eggs. Primarily, under the influence of GTHI, primary oogonium forms several primary follicles which ultimately develop into mature graffian follicle. It is within this graffwian follicle eggs mature and get associated with vitallogenin protein from liver known as yolk granule, acts as a readymade food for the growing embryo during development of larvae. Supported by this endogenous food gamete grow in size during post vitallogenic phase of development alin particular. In the salmonids, for example, the oocytes increase in diameter from about 50μm to 500-1000μm prior to the start of vitellogenesis. The incorporation of yolk that occurs during the vitellogenic phase leads to the diameter of the oocyte increasing to around 5000μm (5mm). Thus, there is an enormous increase in oocyte volume during post vitellogenic phase. This observation supports the view that in majority of fishesthe gametic development is dependent on endogenous hormone and the nutrient protein from liver and its subsequent incorporation into egg cytoplasm. The yolk is derived from vitellogenin, a lipophosphorotein- calcium complex with a molecular weight of approximately 440, 000. Vitellogenin is synthesized in the liver and is then released into the blood system. The vitellogenin is then transported to the ovary through hepatic portal blood vessel from which it is sequestered by the oocyte. Following uptake into the oocyte the vitellogenin splits into two major components each having a molecular weight of 35 000, which form the yolk stores. The processes of gametic development and gonadal growth usually occur gradually and the prespawning phase of the cycle often continues for a considerable period of time, perhaps several months, before the actual spawning occurs. These indicate that the fish can ‘predict’ the arrival of spawning time several months in advance.
Authors and Affiliations
Chattopadhyay NR, Chattoraj S
Keywords
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- EP ID EP582130
- DOI 10.26717/BJSTR.2017.01.000529
- Views 153
- Downloads 0
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