Endocrine sex differentiation in fish by T. J. Pandian

By T. J. Pandian

Fish represent an enormous normal renewable source and any aid of their skill to propagate because of human interference could have major socioeconomic effects. The adverse influence of human job on intercourse differentiation and reproductive output in fish is so various that it's been tricky to surround it in one ebook. This booklet serves because the first try and do so.

Unlike in mammals, the expression of a number of intercourse differentiation genes in fish is usually managed by way of environmental components. no longer strangely, environmental intercourse differentiation is ubiquitous in fish. Overexploitation through seize fisheries doesn't disrupt intercourse differentiation yet crowding in aqua-farms does, through lowering accessibility to nutrients supply.

Some of the man-made chemical compounds typically used around the globe mimic endogenous hormones. for instance endosulfan, that is regular in constructing nations, disrupts endogenous hormones and feminizes fish. For the 1st time, this booklet perspectives endocrine disruption from the purpose of labile youth and non-labile grownup phases. It exhibits that intercourse can irreversibly be reversed, whilst uncovered to endocrine disrupting chemical substances (EDCs) in the course of early labile phases yet reversibly impairs reproductive output on publicity to EDCs in the course of non-labile grownup degree. A final result of weather switch, increased temperature, and declining oxygen and pH degrees is that it masculinises genetic lady fish.

Fish exhibit a extraordinary skill to put off the labile interval. along with postponement, a few basic and tertiary gonochores have designated labile sessions amenable to temperature and hormonal manipulations. Hermaphrodites have retained the interval till the top of the grownup level and are in a position to intercourse change/reversal greater than as soon as in either female and male instructions.

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Even among the gonochores, a few individuals of Xiphophorus helleri are known to switch from female to male (Lodi, 1979). Modes of reproduction also range from sexual to gynogenesis and to hybridogenesis and each of these modes may involve external fertilization and oviparity, or internal fertilization and viviparity, which itself ranges from zygoparity to true viviparity. In fact no other vertebrate group offers as much diversity as teleost fishes for the study of sex differentiation (Pandian, 2011).

Transformation of oogonia into primary oocytes with the onset of meiosis (primary growth phase), III. Secondary growth phase characterized by significant oocyte enlargement due to the accumulation of yolk proteins (vitellogenesis) and lipids, IV. Maturation characterized by the resumption of meiosis, germinal vesicle break down, lipid and yolk coalescence and hydration, and V. Ovulation (Patino and Sullivan, 2002) (see Fig. 7). Spermatogonia and oogonia display important differences in the commencement and completion of meiotic division.

2010). A seasonal change in androgen receptor (ar) level has been reported with a five-fold peak during breeding season in Carassius auratus (Pasmanik and Callard, 1988). Larsson et al. (2002) also found a similar seasonal change in a nuclear ar during the breeding season in the brain of M. undulatus; they also confirmed that the brain ar expression is regulated by sex steroids. Spawning periodicity: The described endocrine events within a reproductive cycle are to be tuned to different periods resulting in definite patterns of reproductive periodicity in fish.

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