Abstract
Hormone-induced breeding of fish has been effectively achieved with ovaprim, a salmon GnRH analog, in several teleost fish but not quite successfully in the Indian catfish. In order to analyze the rationale behind ovaprim ineffectiveness in this species, we investigated the effect of ovaprim injection on the GnRH receptors of the ovary and other extra-pituitary organs, since GnRH receptors are known to be over-expressed during spawning. RT-PCR analysis revealed that the GnRH receptor-II is present not only in the ovary, but also in the testis, liver and heart tissues of the catfish. However, the expression of the receptor declined in a time-dependent manner in response to ovaprim injection in all the above tissues. Concomitant changes were observed in the histology of the ovary, which indicated a decrease in the number of the immature ovarian follicles, thus elucidating the rationale behind partial success of ovaprim-induced spawning in the Indian catfish, as compared to other teleosts.
Highlights
The essential need to increase the supply of animal protein has prompted many countries to seek ways to augment the production of fish through the development of more effective techniques for fish culture (Rottmann et al, 1991)
The results indicated the presence of gonadotropin-releasing hormones (GnRH) receptor-II mRNA in the ovary, testis and heart, where maximum expression was observed in the ovary and minimum in the heart (Figure 1A)
There is no data till date regarding the expression and distribution of GnRH receptors in the Indian catfish, the same has been evaluated for the African variety (C. gariepinus), where only the species-specific, hypothalamic form of GnRH, catfish GnRH and the conserved mesencephalic cGnRH-II form have been identified by peptide chemistry (Bogerd et al, 1992)
Summary
The essential need to increase the supply of animal protein has prompted many countries to seek ways to augment the production of fish through the development of more effective techniques for fish culture (Rottmann et al, 1991). The high demand for fish fingerlings in the aquaculture industry has stimulated the need for artificial propagation of cultivable warm water fish. A major factor that constrains the speed and extent of development of fish culture has been the availability of “fish seed”, viz., fry and fingerlings (Nwokoye et al, 2007). Water pollution due to rapid industrial development and the increasing use of insecticides may, in not too distant future, deplete natural spawning stocks and cause heavy mortality of larvae and fry (Dupree and Huner, 1984; Piper, 1989)
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