Problems and prospects of hormone, chromosome and gene manipulations in fish

Hormonal induction of sex reversal is possible in 50 species. Dietary administration may be avoided by adopting immersion technique. Neuropeptide Y, aromatase inhibitor and temperature are now used to induce sex reversal. Embryonic events namely, insemination, second polar body extrusion and suppression of the first mitotic cleavage are manipulable to render 37 different types of ploidy induction possible. In combination with cryopreservation, androgenesis restores species. Unconventional pathways of gametogenesis in fertile triploids are described. Any method that increases heterozygosity enhances viability of tetraploids. More than 40 fish growth hormone cDNA and genomic sequences are isolated, characterized and used for construction of 'all-fish' gene cassettes for transformation. Non-invasive methods of sample collection by drawing blood and clipping fins are newly used to confirm the stable integration. Mosaic integration is an ubiquitous feature of transgenic fish. An integrated transgene may be excluded during successive cell cycles.