Biotechnology Input in Fish Breeding

Abstract

29-38Pisciculture, to increase the fish production, has a crucial limitation. Fish cultured in land-locked water bodies usually do not breed without the hormonal induction. Technology of fish breeding suffered for a long time due to the lack of suitable commercial product to induce the spawning of economically important fish. Hypophysation technique, where pituitary extract was used to induce the breeding, faced more failures than success besides the limitation of the source. After the discovery of a brain peptide, gonadotropin releasing hormone (GnRH), which binds to the membrane receptor of pituitary gonadotroph cell and releases gonadotropic hormone (GTH), the situation has changed dramatically. Final maturation and release of germ cells, spermatozoa and oocyte, to the water for fertilization, depends on an acute surge of GTH which is about 10 times greater than the normal circulatory level of GTH. Injection of GnRH causes this acute GTH surge. GnRH is a decapeptide but its gene encodes 92 amino acid containing large molecule. Extensive post-translational processing is necessary to secrete GnRH from the neural cells. For this reason recombinant DNA technology could not be employed for the production of GnRH. Instead, chemical synthesis of this decapeptide is easier and cheaper. Numbers of fish GnRH structure have been elucidated and depending on salmon GnRH peptide sequence, a chemical analogue has now been marketed under the the name of "Ovaprim". There is a strong research background to understand GnRH mechanism of action and signal transduction pathway involved in GnRH mediated GTH function on germ cell maturation and release. These scientific investigations have contributed significantly in designing the superactive GnRH analogues. The only GnRH available in India is from the brain of a freshwater murrel, Channa punctatus. Combination of two murrel GnRH variants, GnRH I and GnRH II, produces far more superior effects than "Ovaprim". Biotechnology input in fish breeding is no doubt highly appreciable as it provides the cultivators almost a riskless method. However, research in different laboratories is still in progress to have a more potent molecule with the possible addition of some metabolic hormones. Pisciculture is now a booming industry all over the world, which imposes a larger demand for "Ova prim" like products. Murrel GnRH, therefore is expected to be a highly competitive product in the global market