Fish Breeding and Biotechnology

Abstract

In this review four different methods which have been used for cultivating new breeds of fish of agricultural importance are discussed. They are; 1. Natural and artificial selection, 2. Artificial sexual hybridization, 3. Nuclear transplantation and 4. Gene transfer. Among them, natural and artificial selections and sexual hybridization are traditional, sexual and non-biotechnical methods. They are popularly and successfully used in fish farming practice in the history. But their further application is limited because of the difficulties of composition of sexual combinations between distantly related species. Furthermore identification and composition of the characteristics which are to appear in the hybrid fish presents many problems. Nuclear transplantation and gene transfer are two newly developed methods for attempting to cultivate new breeds of fish. Biotechnology thus offers the chance of transferring genetic materials or molecules between different fish species. It is expected that these two methods will ultimately replace the sexual methods for obtaining more stable, predictable hybrid fishes. Because no species-specific limitation will appear in those genetic transfer combinations and the target genes which were the newly developed fish in unique ways. Some important approaches have already been made in those research areas, but some special problems, theoretically or technically , have to be solved before those biotechnical methods can successfully be applied to fish culture on commercial scales. Review Article In the literature several kinds of methods which have either already been applied or are intended to be used for cultivating new breeds in animals of agricultural importance have been recorded. These include : I. Natural and artificial selection To artificially select of better animals from naturally existing animal species is one of the traditional methods for this purpose. Those selected animals represent mutants accumulated in long-term natural environmental situation. Their characteristics were successfully modified. Through sexual breeding among those individuals , they produced offsprings generation by generation and finally some new breeds, varieties or species of those animals were obtained. This represents 'domestication'. Since the frequency of natural mutation is very low and to obtain new breeds or varieties will usually take a long time of evolution history. For example, when the same species of animal distributed in different areas were influenced by the different local environmental factors for a long time, firstly some of them and their