The steadily growing importance of culture fisheries has made it imperative that the practical fish culturists improve the techniques necessary for securing the initial and basic requirement of fish culture; namely, the production of young fish for stocking. Fish culture today is hardly imaginable without the artificial or semi-artificial mass propagation of fish seeds of cultured fish species. The need for production of quality fish seed for stocking the artificial ponds and natural water bodies has been steadily increasing. It is evident that but for the well-known techniques of artificial propagation and induced breeding, the trout streams would be largely without trout and the yield from fish ponds could only be modest at best. It can be further stated that artificial propagation methods constitute the only practicable means of providing enough quality seed of the river-spawners for rearing in confined waters such as fish ponds, reservoirs, lakes, etc.
Artificial propagation techniques have made possible the mass supply of seeds for large varieties of fishes for culture in ponds and other enclosed water bodies, as well as for superintensive culture systems (e.g., cage culture, raceway culture, pen culture, etc.). These techniques have also made it possible to introduce several important species of fishes at widely separated geographical areas.
There are many fishes which would be excellent for culture if only the problems related to mass propagation of seeds could be solved. Present research activities on the improvement of induced propagation technique hold great promise. Some of the new species drawn into the culture systems may prove to be very useful to increase fish yield per unit area.
The possibilities of obtaining quality fish seed in adequate numbers from natural sources are rather limited. Therefore, even the species which reproduce successfully in confined waters are propagated artificially. Apart from being able to obtain quality seed, the artificial propagation technique can also be used to develop strains superior to their ancestors by the methods of selective breeding and hybridization. The hypophysation technique has revolutionized quality fish seed production and provides great opportunities for the development of inland fisheries, in general, and aquaculture, in particular, in areas where fish production by aquaculture were considered to be impossible.
The artificial propagation technique permits the incubation and hatching of eggs and the rearing of seeds under well-protected and weather-independent conditions. Depending on the perfection of the system, 10–70 percent of the eggs produced can be raised to viable fingerlings. As against this, the survival rate in natural spawning is generally much less than one percent of the eggs produced.
Induced propagation technique also makes it possible to obtain out-of-season supplies of fry and fingerlings. This technique also provides the easiest tool for improvement of the stocks of cultivated fishes, whereby fast growing, disease-resistant, temperature-tolerant, and tasty strains can be selectively raised. Further, this technique can be used for producing intraspecific, interspecific, and intergeneric hybrids of more culturable qualities than were their parents. It is also useful in breaking the “parasite-chain”, by which parasites from the parents are transferred to the offspring. The egg, larvae, fry, and fingerlings produced through artificial propagation technique can be easily transported great distances with reduced threat of transmitting disease-causing organisms or of transporting unwanted fish species.
The biggest constraint in fish culture is the lack of quality fish seed in adequate quantities. This shortage of fish seed is impeding the extension and expansion of fish culture throughout the world. It is hoped that this manual will contribute substantially to mitigating this situation.