Aquaculture Articles on Genetics, Breeding and Reproduction
Pacu (Piaractus brachypomus), a native fish of South America recently introduced as an alien species into India via Bangladesh. A tendency has been observed among the fish breeders of Bengal to raise seeds of alien species, principally those that are carnivorous. Besides breeding individual species, the fi sh breeders are also interested in conducting hybridisation programmes between Indian major carps and exotic species, as they are largely unaware of the genetic consequences of such activities.
Sturgeons usually do not breed naturally in captivity and must be spawned artificially using exogenous hormones. The timing of their migratory spawning behavior (e.g., upriver migration from the ocean), presence of ripe fish in the spawning grounds, and external appearance of the brood fish have traditionally been used to assess the stage of maturity and specific time of spawning. However, assessment of ready to spawn (ripe) sturgeon based simply on behavioral and external sex-limited characteristics can be misleading especially in domestic stocks that are raised under aquaculture conditions, as they are not exposed to natural conditions that promote sexual maturity and serve as spawning cues. Selection of female fish for spawning without proper assessment of their stage of egg maturation often results in partial or no ovulation, or ovulation occurs but with low egg fertility or low embryo survival. Many factors influence ovulation and spawning success in farmed sturgeon, from temperature and light regimes, husbandry methods, handling and transport, induced spawning protocols, and genetic make-up of the stock. However, relatively simple field and laboratory tests can be used to assist in predicting ovulatory response in female sturgeon. The simplest and most reliable indicators that a female is ready to spawn are egg size and the position of the egg nucleus in the cytoplasm, referred as the egg polarization index or PI.
Publication of the human genome draft sequence (Lander et al., 2001; Venter et al., 2001), and those of other species represent major milestones in scientific discovery. This genomic unraveling has helped identify the functions of numerous unknown genes and, in certain cases, has assisted in determining the roles of specific genes in disease processes. The genomic revolution incorporates much more than the decoding of organismal genomes alone, however. Critical to the success of this field have been like innovations in molecular and cellular biology, information technology, analytical sciences and in automation (Witkamp, 2005).
Introduction: transgenic vs enhanced selection
Aquaculture, like agriculture, is beset with problems of cost, price, and risk. Genetic research, in aquaculture as in agriculture, promises – or dangles – solutions to many of these problems “real soon now”. But what kinds of solution? Investors as well as farmers soon notice that there are two, competing styles of modern genetics, which in this paper are loosely termed “transgenic” and “enhanced selection”.