Presented by: SUSAN ANN JAYAN II M.Sc., BiotechnologySchool of Biotechnology & Genetic Engineering Bharathiar University
NEED FOR AQUACULTURE Worldwide per capita fish consumption nearly doubled from about 8 kg in the early 1950s to about 15.8 kg in 1999 Fish exports from the developing countries have surpassed export of traditional crops in meat Presently, the Indian fisheries sector accounts for an annual turnover of over Rs. 220 billion, which is 1.40 percent of total GDP and 4.6 per cent of agricultural GDP (Pillai & Katiha, 2004).
The fisheries sector plays a vital role in the Indian economy, by addressing various issues like food and nutritional security, employment, livelihood support and socio-economic status and fishing communities The depleting resources, energy crisis and resultant high cost of fishing have led to an increased realization of the potential and versatility of aquaculture as a viable and cost-effective alternative to capture fisheries.
WHAT IS FISH GENETICS ? Fish genetics has been broadly defined as, Application of genetic principles and methods for increasing aquaculture productivity by genetically modifying living aquatic organisms or part of theseorganisms and for management of wild fish populationsto obtain maximum sustainable yield without affecting genetic diversity
APPLIED GENETICS FOR IMPROVEMENT OF GENETIC STOCKS Selective Breeding for faster growth & disease resistance of cultivated fish ‘Jayanti rohu’ (CIFA-IR-1), a variety of rohu has been successfully developed after four generations of selective breeding, under Indo-Norwegian collaboration (AKVAFORSK; funded by NORAD) during 1992-2000 at CIFA, Bhubaneswar Penaeus monodon (tiger shrimp), Cyprinus carpio Manipulation of live feed size By bidirectional mass selection of Artemia franciscana (6 generations) for smaller naupliar size
Transgenic fish Rapid and efficient method for fish improvement across a wide range of species by direct gene manipulation First aquatic GMOs were the Rainbow trout and Gold fish Most popular gene has been ‘Growth hormone’ of fish origin, for bigger size ‘Glow fish’ created using fluorescence genes from jellyfish, for ornamental multi-colored glow As ‘bio-reactors’ for production of pharmaceuticals First Indian transgenic Zebra fish was created at Madurai Kamaraj University, Tamil Nadu
DNA Vaccines for fish An example is the injection of Atlantic salmon with a DNA sequence encoding infectious hematopoeitic necrovirus (IHNV) glycoprotein under the control of cytomegalovirus promoter (pCMV). Eight weeks after the challenge with the virus, significant degree of resistance had been achieved. The fish were still resistant and were shown to have generated antibodies three months later
CHROMOSOMAL MANIPULATION In externally fertilizing fishes 1. Gynogenesis Induced gynogenesis involves inactivating the paternal (sperm) genome and then restoring diploidy either through suppression of the second meiotic division (“meiotic” gynogenesis) or suppression of the first mitosis (“mitotic” gynogenesis). Most of the more recent protocols for gynogenesis have used ultraviolet irradiation to inactivate the paternal genome, and temperature (cold or heat) shocks to restore diploidy.
The various applications of gynogenesis are chromosomal mapping, inbreeding with homozygosity and generation of mono sex population. Among Indian major carps, gynogenesis has been induced in Labeo rohita Gynogenesis combined with sex reversal of female into male involving the use of male hormones is a practical method for improvement of species to produce faster growing individual as well as for incorporation of other advantageous traits
2. Androgenesis Androgenesis is the method of reproduction where only the paternal genome is contributed to the offspring. Androgenesis can be induced by the destruction of female nuclear genome before fertilization using UV rays and fertilizing it with normal sperm. Androgenesis is useful in producing inbred lines. In conjunction with sperm cryopreservation method, androgenesis may prove useful in conservation programme when females of a species are not available. Androgenesis has been investigated less than gynogenesis and survival of androgenic individuals is much less compared to gynogens as the cellular organelle of egg will be affected during irradiation
3. Polyploidy By chromosomal stimulation it has been possible to obtain haploid, triploid and tetraploid fishes. Triploidy is induced by second polar body retention and tetraploidy from first mitotic interference, followed by subjecting the egg to a pressure or temperature shock shortly after fertilization. Among better-known fish, direct induction of triploidy has been induced in common carp and grass carp. Triploid grass carp produced by cold and heat shock is an effective weed consumer but being sterile there is no risk of multiplication.
Crosses between diploid and tetraploid brood stock can produce triploid offspring without the need to induce triploidy but the production of tetraploid brood stock is very difficult in most species where this has been attempted (very low larval viability; poor fertility in females: Pandian & Koteeswaran, 1998)and fertilization rates in diploid female X tetraploid male crosses are also low, probably because of the large size of the sperm (Padhi & Mandal, 2000). Triploidy could at least in theory be used anywhere to control reproduction of alien species, domesticated strains, transgenic fish, etc., and is already used in commercial aquaculture in a limited range of species. These fishes are likely to be sterile and would hopefully grow faster by avoiding the process of gametogenesis which is wasteful in fish farming.
4. Sex control The mono-sex fish culture is advantageous where one sex grows bigger than the other sex or sterile population is economical in fish farming by conversion of ingested food energy into flesh with minimum wastage of energy in to gonadal maturation. About 20 per cent of total ingested food energy is used in reproduction which can be channelized in production of fish flesh. Sex steroids being primary inducers of various reproductive phenomena, there is ample scope for reproductive manipulation of sex. Adequate application of either androgen or estrogen to the juveniles overrides the intrinsic sex determining mechanism and directs it either in a male or female direction or induces sterility without altering the genotype.
CONCLUSION In India, fisheries science has witnessed a moderateresearch activity on genetics and its allied areas in the lasttwo decades. Future of genetics research with respect toaquaculture development and fisheries management ispromising, notwithstanding some technical problems, whichstand in the way of its commercialization. A lot moreresearch efforts are needed in this area to generate processand products of applied interest in aquaculture and capturefisheries management. Fundamental research using molecular markers willlead to a better understanding of genetic structures of wildpopulation. This can lead to improved management ofspecific fisheries and selective breeding programmes, butwill also lead to a greater ability to catalogue and bettermanage fish diversity.