Fish Breeding and Genetics PDF

FISH GENETICS AND BREEDING Terms: 1.Gene- contain the genetic material by which hereditary characteristics are transmitted 2. Allele- the mutational variations of a gene that can occur at each locus 3. Hybrid- trait that was derived fr...

FISH GENETICS AND BREEDING Terms: 1.Gene- contain the genetic material by which hereditary characteristics are transmitted 2. Allele- the mutational variations of a gene that can occur at each locus 3. Hybrid- trait that was derived from two different alleles 4. Mutation- an abrupt and permanent change in the genetic material 5. Homozygous- a trait determined by two identical alleles at the same locus, resulting in a true breeding strain for that trait 6. Heterozygous- a trait determined by two different alleles at the same locus, resulting in a hybrid angelfish that will not breed true for that trait 7. Recessive- different alleles occur at the same locus and one of the alleles is not expressed in the presence of the other 8. Dominant- different alleles occur at the same locus and one of the alleles is not expressed in the presence of the other 9. Phenotype- physical appearance of a trait 10. Genotype- written expression of the genetic makeup of the trait 11. Variety- Any of a group of widely separated variants within a single interbreeding population 12. Strain- descendants of a common group within a variety 13. Inbreeding- breeding technique to fix traits known to a particular line of angelfish. This involves the mating of closely related fish, i.e. brother to sister, father to daughter. 14. Line-breeding- mating of related fish, i.e. brother to grandmother, father to cousin, etc. crossed to each other every 3rd or 4th generation 15. Out-crossing- breeding technique of using unrelated parents Teleosts - bony fishes Elasmobranchs - sharks and rays Gonochoristic - separate male and female  Hermaphroditism – present of male and female organs a. synchronous b. sequential i. protagyny- male to female ii. Protandry- female to male Spermatogenesis- development of sperm Oogenesis-development of ova RESEARCH ON TILAPIA Genetically Improved Stocks (as of date) 1. Genomar Supreme Tilapia 2. Genetically Improved Farmed Tilapia (GIFT) 3. Freshwater Aquaculture Center Selected Tilapia (FAST) 4. Genetically Enhanced Tilapia-Extra-Large, Excellent (EXCEL or GET-EXCEL) 5. SEAFDEC-Selected Tilapia (SST) 6. Genetically Male Tilapia (GMT) or YY-supermale tilapia 7. SaltUNO or Molobicus (hybrid from a Nile and Mozambique tilapia cross) SEX REVERSAL -Mix sexes in the pond causes the over-population of the stocked tilapia in ponds and the stunted growth of the fish -with mixed-sex tilapia stocks, the sizes of the harvested fish vary from small to large because of the difference in the growth of the faster-growing males compared to the females Techniques 1. hand sexing -separating the males and females manually 2. hybridization -mating of two species to produce all-male offspring 3. artificial sex reversal - most efficient and less expensive Artificial sex reversal - Feeding of synthetic sex hormones (e.g., methyltestosterone) to sexually- undifferentiated fry. feeding newly hatched tilapia fry with special hormone treated food for 3-4 weeks Manipulation of sex-ratios in tilapia 1. Hybridization 2. Hormonal application a. Direct- fry are treated with hormones during sexual differentiation to change sex ratio -Application of 30-60 ppm 17-α Methyltestosterone -Applied 10 days after post hatch (swim-up stage) and sexually undifferentiated b. Indirect- sex determination system is manipulated in broodstock to result in progeny which are all genetically same sex  -development of YY males or ZZ females 3. Temperature dependent sex-determination -34-38°C can change phenotypic sex (female to male) YY MALE TECHNOLOGY -combining feminization and progeny testing, to produce novel males with YY genotypes (i.e. with 2 male sex chromosomes) instead of the usual XY male genotype -supermales and have the unique property of siring only male progeny. -are as viable and fertile as normal males, can now be produced in large numbers and are being used commercially to mass produce high yielding GMT for tilapia growers in the Philippines GENETICALLY MALE TILAPIA (GMT) -the all-male progeny of YY males -are normal XY males (although some can “naturally” revert to female, giving GMT an average sex ratio of >95% male) -produced higher yields, through a combination of enhanced survival and faster growth rates -higher yields were accompanied by lower food conversion ratios (FCR) and greater size uniformity, factors which also contributed to the improved profitability of culturing GMT compared to present available stocks. MOLOBICUS -cross breed of Oreochromis mossambicus and O. niloticus *direct transfer to saline environment (20-35 ppt) in 96h to determine the most segregating salinity -salinity is increased daily (6ppt and 3ppt) Results: -hybrids are more saline-resistant than O. niloticus -hybrids and O. mossambicus have the same tolerance in salinity -M and F hybrids grow faster than O. mossambicus -M and F hybrids the grow in O. niloticus  BREEDING GENETICS OF FISH BROODSTOCK 1. Too much domestication and bad breeding (brother/ sister/ cousin spawning) and too few broodstock gives bad broodstock quality 2. Mixing different stock and using genetically improved strains improves the health of broodstock and the fry and fingerlings that are produced from them RECOMMENDATIONS FOR KEEPING HEALTHY BROODSTOCK 1. Use of atleast 50 broodstock (100-200 is better) or mix smaller numbers of different strains 2. Broodstock come from different families or a mixture of strains 3. Use of equal numbers of male and female broodstock 4. Hatchery spawning as is better than pond spawning 5. Replace broodstock regularly with genetically improved strains or the best growing fish from the ponds of different farmers