Successive choosing of the best varieties from the availablelot by nature or man.The aim of a breeder - to get maximum profit possible the genetic worth of the stock by selection.Based on a single desirable trait or combination of traits.
growth rate, by better utilization of food natural food in ponds ; food mixtures resistance to deviations from the normal environmentalconditions - oxygen deficiency, high or low temperature, higher salinity etc resistance to infectious diseases to infestation with parasites the nutritive properties of fish.
1. Specifically define - the breeding goal i.e. the trait under selection2. The entire life cycle of the animal should be under control.3. It should be possible to hold and individually evaluate a number of generations in identical rearing systems.4. Establish relative economic value of the traits that are to be selected5. For the selected traits, the phenotypic (VP) and genetic variances (VG), heritabilities etc should be known. VP = VG + VE
Mass selectionGenotypic selection Family selection Sib – selection Selection by progeny testingCombined selection
• Character/ Individual selection• Individuals selected from mixed population on the basis of phenotype.• Genotype may be unknown.
Response (R) = i x σ x h2 = S x h2• i = intensity of selection• = degree of variation in the trait• h2 = heritability• S = Selective differential• Response α heritability• h2 = R/S
METHODS TO RESPONSE• i / σ / h2• ↑ intensity of selection(i) ↑ no. of individuals grown → ↑ severity of selection• Variability (σ ) ↑ only genetic variation important envtal - useless - ↓ heritability
Heritability ( h ) 2• Outbreeding – cross non related individuals → ↑degree of heterozygosity i.e. ↑ in genetic variation• Inbreeding ↑ homozygosity
ADVANTAGES OF MASS SELECTION• Simplest & common method• Characteristic to be improved easy to measure• Can be used efficiently in selection for growth rate for age at maturity
• To overcome disadvantages of mass selection• include – family selection progeny testing
• For selection of characteristics of low heritability - survival, meat quality, age at maturation• Families grown in identical conditions ↓ Compare & select best
Response eq. ~ mass selection ~• Rf = if x f x h2f• i < mass selection – not possible to grow large no. of families.• reduction in - denotes variation in family not individual variation• h2 much higher
• If individuals from best family sacrificed for examination – use brothers & sisters for breeding• Use full & half siblings• Advantage – generation interval not ↑ like mass selection• Disadvantage – each family - separate tank - marking difficult - envtal & tank effects on characters b/n families.
• Enables assessment of breeding qualities of separate spawners/pairs of spawners & selection of best• 3 methods I.Testing pairs (not separately) II. ,, spawners of one sex III. ,, both ♀♀ & ♂♂
Advantage of PT• permit evaluation of separate spawners & selection of best
• Mass selection more efficient• Genotypic selecton advantageous for certain characters – fat content• For characters like weight – combined selection• CS sum up efficiencies of mass & genotypic selection in short time.
CS consist of:• Performing mass selection amoung fingerlings• Progeny testing of males• Family selection with simultaneous breeding of 5-10 families• Repeated performance of mass selection in the best families
It is the technique of breeding of fishes of two species or genera whichordinarily do not breed.Fish - external fertilisation - Fish hybridizes more frequently thantetrapodesNaturally hybridized fishes - Cyprinidae , Salmonidae etcHybridization - ↑ hybrid vigour / heterosisHybrids – fertile/sterile – must be verified before introducing to naturalenvt.Indiscriminate hybridization → contamination of genepool.Interspecific & intergeneric hybridizations
INTER SPECIFIC HYBRIDIZATION female Labeo calbasu Labeo rohitaproduced by mating between two different species in same genus.In India mating female kalbasu and Labeo rohita was highly successful.Over 94% fertilisation was obtained.The growth rates of hybrids are superior to the parent Kalbasu.It attains maturity in two years.
INTER GENERIC HYBRIDIZATION• male and female are selected from different genera• Catla catla Labeo rohita• Inter generic hybrids between Catla and Rohu attains full maturity in 3yrs.
Intergeneric hybridization Labeo rohita Cirrhinus mrigalaCrossing between Rohu and Mrigal is more successfuland 90% fertilisation is done andhybrids attain full maturity in 2yrs andshowed intermediate character
Intergeneric hybridization Cirrhinus mrigala Labeo calbasuMrigal-Kalbasu hybrids attain full maturity within 2-3yrs.These hybrids are also capable to produce new ones.
• In fish farming, if proper care is not taken the fishes can breed with their close relatives or same parental generation – INBREEDING• cause early mortality of fish, poor growth rates and other genetical abnormalities – INBREEDING DEPRESSION• Inbreeding →reduction of desirable traits and fertility.• If a farm based on limited number of population of brood stocks the progeny over long periods can face inbreeding problems.
The advantage of inbreeding:• Production of inbreed lines are useful in improvement of stock• To produce pure lines of fish Pure lines of strains are used for perfect hybridization of fish to obtain favourable heterosis, monosex. · Pure lines help in gene mapping· To determine 1. Phenotypical variations 2. Extent of inbreeding depression 3. chromosomal makeup to the fish
Crossbreeding is the solution of inbreeding depression, the fishes are allowed to breed with different breed varieties, strains orgenotypes of farmed speciesthe aims of cross breedingto achieve· Better growth rate· Better desired qualities· Increase the survival rate• lower the early stage mortality
· By chromosomal manipulation – Gynogenesis or Androgenesis· Hormonal manipulation – Feminisation or Masculisation· By genetic engineering – trangenesis or mutation
Gynogenesis• process to produce individuals from maternal chromosomes only eventually to obtain homozygosity.• Parthenogenetic devpt of eggs after activation with genetically inert sperm• Gynogenesis in fish farming is used to form inbred lines to achieve proper hybridization and selective breeding. Methods: Sperm nucleus is inactivated prior to fertilization by use of X-Rays, chemicals – dimethyl sulphate.• eggs are exposed to sub lethal temperature shocks before or after fertilization - suppress the meiotic divisions of eggs i.e. ensuring the non reduction of nuclear components.• Upon fertilisation the resulting diploid individuals retain the second polar body nucleus (maternal) besides the egg nucleus,
gynogenesis- preventing the extrusion of second polar body Activation – irradiated sperm Egg Shock treatment and retention n of 2nd polar body n 2nd polar body Homozygous diploid 2n Gynogenetic progeny •In India Gynogenesis are tried on Indigenous as well as Exotic carps. •Eggs of rohu are fertilised with irradiated sperms of Catla and then exposed to cold 12°C and heat 39°C shocks to obtain gynogenetic rohu.
ANDROGENESIS• Development of an organism with only paternal genes• androgenesis is development of an embryo from a fertilised egg from which the nucleus has been removed.• The embryo therefore contains only paternal genes.
The method of dispermic androgenesis, developed androgenesisfor sturgeon fishes, includes genetic inactivation ofeggs, their insemination with concentrated sperm (tocause polyspermy), and heat shock to facilitate thefusion of male pronuclei.The restoration of the diploid state of androgenotesby fusion of two sperm nuclei allows androgeneticprogeny to have a heterozygosity level similar to thatin a regular crossing. endangered sturgeon fishes may be recovered bymeans of dispermic androgenesis if the sperm aloneof a given species is available.
Mono Sex CultureMono-sex culture is based on the culture of fish byproducing all males or all femalesdepending upon the sex which have better foodconversion ratio and growth rate.Experimental hybridization in Tilapia can producemonosex stockTreatment with sex hormones : sex reversal
Necessity of Monosex Culture Some time one sex of certain species has better growth rate and food conversion efficiency.To culture that sex (male/female) monosex culture is essential.For example - male Tilapia grows faster than female -culture of male is beneficial in case Tilapia.
Transgenic Fish• A transgenic fish is one which carries one or more than one foreign genes.• The foreign genes are selectively incorporated by micro injection into the egg → transgenic fish.
• Fish transgenies are difficult because of tough egg-chorion which impedes microinjection.• A prior puncture or use of micro pile (an opening in the egg surface for sperm entry during fertilisation) has to be made for microinjection.• The micropile is made by or by using trypsin digestion.• The gene can be transferred by electroporation (exposing the egg chorion in an electric shock for a fraction of second) or by retroviral injection.• The foreign gene then transferred into the nucleoplasm or the cytoplasm.• In case of retroviral injection, the genes are first incorporated into the viral genome, and then through the virus the gene are transferred into the host by injection.
• · The fish of superior quality or desired traits are produced by this process.• Giant sized fish or super fish can be produced.• This can be achieved by incorporating the growth promoting genes – bovine growth hormone gene or human growth hormone gene
GENETICALLY MODIFIED ROHUCentre for Cellular and Molecular Biology (CCMB)CCMB fish are auto-transgenic, meaning the genes inserted into afish’s genome are a mashed-up cocktail of its own genome. not importing genes from an alien species, not using DNA from even arelated species.There are no foreign genes involved. Therefore, it’s unlikely that meregenetic modification could produce a toxic protein,the synthesized gene stimulates production of a growth hormone thatmakes the fish bigger and grow faster,