4 - Central Institute of Brackishwater Aquaculture

National Workshop-cum-Trainlng on BiOinf~rmatlCS and Infonnafon Management in Aquacukra
genetics study to determine different parameters used in the selective breeding
programme.
2. Selective Breeding
The potentials of genetics have already exhibited promising trends in aquaculture
too. The correct breeding procedures followed through selective breeding in the
case of Atlantic salmon and rainbow trout in Norway, Channel catfish in USA and
Nile tilapia in Philippines are the standing examples in this regard (Gjedrem,
1997). The recent selective breeding programme of rohu (Labeo rohita) in India too
isanotherexample of the kind (Reddy etal., 2002).
Before success of induced breeding through hypophysation in late fifties rivers
are the main source for seed collection of Indian major Carps. With the
introduction of induced breeding technique, hatcheries have been able to
produce enough quantity of carp seed. The hatcheries in India hardly follow any
genetic norms to produce carp seed. A limited number of brood fishes are used
repeatedly for successive generations. As a result the quality of carp seed is
showing negative effect of inbreeding i.e, slow growth rate, disease proneness
etc.
Inbreeding
Inbreeding occurs due to mating of closely related individuals. Genetically
inbreeding leads to homozygosity. Almost all individuals carry deleterious
recessive genes, which are hidden in heterozygous state. Related individuals are
likely to share common genes and probability of pairing of deleterious recessive
genes gets enhanced with the increase of closeness between the parents. Due to
which inbreeding depression occurs to the population with decrease growth
efficiency, disease resistance and survival.
Effective population size
Effective population size is one of the most important concepts in the
management of a population in that it gives an indication about the genetic
stability of the population. It depends upon several factors such as total number
of breeding individuals, sex ratio, mating system and variance of family size. The
effective population size can be calculated by following formula,
Where N.= Effective population size
Nf = Number of female brood fishes used for seed production
N,= Number of male brood fishes used for seed production
Effective population size is inversely related to inbreeding