Abstract:
Growth performance of Genetically Improved Farmed Tilapia at three
different stocking densities (50, 75 and 100 fish m-3
) in triplicates were
evaluated in a cage culture unit of nine cages established in a perennial
reservoir in Hambantota District. Nylon material having mesh size of 10 mm
recommended for cage culture was used. Fingerlings (6750) were stocked in
nine cages, fed with a formulated diet according to the body weight using
feeding trays. Monthly samples from each cage were weighed and the study
conducted for four months. In all cages, monthly mean weight increase was
very low. Cages with low stocking density had the highest weight gain while
high density had the lowest. Specific growth rate (SGR) in fish of all nine
cages increased in the first month and then gradually decreased during
subsequent months. Wild fish (Puntius dorsalis, P. singhala, Rasbora
daniconius, Devario malabaricus, Glossogobius sp., Esomus sp.) entered
into cages in large numbers had contributed to decrease in SGR. Highest
weight of the wild fish was recorded in the second month and reduced in
subsequent months due to regular inspection. Effective increase in SGR
however was not observed. In two cages having 100 and 75 fish m
-3
showed
an increase in SGR in last two months which was not observed in other
cages. This effect relates with the changing of the water current in the
reservoir into opposite direction resulting water entering firstly into these
two cages making a rapid increase in fish weight. Awareness of changing
water current patterns in the reservoir and positioning the cages accordingly
is an important issue to be considered in commercial cage culture. Use of
5mm mesh size is recommended to avoid wild fish invading the cages and
has proven a good harvest.
