annual report - Central Institute of Brackishwater Aquaculture

A selective breeding experiment was
conducted with three size groups of P.mono-
$on from three different mothers, to identify
strains with disease resistance and faster
growth. In order to rule out variationsdue to
environmental factors all the animals were
grown in identical conditions and the
RNAlDNA ratio was periodically estimated
from the three groups. Larger animals from
3 mothers were shown to possess greater
RNA/DNA ratio compared to smaller animals.
Preliminary experiments conducted on
disease resistance, indicated that larger animals
exhibited better disease resistance compared
to smaller animals.
Studies on genetic manipulation for
molecular sexing were initiated in the
seabass Lates culcati~er. As a fit step, the
technique of preparing metaphase chromosomes
was standardised. 'Ihe chemical colchicine
was injected into the fish (1
rng~mI/l~ bodyweight) and blood samplks
were collected and processed to obtain metaphase
chromoso&s. Work is in progress to
separate nucleii and prepare blocks for pulse
field electrophoresis.
Cryopreservation of milt was carried
out using the milt of grey mullet M, cephalw
diluted in the extender Fish Ringer and cryoprotectant
5% dimethyl sulphoxide
(DMSO). lhe cryoprese~ved milt was tested
periodically for motility estimation. The samples
showed a post-thaw motility around
50%.