Abstract
A series of experiments were conducted to identify and propagate YY supermales of tilapia
from YY paternal stock collected from Central Luzon State University of Philippines. At first,
10 fish were bred individually with normal females (XX) and nine fish were identified as
putative YY males which produced 86.7% to 99.0% male progeny. Four putative YY males were
bred separately with normal females (XX) and the produced XY fry were feminized with
200mg of ẞ-estradiol per kg of feed which produced 93.4% to 98.0% females. These ẞ-estradiol
treated females were reared upto maturity and 24 of them were bred individually with normal
males (XY) and 17 were identified as XY sex reversed female which produced 67.5% to 85.4%
male progeny. Then six identified XY females were mated separately with identified YY males
and the produced fry (XY, YY) were feminized with 200mg ẞ-estradiol per kg of feed which
produced 92.2% to 98.1% females. These ẞ-estradiol treated females (mixture of XY and YY
females) were reared upto maturity and 29 of them were bred individually with normal males
(XY) and 8 were identified as YY female. Then three identified putative YY supermales were
bred individually with three identified YY females which produced 98.6% to 100.0% male
progeny and the resultant progenies were considered as YY supermale broodstock. A total of
21 YY supermales from this broodstock were bred individually with normal females (XX) to
produced genetically male tilapia (GMT), 18 of them were identified as putative YY males that
produced 81.6% to 100.0% male progeny and the resultant progenies were considered as GMT.
The growth, survival and production performance of GMT derived from YY males were
compared with sex reversed tilapia (SRT) fry produced through masculinization with 17amethyltestosterone and mixed sex tilapia (MST) in six earthen ponds with a stocking density of
100 fish/decimal. Fry were fed with supplementary feed containing approximately 30% crude
protein. The initial weight of GMT, SRT and MST was 5.45±0.35g, 4.35±0.35g and 4.70±0.50g,
respectively. Over the culture period of 105 days, the weights of GMT, SRT and MST were
found 193.21±3.07g, 176.36±0.94g and 154.82±2.57g respectively and the performances were
significantly different (P<0.05) from each other. The survival rate of GMT, SRT and MST was
91.68±1.35%, 87.38±1.38% and 88.16±0.73% respectively and they were not significantly
different (P>0.05). The net production of GMT (4252.77±124.06 kg/ha) was significantly
(P<0.05) higher than that of SRT (3712.56±71.46 kg/ha) and MST (3269.40±72.01 kg/ha). The
result of the economic analysis showed that the net profit of GMT, SRT and MST fish were BDT
0.119±0.007 million, BDT 0.066±0.003 million and BDT 0.029±0.003 million respectively. The net
profit of GMT fish was significantly (P<0.05) higher than that of SRT and MST. The
development of cryopreservation protocol for YY supermale of Nile tilapia Oreochromis
niloticus, entailed a number of experiments. The concentration of sperm ranged from
3.44×109 to 4.40×109 cells/ml. Activation of sperm motility decreased with increasing
concentration of the extending media and motility was severely inhibited at 1.0% NaCl. The
toxicity of cryoprotectant (DMSO and methanol) to sperm was tested at different
concentrations (5%, 10%, 15%) and incubation time (5-20 min). Cryoprotectants with 5% and
10% concentrations produced better motility during 5 and 10 min incubation. Two extenders,
Alsever's solution and Modified Fish Ringer, and two cryoprotectants, DMSO and methanol
were used for cryopreservation of sperm. Alsever's solution with 10% DMSO showed best
performance producing 81.7±1.7% and 53.3±3.3% equilibration and post-thaw motility respectively. Between two diluents, sperm preserved with Alsever's solution plus DMSO
produced 36.66±2.32% and 16.20±1.84% fertilization and hatching while fresh sperm yielded
74.34±4.39% and 60.25±5.30% fertilization and hatching rate respectively. The protocol
developed through the study can be applied for long-term conservation of genetic materials of
sperm of the YY supermales of Nile tilapia Oreochromis niloticus and the cryopreserved sperm
can be used in artificial breeding for generating new individuals.