| Abstract | This study was conducted to assess the growth performance of different sex genotypes
(XX and XY) of Nile tilapia (Oreochromis niloticus) and effects of the synthetic androgen
(17a-methyltestosterone, MT) on the growth during September 2000 to April 2001. The
experiment consisted of three stages, namely, the fry treatment stage, nursing stage and growout stage, and was carried out in hapas suspended in earthen ponds. There were six treatments
in triplicate: (A) genetically female tilapia (GFT), (B) genetically male tilapia (GMT), (C)
mixed-sex tilapia (Mixed), (D) MT-treated genetically female tilapia (MT-GFT), (E) MTtreated genetically male tilapia (MT-GMT), (F) MT-treated mixed-sex tilapia (MT-Mixed).
During the grow-out stage, an additional treatment was included: (G) tagged MT-GFT plus
MT-GMT in 1:1 ratio. All experimental ponds were fertilized weekly with urea and triple
superphosphate at rates of 28 kg N and 7 kg P/ha/week, and Nile tilapia were fed artificial
feeds during the entire experimental period.
During .the fry treatment stage, results showed that MT-GFT grew significantly faster
than other tilapia groups (P< 0.05), among which there was no significant difference in
growth (P> 0.05). However, survival was lowest in MT-GFT, and was significantly lower
than that in GFT, GMT and MT-Mixed (P< 0.05), but not significantly different from that in
MT-GMT and Mixed (P> 0.05). Among all tilapia groups except for MT-GFT, there was no
significant difference in survival (P> 0.05).
During the nursing stage, the highest growth was found in MT-GFT, intermediate in
the rest of MT-treated groups, and lowest in control groups (P< 0.05). Growth in MT-treated
groups was significantly higher than that in the respective controls (P< 0.05), while there was
significant difference in growth among the controls (P> 0.05). Survival rates were high in all
treatments without significant differences (P> 0.05).
During the grow-out stage, MT-GFT also showed the highest growth, followed by
MT-Mixed, which grew significantly lower than MT-GFT but significantly higher than other
treatments (P< 0.05). Growth in MT-GFT and MT-Mixed was significantly higher than that
in their respective controls, GFT and Mixed (P< 0.05), while there was also no significant
difference in growth between MT-GMT and GMT (P> 0.05). Growth of GFT was not
significantly different from that of GMT (P> 0.05), but these two groups were significantly
higher than that of Mixed (P< 0.05). Survival rates were also high in all treatments without
significant differences (P> 0.05). Results also showed that there was no significant difference
in growth between MT-GMT or GMT cultured alone and communally (MT-GMTinix or
GMTinix) (P> 0.05), however, MT-GFT or GFT cultured alone grew significantly faster than
that cultured communally (MT-GFTmix or GFTmix) (P< 0.05).
The present experiment indicates that anabolic responses were not observed in male
Nile tilapia, but observed in female Nile tilapia. Results also showed that MT-treated mixedsex grew significantly faster than genetically male tilapia. The best growth performance of
MT-treated female Nile tilapia may lead to an alternative method to produce all-male tilapia,
however, more research in large-scale is needed. |