monosex production of tilapia, oreochromis niloticus using ...60 z.a. el-greisy, a.e. el-gamal....
TRANSCRIPT
Egyptian Journal of Aquatic Research (2012) 38, 59–66
National Institute of Oceanography and Fisheries
Egyptian Journal of Aquatic Research
http://ees.elsevier.com/ejarwww.sciencedirect.com
FULL LENGTH ARTICLE
Monosex production of tilapia, Oreochromis niloticususing different doses of 17a-methyltestosterone with respect
to the degree of sex stability after one year of treatment
Z.A. El-Greisy *, A.E. El-Gamal
National Institute of Oceanography and Fisheries, Kaetbey, Alexandria, Egypt
Received 13 June 2012; accepted 6 August 2012Available online 9 November 2012
*
E
Pe
an
16
ht
KEYWORDS
Oreochromis niloticus;
Monosex production;
17a-Methyltestosterone;
Androgen treatment
Corresponding author.
-mail address: zeinab_elgrei
er review under responsibility
d Fisheries.
Production an
87-4285 ª 2012 National In
tp://dx.doi.org/10.1016/j.ejar
sy@yaho
of Natio
d hostin
stitute of
.2012.08.0
Abstract With the purpose of solving some practical problems concerning the complete masculin-
ization of Oreochromis niloticus by oral administration of 17a-methyltestosterone (17a-MT) with
respect to the dose of the hormone used, different doses of 17a-MT (40, 60 and 80 mg of 17a-MT/kg of feed) were orally administered to sexually undifferentiated fries from the 7th to the
28th day posthatching to produce all male tilapia population.
After 15, 35 and 75 days and 1 year of treatment, growth parameters, survival rate, sex ratio and
gonad histology of the resulting larvae and fish were demonstrated. The results showed that the
highest survival rates of the fry were recorded in the group treated with 60 mg of 17a-MT/kg of feed
compared to the control group, 40 and 80 mg of 17a-MT/kg of feed treated groups. The maximum
sex ratios of males (95% and 97%) were recorded at 60 mg of 17a-MT/kg of diet after 75 days and
one year of treatment respectively.
After the first year, the degree of sex stability was observed significantly shifted towards males.
The histological examination showed that the treatment caused an increase in male gonad recrudes-
cence in most of the treated fish. In presumed genetic females, there are oocytes of young stages,
gonial germ cells and different stages of degenerating oocytes within the period around 35 days
posthatching.
The present results concluded that 17a-MT has a potential effect in directing gonadal sex differ-
entiation of O. niloticus towards males according to the dose involved in the treatment.ª 2012 National Institute of Oceanography and Fisheries. Production and hosting by Elsevier B.V. All
rights reserved.
o.com (Z.A. El-Greisy).
nal Institute of Oceanography
g by Elsevier
Oceanography and Fisheries. Prod
05
Introduction
Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) is likely tobe the most important cultured fish in the 21 century (Ridha,2006). It grows and reproduces in a wide range of environmen-
tal conditions and tolerates stress induced by handling(Tsadik and Bart, 2007). With the purpose of achieving more
uction and hosting by Elsevier B.V. All rights reserved.
60 Z.A. El-Greisy, A.E. El-Gamal
productivity in growing tilapia, Oreochromis niloticus, at theunit time, it is important to produce monosex culture that con-stitutes totally of males (Mair and Little, 1991). Male monosex
tilapia cultures are preferred to females because of the differen-tial growth in favour of males. In males, the metabolic energyis channeled towards growth. They benefit from anabolism
enhancing androgens (Tran-Duy et al., 2008; Angienda et al.,2010). In females, there is a greater reallocation of metabolicenergy towards reproduction.
Although monosex male population can be obtained by di-rect or indirect methods, oral administration of Oreochromisniloticus has been reported to be the most preferred methodin commercial uses (Green and Teichert-coddington, 2000;
Wahby and Shalaby, 2010; Celik et al., 2011). 17a-methyltes-tosterone (17a-MT) is a synthetic male hormone which closelymimics the naturally-produced hormone testosterone. The
most common sex-reversal treatment involves giving a pow-dered fish feed to the first-feeding (and still sexually undifferen-tiated) tilapia fry. This diet contains 30–60 mg 17a-MT/kg of
feed until the 25–60th days posthatching (Macintosh andLittle, 1995). Nile tilapia and the other Oreochromis speciesthat dominate commercial tilapia farming are mouth brooders.
After their eggs are released and fertilized, the female brood-fish carry the eggs orally until they develop into fry (Macintoshand Little, 1995). Treatment with 17a-MT should begin fromthe second or third day after the fry are released from maternal
care. However, other studies recommended the treatment tostart from the seventh day posthatching until 30th day(Nakamura and Iwahashi, 1982).
In the present study, three doses of 17a-MT (40, 60 and 80 mgof 17a-MT/kg of feed) were orally administered to sexuallyundifferentiated fry of Oreochromis niloticus from the 7th to
the 28th dayposthatching to produce allmale tilapia population.The present study aims to investigate the potentiality of dif-
ferent doses of 17a-MT with respect to the determination of the
optimum dose and to demonstrate the degree of sex stability inmonosex Oreochromis niloticus after the first year of treatment.
Materials and methods
Experimental design
Broodfish of Oreochromis niloticus were allowed to breed nat-urally in cement ponds with area of 3 · 6 m, and water heightof 40 cm during June 2011 with a sex ratio of 3 females to
1 male/m3 at El-Serw Station for Fish Researches, NationalInstitute of Oceanography and Fisheries, Egypt. About 400of the newly hatched fry were stocked in a tank (150 L). After
seven days posthatching, when the yolk sacs were absorbed,the fry were divided into four groups in glass aquaria, 50 Leach, with a density of 100 fry for each aquarium. The water
of the aquaria were maintained at pH (7–7.4), dissolvedoxygen (5.5–6.5 mg/l), water temperature was ranged from25 to 28 �C and kept under natural light conditions. After28 days, the fish were transported to the cement ponds until
the 75th day, then transported to the rearing ponds.
Preparing of control and steroid containing diet
A control diet, as described by El-Gamal et al. (2007), con-tained 30% fish meal, 30% solvent-extracted soya bean meal,
18% wheat bran, 13% yellow corn, 6% corn oil, 2% vitaminsand minerals premix and 1% carboxy methyl cellulose.
In addition to the control diet, other three experimental
diets were prepared with the addition of 40, 60 and 80 mg/17a-MT/kg of feed.
They were prepared by the method of spraying the hor-
mone dissolved in 50 ml of 95% ethyl alcohol and mixed wellin fine granules of feed. Glycerin was added at 0.5%/kg by vol-ume to render the harmful effect of the alcohol. The mixture of
feed has been completely dried at room temperature and thensealed in air tight black container and stored in refrigeratorsuntil use to retard bacterial or fungal contamination (Celiket al., 2011).The diets containing 17-aMT were characterized
as follows:
Diet (1): Control (untreated).
Diet (2): control diet + 40 mg of 17a-MT/kg of diet.Diet (3): control diet + 60 mg of 17a-MT/kg of diet.Diet (4): control diet + 80 mg of 17a-MT/kg of diet.
Feeding protocol
The diet of 17a-MT was applied from the 7th to the 28th dayposthatching, after that the feeding of the fish continued on thecontrol diet. The feeding was supplied from two to four timesdaily during the day light hours. At the beginning of feeding,
the diet was given as fine granules. The daily ration of feedranged from 15% to 20% of fish weight until the fry reachesan average length of 15 cm. After that, gradual reduction
down to 10% of fish weight daily until the end of theexperiment.
The mean length, weight and survival rate of the fish in each
treatment were recorded. After one year posthatching, atwhich the fish were completely sexually mature, the percentageof males and females were recorded.
Specifying of sex rates
To find out how sexual development after one year of treat-ment, the sex was determined depending on the secondary sex-
ual characters. In small fish, small pieces of gonads were putbetween two slides and examined under stereo-microscope.
For histological investigation, samples of gonads were col-
lected after 15, 35, 75 days and after one year posthatching.The gonads were fixed in Bouin’s solution for a period of48 h and then transported to 70% alcohol until dehydration
process was completed. Fixation process was followed bydehydration, parafinization and sectioning. After that, the go-nad sections were stained with haematoxilyn and eosin and
then examined under light microscope.
Statistical analysis
In order to calculate the statistical significance between the
growth of the control and those of the groups treated with dif-ferent doses of 17a-MT, a comparison of the different param-eters were described according to Fisher (1950) and Sokal and
Rohlf (1969). T-test was used to find out the statistical signif-icance in terms of growth parameters, survival rates and sexratio.
Monosex production of tilapia, Oreochromis niloticus using different doses of 17a-methyltestosterone 61
Results
Effect of Dietary 17a-methyltestosterone on growth parametersand survival rate of the larvae of Nile tilapia, Oreochromis
niloticus
After 15 days posthatching, the highest values of averageweight (1.97 g) and highest survival rate (93%) of tilapia wererecorded significantly (p < 0.05) in the fry treated with 60 mg
17a-MT/kg diet compared to those of groups treated with 40,80 mg 17a-MT/kg diet or in the untreated control group. Onthe other hand, the lowest values of average weight (0.754 g)and lowest values of survival rate (65%) were recorded in tila-
pia treated with 80 mg 17a-MT/kg diet (p> 0.05) (Table 1).After 35 days posthatching, the highest values of average
weight (3.50 g) and the highest survival rate (94%) of tilapia
were recorded in fry treated with 60 mg 17a-MT /kg diet com-pared to those of fry treated with 40 mg 17a-MT/kg diet,80 mg 17a-MT/kg diet or in the untreated control group. On
the other hand, the lowest values of average weight (2.81 g)
Table 2 Effect of orally-administered 17a-methyltestosterone on gro
35 days of treatment.
Treatment category Growth parameters
Mean length (cm)
Min Max Avg ± SD
Control 3.00 3.80 3.45 ± 0.332
40 mg/kg of diet 4.80 3.90 4.28 ± 0.297
60 mg/kg of diet 5.60 4.30 5.06 ± 0.396
80 mg/kg of diet 4.20 3.30 3.79 ± 0.262
a Significantly different compared to the control group (p < 0.05).
Table 3 Mean weights, survival rates of Oreochromis niloticus reare
of 17a-methyltestosterone.
Treatment category Mean weight (g)
Min Max
Control 12.7 15.8
40 mg/kg of diet 14.9 17.0
60 mg/kg of diet 15.1 18.0
80 mg/kg of diet 13.8 16.5
a Significantly different compared to the control group (p < 0.05).
Table 1 Effect of orally-administered 17a-methyltestosteron on gro
15 days of treatment.
Treatment category Growth parameters
Mean length (cm)
Min Max Avg ± SD
Control 1.20 1.80 1.42 ± 0.200
40 mg/kg of diet 2.70 3.70 2.94 ± 0.377
60 mg/kg of diet 3.50 4.20 3.80 ± 0.221
80 mg/kg of diet 3.10 2.20 2.66 ± 0.341
a Significantly different compared to the control group (p < 0.05).
and lowest values of survival rate (60%) were recorded in tila-pia treated with 80 mg 17a-MT/kg diet as recorded in Table 2.
After 75 days of treatment, the percentages of males were 46,
88, 95 and 65% in control, treated fry with 40, 60 and 80 mg of17a-MT/kg diet respectively. After one year of treatment, thepercentages of males were 30, 85, 97 and 93% in control, treated
fry with 40, 60 and 80 mg of 17a-MT/kg diet respectively(Table 5). It is obvious that methyltestosterone influenced thesex ratio in favour of males. However, the percentage of males
is higher in the treated groups compared to the control.Generally, the highest values of growth parameters and sur-
vival rates of the larvae of Nile tilapia, Oreochromis niloticus,were recorded at the dietary dose of 60 mg of 17a-MT/kg diet
compared to the control, 40 and 80 mg of 17a-MT/kg dietafter 15, 35 and 75 days posthatching (Tables 1–4).
Effect of 17a-methyltestosrerone on sex differentiation of thegonads
Based on histological examination, the ovaries and the
testes of Oreochromis niloticus fry were developed from
wth and survival rate of Nile tilapia, Oreochromis niloticus, after
Survival rate (%)
Mean weight (gm)
Min Max Avg ± SD
1.50 2.00 1.766 ± 0.158 92
2.70 3.30 3.060 ± 0.183 90
3.20 3.90 3.500 ± 0.269a 94
2.50 3.20 2.810 ± 0.199 60
d in cement ponds after 75 days of treatment with different doses
Survival rate (%)
Avg ± SD
14.257 ± 1.018 100
15.871 ± 0.755 100
16.782 ± 0.868a 100
15.040 ± 0.644 70
wth and survival rate of Nile tilapia, Oreochromis niloticus, after
Survival rate (%)
Mean weight (gm)
Min Max Avg ± SD
0.40 0.80 0.500 ± 0.440 88
0.50 1.50 0.975 ± 0.359 79
1.80 2.30 1.970 ± 0.154a 93
0.40 1.30 0.754 ± 0.350 65
62 Z.A. El-Greisy, A.E. El-Gamal
undifferentiated gonadal tissue. The key morphologicalevents are described as follows: (see Table 4).
At 15 days posthatching, the undifferentiated gonads of the
group treated with 40 mg of 17a-MT/kg contained small germ
Figure 1 Histological sections of fry at 15 days posthatching treated w
kg of feed, the gonad appears in pear shaped with gonia and primordia
80 mg of 17a-MT/kg of feed, showing somatic cells (arrow head) and
treated with 60 mg of 17a-methyltestosterone/kg of feed, showing clu
ovarian differentiation in control group at age period from 25 to 31 day
The ovary of treated female with 60 mg of 17a-MT/kg of feed, few oo
400·. (f) Presumptive ovary of treated female with 80 mg of 17a-MT/
Table 4 Mean weight of Oreochromis niloticus in the rearing p
methyltestosterone.
Treatment category Mean weight (g)
Min Max
Control 130 180
40 mg/kg of diet 180 200
60 mg/kg of diet 200 230
80 mg/kg of diet 195 210
a Significantly different compared to the control group (p< 0.05).
cells which were observed under mesonephric duct. The germcells were distinguished easily from the somatic cells by theirdefinite, roundish contour, clear aspect of the cytoplasm and
larger nuclear size of 7–10 lm (Fig. 1a). By that time, no
ith 17a-MT/kg of feed. (a) Gonad treated with 40 mg of 17a-MT/
l germ cells (arrow) (H&E) 100·. (b) Indifferent gonad treated with
primordial germ cells (arrow) (H&E) 400·. (c) Indifferent gonadsters of primordial germ cells after 15 days posthaching. (d) The
s was firstly observed with ovarian cavity (arrow) (H&E) 400·. (e)gonia (arrow head) and large area of stromal cells (arrow) (H&E)
kg of feed (H&E) 400·.
onds after 1 year of treatment with different doses of 17a-
Survival Rate
Avg ± SD
157.50 ± 22.17 100
191.25 ± 8.53 100
215.00 ± 12.90a 100
203.75 ± 7.50 95
Monosex production of tilapia, Oreochromis niloticus using different doses of 17a-methyltestosterone 63
prominent changes were observed in histological aspects andnumber of germ cells of the early gonads. At the same time,the gonads of treated fry with 80 mg of 17a-MT/kg, showed
that they began to shift bilaterally from the dorsal root of mes-entery with small number of somatic cells enclosing primordialgerm cells (Fig. 1b). On the other hand, the gonads of treated
fry with 60 mg of 17a-MT/kg (15 days posthatching), thepaired arrangement of the gonad became more distinctly thanbefore. Active mitotic division of germ cells was seen in most
of the gonads. As a result, germ cells became smaller thanbefore making clusters especially in the anterior region of thegonad (Fig. 1c).
At the period from 25th to 31st day, the first sign of ovarian
differentiation was found. At this period, the gonads fall intotwo groups, the larger gonad contained oogonia with clearovarian cavity and smaller gonad contained cysts of germ cells
as shown in female (Fig. 1d).
Figure 2 Histological sections of fry at age of 21–35 days posthatch
with 40 mg of 17a-MT/kg of feed, showing the ovary contained perin
400·. (b) Presumptive testes treated with 60 mg of 17a-MT/kg of feed,
(H&E) 400·. (c) Presumptive testes treated with 80 mg of 17a-MT/kg
efferent duct appeared towards the outer margin of testes (arrow head
treated with 60 mg of 17a-MT/kg of feed, showing many degenerated o
with 80 mg of 17a-MT/kg of feed, showing many degenerated oocytes
the oocyte appeared in ripe stage (arrow) and few numbers of young
During this period, the ovary of female treated with 60 mgof 17a-MT/kg showed that the ovary contained few oogonia inthe anterior region and a large area of stromal cells that were
dense along the mesentery side (Fig. 1e).The ovary of female treated with 80 mg of 17a-MT/kg
showed that the ovary contained few oogonia and some germ
cells underwent the mitotic division and the ovarian cavity wasclearly observed (Fig. 1f). Ovary of female treated with 40 mgof 17a-MT/kg of feed, contained perinucleolus oocytes filled
up the entire ovary and some ovaries contained lamellae(Fig. 2a). On the other hand, the other type of gonad are foundafter 21–35 days posthatching of treatment with 60 mg of 17a-MT/kg of feed showed that the presumptive testes contained a
large number of germ cells under mitotic division. Further dif-ferentiation or spermatogonial growth was apparent in thepresumptive testes. The testes can be differentiated by having
small slit indicating to the presumptive efferent duct
ing treated with 17a-MT showing: (a) the ovary of female treated
ucleolus oocytes (arrow head) and ovarian cavity (arrow) (H&E)
showing primordial germ cells (arrow) and future of efferent duct
of feed, showing primordial germ cells (arrow) and presumptive
) (H&E) 400·. (d) The ovary of female after 75 days posthatching
ocytes. (e) The ovary of female after 75 days posthatching treated
(H&E) 400·. (f) The ovary of control female after 1 year showing
oocytes (arrow head) (H&E) 100·.
Table 5 Percentage of males and females of Oreochromis
niloticus reared in cement ponds after 75 days and 1 year of
treatment with different doses of 17a-methyltestosterone.
Treatment
category
Sex ratio
After 75 days
of treatment
After 1 year
of treatment
Males
(%)
Females
(%)
Males
(%)
Females
(%)
Control 46 54 30 70
40 mg/kg of diet 88 12 85 15
60 mg/kg of diet 95 5 97 3
80 mg/kg of diet 65 35 93 7
64 Z.A. El-Greisy, A.E. El-Gamal
(Fig. 2b). During the same period, the presumptive testes ofmales after treatment with 80 mg of 17a-MT/kg of feedshowed similar histological features in the testes of fry treated
with 60 mg of 17a-MT/kg of feed. However slow developmentin the testis occurred after treatment with 40 mg of 17a-MT/kgof feed (Fig. 2c).
After 75 days posthatching, the ovary of females treatedwith 60 mg of 17a-MT/kg of feed showed that the large num-ber of young oocytes were deformed and devoid area are free
from oocytes appeared towards the center of the gonad(Fig. 2d). After the ovary treated with 80 mg of 17a-MT/kgof feed at the same period, most of the oocytes were deformedand others were degenerated (Fig. 2e). After one year, the con-
trol female contained the oocytes in advanced stage with fewnumbers of small oocytes (Fig. 2f). During the same period,the testes appeared in mature stage in the group treated with
60 mg of 17a-MT/kg of feed (Fig. 3a). However, after one yearposthatching, the testes contained spermatogenic cells in addi-tion to collected sperms inside the seminiferous tubules
(Fig. 3b).
Figure 3 Histological sections of testes treated with 17a-MT/kg
of feed. (a) After 75 days, the testes of male treated with 60 mg of
17a-MT/kg of feed, showing the testes in mature stage, containing
different spermatogenic cells, sperms aggregated in seminiferous
tubules (arrow) (H&E) 400·. (b) After 1 year, the testes of male
treated with 80 mg of 17a-MT/kg of feed, showing the testes
appeared in spawning stage (arrow) (H&E) 400·.
Sex stability towards all male production
After one year, the mean value of gross weight was higher inthe group of fish previously treated with 60 mg of 17a-MT/kg or 80 mg 17a-MT compared to the other groups. The high-
er value of survival rate was recorded either in control or thetreated doses even 40 mg of 17a-MT (Table 5). The percentageof males was 30, 85, 97 and 93 in control and the groupstreated with 40, 60 and 80 mg of 17a-MT diets respectively.
17a-MT influenced the sex ratio and sex stability of males.However, the percentage of males is higher in the treatedgroups with the hormone compared to the control group.
Discussion
Use of 17a-methyltestosterone hormone to induce sex reversal
in farmed tilapias has become a common practice in manyparts of the world. It is a simple and reliable way to produceall-male tilapia stocks, which consistently grow to a larger uni-
form size than mixed sex or all-female stocks. 17a-Methyltes-tosterone is a synthetically produced anabolic andandrogenic steroid hormone, i.e. it promotes both muscle
growth and the development of male sexual characters. It clo-sely mimics the naturally-produced hormone testosterone(Phelps and Popma, 2000).
A key factor in the success of sex reversal treatments is the
amount of hormone that is actually ingested by each individualfish during its labile period of sexual differentiation. Therefore,in the present study, different concentrations of 17a-MT con-
taining feed were applied so as to observe the effect of thesedifferent doses of 17a-MT during the first 28 days of feedingon sex differentiation.
In the present study, the potentiality of different doses of17a-MT (40, 60 and 80 mg of 17a-MT/kg of feed) was investi-gated and compared to the control group. Monosex tilapiashowed significantly higher weight, length, survival rate com-
pared to the control group (p < 0.05). However, the resultsof our study indicated that certain doses of 17a-MT appearto have a higher anabolic effect on the fry of Oreochromis
niloticus rather than other doses. The higher values of weightof the fish treated with 60 mg of 17a-MT/kg of feed comparedto that of the control, 40, and 80 mg of 17a-MT/kg of diet
after 15, 35 and 75 days of the treatment can be attributedto the anabolic effect of 17a-MT (Jo et al., 1995). In thisrespect, some studies reported that 17a-MT treatment showed
an increase in individual growth of tilapia (Mair et al., 1995;
Monosex production of tilapia, Oreochromis niloticus using different doses of 17a-methyltestosterone 65
Dan and Little, 2000; Little et al., 2003). Other studiesreported that the higher mean weights could be attributed tothe improvement of food conversion efficiency of sex-reversed
fry of Oreochromis niloticus (Chakraborty and Banerjee, 2010).The average of the survival rate increases with the increase
of age of the larvae. However, some studies reported that 17a-methyltestosterone treatment has no effect on survival of tila-pia (Vera Cruz and Mair, 1994; Chakraborty et al., 2011). Thesex ratio also showed an increase in the group treated with
17a-MT. After 75 days of treatment, the percentage of malesincreased to reach the maximum value (95%) at 60 mg of17a-methyltestosterone/kg of feed. After one year, the percent-age of males increased to reach the maximum value (97%) at
the same dose.It has been reported by Barry et al. (2007) and Green and
Teichert-Coddington (2000), that over 95% of the population
was masculinized in 21–28 days when 30-60 mg 17a-MT/kgfeed with 17a-MT that was applied orally to the tilapia larvae(7–12 days of age, 9–11 mm TL and 10–15 mg of total weight).
In the present study as well, the highest sex reversal occurred at60 mg/kg feed dose.
Methyltestosterone suppressed the oogenesis. This inhibi-
tory effect on the development of oocytes is dependent on thedose of methyltestosterone. The ovary is almost occupied by so-matic elements (Wolf et al., 2004). It is important to considerthe dose of the hormone to avoid the problems related to over-
doses. Goudie et al. (1983) reported that excessive doses of hor-mone lead to sterility or paradoxical feminization followingaromatization of androgens to estrogens, although sub-optimal
treatments resulted in intersexes (Popma and Green, 1990).In the present study, even though the administration of
17a-MT was commenced prior to the stage of ovarian differen-
tiation, it could not completely prevent the presumed geneti-cally females to produce at least young ooytes at the earlystages of maturation.
Generally, methyltestosterone influenced the sex ratio in fa-vour of males. Independent on the dose, the percentage ofmales is higher in the treated groups.
Depending on histological observations in the present
study, the first sign of gonadal development is the formationof genital ridge and appearance of primordial germ cells(PGC). They were located between the gut and kidney. Similar
observations were recorded by Nakamura (1984) on two spe-cies of salmonids.
As described previously, the initial ovaries either in control
or in treated groups were easily identified by their well devel-oped perinucleolus oocytes, whereas the testes did not showa clear distinction from undifferentiated gonads. Similar obser-vations were noticed by Sacobie and Benfey (2005).
As described in Tilapia mossambica, treated with methyltes-tosterone at dose of 50 lg/g of diet, some germ cells in the go-nads of possible genetic females underwent oogenesis even
under the influence of androgen, but were found to be degen-erated eventually (Nakamura et al., 1974). High doses of 17a-MT did not release milt in Grouper, Epinephelus suillus. It
caused malformation or even agenesis of the sperm duct sys-tem (Tan-Fermin et al., 1994).
In this respect, long-term administration of high dosages of
methyltestosterone has also been reported to inhibit spermia-tion in immature gonochoristic milk fish (Lee et al., 1986).
In conclusion, the present study establishes base line regard-ing the best dosage of 17a-MT (60 mg/kg of 17a-MT) on sex
reversal of Oreochromis niloticus fry. It revealed that the highervalues of mean length, weight and survival rates were recordedin fish treated with 60 mg of 17a-MT/kg of feed. Further re-
searches on histological and morphological characteristics ofgerm cells of the gonad at that critical period of gonadal devel-opment must be studied to throw the light on how mechanism
of hormone induced sex reversal in fish. Other factors ratherthan the dose of the hormone could be investigated in combina-tion with the hormone dose to increase the percentage of male
produced.
References
Angienda, P.O., Aketch, B.O., Waindi, E.N., 2010. Development of
all-male fingerlings by heat treatment and the genetic mechanism of
heat induced sex determination in Nile tilapia (Oreochromis
niloticus L.). International Journal of Biological and Life Sciences
6 (1), 38–43.
Barry, T.P., Marwah, A., Marwah, P., 2007. Stability of 17a-methyl
testosterone in fish feed. Aquaculture 271, 523–529.
Celik, I., Guner, Y., Celik, P., 2011. Effect of orally-administered 17a-methyltestosterone at different doses on the sex reversal of the Nile
tilapia (Oreochromis niloticus, Linneaus 1758). Journal of Animal
and Veterinary Advances 10 (7), 853–857.
Chakraborty, S.B., Banerjee, S., 2010. Comparative growth perfor-
mance of mixed-sex and monosex Nile tilapia population in
freshwater cage culture system under Indian perspective. Interna-
tional Journal of Biology 2 (1), 44–50.
Chakraborty, S.B., Mazumdar, D., Chatterji, U., Banerjee, S., 2011.
Growth of mixed sex and monosex Nile tilapia in different culture
systems. Turkish Journal of Fisheries and Aquatic Science 11, 131–
138.
Dan, N.C., Little, D.C., 2000. The culture performance of monosex
and mixed-sex new-season and overwintered fry in three strains of
Nile tilapia (Oreochromis niloticus) in northern Vietnam. Aquacul-
ture 10 (2), 32–34.
El-Gamal, A.E., El-Greisy, Z.A., El-Ebiary, E.H., 2007. Synergistic
effects of vitamins C & E, and selenium on the reproductive
performance of Nile tilapia, Oreochromis niloticus. Journal of
Applied Sciences Research 3 (7), 564–573.
Fisher, R.A., 1950. Statistical Methods for Research, Workers, 11th
ed. Oliver and Boyd, London.
Goudie, C.A., Redner, B.D., Simco, B.A., Davis, K.B., 1983.
Feminization of channel catfish by oral administration of steroid
sex hormones. Transactions of the American Fisheries Society 112,
670–672.
Green, B.W., Teichert-Coddington, D.R., 2000. Human food safety
and environmental assessment of the use of 17a-methyltestosterone
to produce male tilapia in the United States. Journal of World
Aquaculture Society 31, 337–357.
Jo, J.-Y., Smitherman, R.O., Tave, D., 1995. Effect of six levels of
dietary 17a-methyltestosterone on sex-reversal and growth of
Oreochromis aureus (Steindachner) and Oreochromis niloticus
(Linnaeus). Journal of Aquaculture 8 (2), 77–83.
Lee, C.S., Weber, G.M., Tamaru, C.S., 1986. Effect of orally-
administered 17a-methyltestosterone on spermatogenesis in imma-
ture milkfish Chanos chanos Forsskal. Journal of Fish Biology 29,
567–572.
Little, D.C., Bhujel, R.C., Pham, T.A., 2003. Advanced nursing of
mixed-sex and mono-sex tilapia (Oreochromis niloticus) fry, and its
impact on subsequent growth in fertilized ponds. Aquaculture 221,
265–276.
Macintosh, D.J., Little, D.C., 1995. Nile tilapia (Oreochromis niloti-
cus). In: Bromage, N.R., Roberts, R.J. (Eds.), Broodstock Man-
agement and Egg and Larval Quality. Blackwell Scientific Ltd.,
USA, pp. 277–320 (Chapter 12).
66 Z.A. El-Greisy, A.E. El-Gamal
Mair, G.C., Little, D.C., 1991. Population control in farmed tilapias.
NAGA – The ICLARM Quarterly 14, 8–13.
Mair, G.C., Abucay, J.S., Beardmore, J.A., Skibinski, D.O.F., 1995.
Growth performance trials of genetically male tilapia (G17a-MT)
derived from YY-males in Oreochromis niloticus L.: On station
compositions with mixed sex and sex reversed male populations.
Aquaculture 137, 313–322.
Nakamura, M., 1984. Effects of estradiol-17b on gonadal sex
differentiation in two species of salmonids, the masu salmon,
Oncorhynchus masou, and the chum salmon O. keta. Aquaculture
43, 83–90.
Nakamura, M., Iwahashi, M., 1982. Studies on the practical mascu-
linization in Tilapia nilotica by the oral administration of androgen.
Bulletin of the Japanese Society of Scientific Fisheries 48 (6), 763–
769.
Nakamura, M., Takahashi, H., Hiroi, O., 1974. Sex differentiation of
the gonad in the masu salmon (Oncorhynchus masou). Scientific
Reports of the Hokkaido Salmon Hatchery 28, 1–8.
Popma, T.J., Green, B.W., 1990. Sex reversal of tilapia in earthen
ponds. Research and Development Series. International Center for
Aquaculture, Alabama Agriculture Experiment Station, Auburn
University, Auburn, AL, p. 15.
Phelps, R.P., Popma, T.J., 2000. Sex reversal of tilapia. In: Costa-
Pierce, B.A., Rakocy, J.E. (Eds.), . In: Tilapia Aquaculture in the
Americas, vol. 2. The World Aquaculture Society, Baton Rouge,
LA, United States, pp. 34–59.
Ridha, M.T., 2006. Comparative study of growth performance of three
strains of Nile tilapia, Oreochromis niloticus, L. at two stocking
densities. Aquaculture Research 37, 172–179.
Sacobie, C.F.D., Benfey, T.J., 2005. Sex differentiation and early
gonadal development in brook trout. North American Journal of
Aquaculture 67, 181–186.
Sokal, R.R., Rohlf, F.J., 1969. Biometry. Freeman and Company, San
Francisco, pp. 776.
Tan-Fermin, J.D., Garcia, L.M.B., Castillo, A.R., 1994. Induction of
sex inversion in Juvenile Grouper, Epinephelus suillus, (Valenci-
ennes) by injections of 17a-methyltestosterone. Japanese Journal of
Ichthyology 40 (4), 413–420.
Tran-Duy, A., Schrama, J.W., van Dam, A.A., Verreth, J.A.J., 2008.
Effects of oxygen concentration and body weight on maximum feed
intake, growth and hematological parameters of Nile tilapia,
Oreochromis niloticus. Aquaculture 275, 152–162.
Tsadik, G.G., Bart, A.N., 2007. Effect of feeding stocking density and
water-flow rate on fecundity, spawning frequency and egg quality
of Nile tilapia, Oreochromis niloticus (L.). Aquaculture 272, 380–
388.
Vera Cruz, E.M., Mair, G.C., 1994. Conditions for effective androgen
sex reversal in Oreochromis niloticus (L.). Aquaculture 122, 237–
248.
Wahby, O.M., Shalaby, S.H., 2010. Oral administration of testoster-
one in fish diet affect sex differentiation and testis development in
tilapia. Research Journal of Agriculture and Biological Sciences 6
(6), 946–952.
Wolf, C.J., Gerald, A.L., Earl, L., Gray, J.R., 2004. Interactive effects
of vinclozolin & testosterone propionate on sexual differentiation
of the rats. Toxicological Sciences 78, 135–143.