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induced spawing by affaqahmedkhan


									Material and Methods

The experiments were conducted in fish farms in three southern states of India, viz.
Karnataka, Andhra Pradesh and Tamil Nadu. Mature male and female carp were selected
based on external secondary sexual characters (Jhingran and Pullin 1984). In the case of
rohu and mrigal, varying doses of Ovaprim (0.2-0.5 ml/kg) were tried, while in catla only
one dose (0.5 ml/kg) was tried due partly to insufficient number of brood fish. Females of
all the three species were injected intramuscularly with Ovaprim in a single dose, while
males were given carp pituitary extract at 3-4 mg/kg, 6 hr after injecting females. The
males were released with the injected females only after hormone administration, which
was adjusted to fall between 17 and 20 hr. Control fish were injected carp pituitary
extract in two doses for females (4 and 8 mg/kg) at an interval of 6 hr and a single dose
for males (3-4 mg/kg) at the time of second injection to females. On a few occasions, fish
treated with a single dose of Ovaprim solvent (0.5 ml/kg for females and 0.15 ml/kg for
males) were used as control. In some of the trials carried out in July with robe, both
female and male fish were injected Ovaprim simultaneously at 0.4 and 0.15 ml/kg,
respectively. However, in August, higher dosages (0.6 and 1.2 ml/kg for female and 0.2
ml/kg for male) were also tried, since it has been reported that the carp pituitary dose
required for induced breeding is higher when the water temperature goes beyond 30 C
(Rao and Gnaneshwar 1988). For the August trials, female fish receiving either split dose
or a single dose (total of 18 mg/kg) and males getting only a single dose (6 mg/kg) of
pituitary extract served as control. The Ovaprim used in our study had 20/ug of an
analogue of salmon gonadotropin releasing hormone (sGnRH) (D-Arg6, Trp7, Leu8, Pro9
NEt)-LH-RH and 10 mg domperidone, a dopamine antagonist, per ml.

The breeding tests were conducted by pairing each female with two males in a cloth hapa
measuring 2.5 x 1.2 x 1 m, fixed in ponds provided with moderate circulation of water.
All the trials in Tamil Hadu and a few trials in Andhra Pradesh with rohu were conducted
in Chinese hatcheries of 4.2 m diameter and 1.2 m height. These hatcheries are not the
breeding pools, but the hatching pools which are commonly used for breeding by keeping
the fish in the outer chamber. Fish were examined for the breeding response usually 10 hr
after the first injection and subsequently at hourly intervals. The percentage of
fertilization was calculated using samples of eggs developed for a minimum period of 4-6
hr. Before releasing the spawned females, they were examined for the extent of
spawning. Whenever a large number of eggs oozed out freely by applying slight pressure
on the abdomen, they were classified as partially spawned. In cases where no natural
spawning had taken place, if the eggs were oozing out with slight pressure on the
abdomen, they were classified as ovulated.

In most of the experiments, eggs from the same species were grouped together and
hatched in the Chinese hatcheries. However, in Karnataka, catla eggs were hatched in
traditional cloth hapas (2 x 1 x 1 m).

The general weather that prevailed during the month of July in [arnataka and Andhra
Pradesh was conducive for breeding of carps. Though the temperature was relatively
higher in Andhra Pradesh (27.529°C) as compared with [arnataka (2324.5.C), there were
light showers in both the states on almost all days during the experiments. However,
temperatures recorded during the experiments conducted in Andhra Pradesh in August
(31-32.5-C) and in Tamil Nadu in September (30-30.5.C) were not very favorable for
breeding of carps, especially because of little rainfall.

Results of the experiments on mrigal are presented in Table 1. A total of 21 females were
treated with different doses of Ovaprim, nine were administered a uniform dosage of 12
mg/kg carp pituitary extract, and three were given Ovaprim solvent, the latter two being
control groups. Of the seven females treated with Ovaprim at 0.5 ml/kg, five spawned,
while one got plugged and in another, spawning was partial. All the six females injected
wit 0.4 ml/kg spawned naturally. Among the 4 females treated with 0.3 ml/kg, three
spawned naturally and the fourth one showed only ovulation. Out of the four females
injected with 0.2 ml/kg, only one spawned, while none of those treated with Ovaprim
solvent responded. Except for one fish which spawned partially and another that did not
spawn, all the others treated with pituitary extract bred naturally. The percentage of
fertilization was usually high in Ovaprim treated fish (74-99:) as compared with pituitary
extract injected fish (11-97%).

All the seven females of catla treated with Ovaprim at 0.5 ml/kg responded well, though
the spawning was partial in one fish and fertilization rate varied from 60 to 87Z (Table
1). The two females injected with Ovaprim solvent did not respond. Since in one instance
most of the eggs went out of the breeding hapa through a hole, the number of eggs
released could not be ascertained.

Table 2 summarizes the results of the experiments with rohu. All the three females
treated with carp pituitary spawned, though spawning was partial in one instance with
low fertilization percentage (43%). Out of the 16 females administered with 0.5 ml/kg
Ovaprim, 15 females spawned, whereas one female did not respond. However, spawning
was partial in two females and fertilization was poor (3 and 31%). All the 29 females
treated with 0.4 ml/kg responded positively. At 0.3 ml/kg, no female spawned naturally,
but all ovulated. Out of the three females treated with 0.25 ml/kg, none spawned but
ovulation was recorded in one. Both the groups treated with 0.2 ml/kg Ovaprim and
Ovaprim solvent did not respond.

The results of experiments pertaining to single and simultaneous administration of
Ovaprim to both sexes of rohu are given in Table 3. Out of the 19 sets treated at 0.4
ml/kg for female and 0.15 ml/kg for male, 14 sets responded positively with high
fertilization (76 - 94%). Even in the experiments conducted during August, fish injected
with 0.4 ml/kg also spawned like those injected with 0.6 and 1.2 ml/kg, the latter doses
were tried to confirm the need for higher doses of inducing agents at higher temperatures.
None of the fish treated with pituitary extract (18 mg/kg for female and 6 mg/kg for
male) in a single dose responded. However, those fish given pituitary in two doses
responded positively (Table 3). The number of eggs obtained, spawning rate and
fertilization were poor in most of the trials conducted during August

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