Abstract
Some aspects of reproductive biology and fry rearing of freshwater mud eel
(Monopterus cuchia) and freshwater spiny eel (Mastacembelus armatus) of
Mymensingh region have been investigated during September 2003 to February 2006
in the Department of Aquaculture, Bangladesh Agricultural University (BAU),
Mymensingh. It was found that both the eels could be sexed on the basis of vent size
with colour, abdomen shape and body colour during the breeding period. Out of
breeding season it could be sexed by examining the gonads. The mean (± S.E) GSI
values showed breeding period from March to April with a peak in April (0.82 ± 0.04,
in male and 6.02 ± 0.65, in female) for the mud eel whereas the mean (± S.E) GSI
values showed breeding period from March to July with a peak in March (0.84 ± 0.07,
in male and 6.23 ± 0.75, in female) for the spiny eel. The maximum mean (± S.E) ova
diameter was (3.40 ± 0.11 mm) for the mud eel and was (2.04 ± 0.06 mm) for the
spiny eel. The ripe ova of both the species were to be spherical and uniform in
diameter which indicated that the eggs were shed in a single batch during the
spawning. The fecundity of the mud eel varied from 397 to 3527 for the eel ranging
from 520 mm to 810 mm and the fecundity of the spiny eel varied from 3155 to
24684 for the eel ranging from 260 mm to 535 mm. The fecundity increased with the
increase in length and weight of both the eels. The logarithmic relationship of the
fecundity and body weight, Log F = 4.116 + 0.541 x Log BW and Log F = 2.050 +
0.772 x Log BW were found to be more correlated than the other variables for the
eels. From the gonadal histology of both the eels, it was observed that six different
types of oocytes in the prepared slides of mud eel were as oogonia, chromatin nuclear
stage, early perinuclear stage, late perinuclear stage, yolk vesicle stage and yolk
granule stage oocyte whereas seven different types of oocyte were found in the
prepared slides of spiny eel as late yolk granule stage oocyte and the above six
oocytes of mud eel. The cyclic gonad histological studies of mud eel confirmed the
breeding period during March to April with a peak in April whereas the cyclic gonad
histological studies of spiny eel confirmed the breeding period during the March to
July with a peak in March. The mud eel spawned in an artificially created
environment in the cemented cistern contained mud and water hyacinth as shelter at
water temperature 27 to 30°C during early June. It was observed that the parents
combinely took parental care to their eggs and offsprings up to their independent
movement that was taking time, 7-10 days and during that period offspring achieved
around 50 mm length. From the investigation it was observed that the hatching period
was around 12 to 15 days. However, the spiny eel did not respond in an artificially
created environment. Induced breeding of mud eel and spiny eel by various doses (10,
20, 30, 40 and 50 mg/kg body weight) did not respond. On the other hand fish died
with higher doses (40 and 50 mg/kg body weight). From the histological study it was
clearly found that the low doses of carp pituitary extract (CPE) in weekly intervals
also fail to enhance the gonadal development of both mud eel and spiny eel. The
lobule disruption rate increased with the increasing dose of pituitary extract for both
the eels. It was found that the chopped small fish and the chopped prawn were the
best foods in respect of growth and survival rate for mud eel and spiny eel
respectively. It was found that the water hyacinth was the best shelter in respect of
growth and survival rate for both mud eel and spiny eel.