Ordonio-Aguilar, R.S., Kohno, H., Ohno, A., Moteki, M., Taki, Y.
Abstract:
The grouper, Epinephelus, coioides (E. suillus, syn.) is one of the
more important species for aquaculture in Southeast Asia. Therefore,
its biology has been well studied and its propagation properly
documented. However, the rearing of this species is still considered
difficult owing to low survival results during the early stages. In this
study, characters related to the transition from endogenous nutrition
to exogenous feeding were studied to account for such low survival
during this critical phase.
Larvae used in this study originated from eggs naturally spawned at
the Southeast Asian Fisheries Development Center
(SEAFDEC-AQD). Hatching rates varied from 6.9-14.7% (mean
9.77%). Newly-hatched larvae were placed in 500-l tanks at a density
of 30 ind/l and fed with rotifers and green algae. Samples of 10-20
larvae were collected daily and data on total length, yolk volume, oil
globule diameter, eye pigmentation and mouth width were recorded.
The number of rotifers in the digestive tract was examined at 67, 69.5,
98 and 118 hours after hatching (HAH). Mortality patterns of unfed
larvae were examined in 2-l beakers.
The larvae grew rapidly during the first 40 HAH and levelled off. The
survival rate of unfed larvae decreased to 80% at 25 HAH, 17% at 68
HAH and all larvae at 111 HAH. Newly-hatched larvae had a mean
yolk volume of 1354/10^4 mm^3 and an oil globule of 33.9/10^4
mm^3. The yolk was consumed rapidly after hatching and was
completely gone by 91 HAM.. On the other hand, the oil globule was
consumed more slowly till 54.5 HAH, after which it was rapidly used
up till completely resorbed at 98 HAH. Eye pigmentation was
complete by 54.5 HAH and opening of the mouth was observed.
Exogenous feeding on rotifers started at 69.5 HAH.
Comparing this larvae to other previously-studied species, the grouper
was last to initially open its mouth. Its food reserve at mouth opening
and onset of feeding was smallest among those compared. The time
from the onset of feeding to the exhaustion of exogenous nutrition
was shortest. Based on these, the larvae were most disadvantaged
during the mixed feeding stage. These factors seem to account for the
difficulty in rearing the grouper larvae. In spite of the above reasons
however, the larvae has a wide mouth and large body and feeding it a
more suitable food organism, other than rotifer, may help the larvae
to overcome this period.
(College of Fisheries, University of the Philippines in the Visayas,
Miagao, Iloilo, Philippines 5023)