Environmental factors
affecting embryonic development, hatching and survival of early stages of
grouper Epinephelus coioides
(a study conducted by SEAFDEC Aquaculture
Department)
The effects of some environmental factors on
embryonic development, hatching and survival of early larval stages of
grouper were examined. Spontaneously spawned grouper eggs in tanks were
collected and stocked in 3-1 containers at a density of 400 eggs/1 (best
density determined in previous experiment). Four aeration levels were
tested: T1 - no aeration, T2 - 100 ml/min, T3 - 500 ml/min, and T4 - 1,000
ml/ min. Embryonic survival was significantly higher in T2 (51.0%) than in
T1 and T3 (40-8%). Lowest survival was observed in T4 (30.1%). Hatching rate
was highest in T2 (97.3%) but was not markedly different from T3 (86.4%).
Hatching rate in T4 (78.3%) was lower than T2 but was not significantly
different from T3. Lowest hatching was observed in T1 (43.7%). The
percentage of abnormal newly hatched larvae was highest in T4 (41.4%),
followed by T3 (31.6%), and T1 (16.0%). T2 had the lowest abnormal newly
hatched larvae (6.7%).
Grouper eggs at early cleavage stage abruptly exposed
to salinities of 8, 16, 24, 32, and 40 ppt had a significantly higher
embryonic survival at 32 and 40 ppt (52.8-54.4%). Hatching rate was also
significantly higher in 32 and 40 ppt when abrupt transfer was made at early
cleavage (69.9-78.3%) than at the "eyed" stage (40.5-55.8%).
Hatching was low in 8-24 ppt regardless of embryonic stage tested (0-29%).
A similar trend was observed for the percentage of normal newly hatched
larvae. In contrast, newly hatched larvae abruptly transferred to test
salinities between 8-40 ppt showed a consistently higher survival at 16 ppt
until 5 days. Embryonic development of eggs was influenced by the
interaction of salinity and temperature. At the cleavage stage, the rates of
embryonic development and hatching were generally higher at 28°C
but were highest in 32 ppt regardless of test temperatures (25-32°C).
At the eyed stage, hatching rate increased with increasing salinity until 32
ppt, at 26.5-32°C. The percentage of abnormal and moribund
larvae was higher at 16 ppt regardless of incubation temperature and stage
of embryonic development. Newly hatched larvae abruptly transferred to
various test temperature and salinity survived better until Day 5 at 16-24
ppt. Highest survival was observed at 16 ppt and 25°C. Initial results
indicate relatively larger larvae with bigger yolk and oil globule compared
to larvae at higher temperature and salinity. At the onset of feeding,
feeding incidence was higher in low aeration levels (50ml/min) than in
moderate (100 ml/min) and in high (250 ml/min). Without aeration, all
newly-hatched larvae died a day after stocking. Only larvae stocked in low
aeration level survived 6 days post hatching.
On the effects of illumination on first feeding
larvae, preliminary data suggest that a light intensity of about 200 lux is
required to initiate successful feeding.
(from Grouper Research Briefs in Aquaculture Asia,
Vol. VI, No. 2, April-June 2001)