Page 37 - World Aquaculture Magazine - March 2011

World Aquaculture 35
Table 1. Cobia spawning and hatching performance at ACAAB during
the 2008 and 2009 trials.
Year 2008
No. Spawning Salinity Av. water No. eggs Incub. Hatching
Broodstock period (days) (‰) temp. (ºC) incub.(103) period (hrs) rate (%)
39♀:39♂ 38 51 26 7461.89 34 37.10
3♀:3♂ 7 37 26 865.20 34 65.85
Year 2009
15♀:30♂ 48 37 26.4 12699.05 36 69.98
entaenoic acid, >30 percent docosa-
heexaenoic acid [DHA], >2.0 percent
arachidonic acid prior to feeding) were
offered. Rotifers were added twice dai-
ly to maintain a density of 10-15 indi-
viduals/ml in the LRTs. During rotifer
feeding water exchange was done only
during night at a rate of 30-50 percent
of volume.
From days 8 to 25 ph, enriched Ar-
temia nauplii were added to the LRTs
at 0.5-1 nauplius/ml. Additionally,
copepod nauplii collected from the
shrimp ponds were provided to the lar-
vae from days 10 to 25 ph at a rate of
≤1 individual/ml. The addition of arti-
ficial feed (Love larva3) started on day
15 ph with the small feed size of 198
µm (57.40 percent crude protein, 12.42
percent fat) until day 25 ph. From days
20 to 35 ph, artificial feed of medium
size 308-476 µm (crude protein 58.35
percent, 13.94 percent fat) was added
and, from days 30 to 40 ph, the larger
size artificial feed, 680-1058 µm (crude
protein 56.23 percent, 3.52 percent fat)
was provided (Figure 3).
No newly hatched larvae reared in
51 ppt seawater during 2008 fed and all
died on day 3 ph. It was reported that
in Taiwan, cobia food uptake was re-
duced by 50 percent when salinity was
increased from 35 ppt to 43 ppt and
when it was increased to 47 ppt, food
uptake virtually stopped and mortality
began (ACE 2003).
Larvae reared at 37 ppt in 2008
yielded 8,000 fully metamorphosed
8.60 cm total length, 1.82 g fingerlings
by day 40 ph for an overall survival
rate of 1.03 percent. The 2009 trials,
where fish were spawned, hatched and
reared 37 ppt, generated a total of
48,428 fingerlings averaging 7.40 cm in
length and 1.90 g BW (Figure 4)/ The
average survival rate attained was 0.54
percent.
Cannibalism was believed to be the
major cause of mortality during the
later stages of larval rearing from day
20 ph. To reduce cannibalism and size
variability cobia were graded daily by
size after day 20 and large individu-
als were separated out and stocked in
different LRTs (Figure 5). It was also
believed that the quantity of copepods
provided to the larvae (≤1 individual/
mL) was not sufficient to maintain
Fig. 3. Feeding schedule for larval cobia rearing.
Fig. 4. Forty-day weaned cobia.
Table 2. Larval rearing of Cobia at ACAAB during the 2008 and 2009
trials.
Year 2008
Salinity No. larvae Rearing Av.water No. Survival
(‰) stocked (106) period (days) temp. (ºC) fingerlings rate (%)
51 1.99 40 25 0.0 0.0
37 0.78 40 25 8000 1.03
Year 2009
37 9.74 37 27 45000 0.54