Biological characterization of wild cobia, Rachycentron canadum (linnaeus, 1766) off Dungun coast, Terengganu, Malaysia for stock management and aquaculture
Investigation of some aspects of biology of a recreationally and commercially important fish, cobia, Rachycentron canadum in Dungun coast, Malaysia was conducted between April 2014 and May 2015. A total of 249 specimens were opportunistically collected from the catches of trawl net, gill net a...
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| Format: | Thesis |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/68671/1/fp%202016%2029%20ir.pdf |
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| Summary: | Investigation of some aspects of biology of a recreationally and commercially
important fish, cobia, Rachycentron canadum in Dungun coast, Malaysia was
conducted between April 2014 and May 2015. A total of 249 specimens were
opportunistically collected from the catches of trawl net, gill net and by hooks and
line. The total length ranged from 39.20 to 143.00 cm (88.29 ± 1.28 cm), fork length
ranged from 37.50 to 124.00 cm (78.69 ± 1.09 cm) while the wet weight ranged from
0.50 to 20.40 kg (5.51 ± 0.26 kg). There was no significant difference in all the
morphometric characters between sexes except for head width (HW) (p < 0.05). Ten
(10) out of the seventeen (17) truss distances in the body landmarks of cobia showed
significant differences between males and females. The equation of length-weight
(LW) relationship for combined sex was W = 0.000002FL3.3204 (R² = 0.92). The
growth of cobia in Dungun water followed positive allometric as the growth
coefficient (b) was higher than 3. Observed length frequency of both sex followed a
normal distribution pattern and there was a predominance of cobia in the medium
size range from 65 - 85 cm fork length for the females and 55 - 90 cm for the males.
The sex ratio of females to males was 1:1.18 and it was not significantly different
from the expected 1:1 (X2 = 2.12 df = 1; p < 0.05). Growth parameters of von
Bertalanffy growth formula for cobia estimated were L = 142.00 cm, K = 1.20 yr-1,
while natural mortality rates (M), fishing mortality rate (F), total mortality (Z) and
Exploitation rate (E) estimated were 1.34, 0.95, 2.29 and 0.41 respectively. The
maximum allowable limit of exploitation (Emax) was estimated to be 0.56. The sizes
attained by cobia at the end of age 1 (year) was 99.28 cm. The estimation of fork
length at first maturity (Lmat) from the plot of gonadosomatic index (GSI) against
fork length (FL) indicated early maturation of males compared to females with
respective value of 70 cm and 72 cm. Males with mature gonads were encountered
throughout the year, while the proportion of mature females was higher in March and
November, and this may be taken as the peak of the spawning period, even though females with hydrated oocyte were also obtained in April, May, June, July and
September. The mean batch fecundity (BF) for all matured females with hydrated
oocytes was ranged from 54886 to 4316648, (11,37,317 ± 183712) while average
eggs per gram of ovary were ranged from 2108 to 5413 (3427.032 ± 128.73) . Weak
positive correlation (r2 = 0.48) was found between the BF and female fork length
with equation BF = 38732.03FL-2200000. Similarly, BF was significantly correlated
with ovary-free body weight (r2 = 0.56). Histological data support continuous
spawning characteristics of cobia as oocyte size frequency distribution showed
progressive batch development. Increase in GSI was observed from September to
November and it reached the peak in March which corresponds to the period when
the highest proportion of matured females was caught. Study on the stomach content
of the cobia, R. canadum in Dungun coast, showed that the bony fish was the
dominant group in the diet with crustacean and mollusc contributing less. The
percentage index of relative important (% IRI) values of fish, crustacean and mollusc
were 72.27%, 2.98% and 24.75% respectively. Out of the 231 cobia specimens
examined in this study, 111 were found to contain food in their stomach, out of
which 98 had at least one identifiable prey items. Gut content analysis revealed that
fish was consumed by cobia all the year round with Hilsa sp., Alepes sp. and
Carangides sp. being the frequently encountered species. Higher stomach fullness
index (SFI) was recorded in the month of April, June and November with values of
2.88, 2.06 and 2.42 respectively while lower SFI was in the month of May and
August with values of 0.67 and 0.86 respectively. The percentage of empty
coefficient (EC) was higher in October, August and July with values of 80%, 70%
and 69% respectively, intermediate in the remaining month as values were about
50%. This stomach fullness index SFI and EC suggest moderate feeding intensity of
cobia in the waters of Dungun. The proximate and chemical composition of cobia
species from Dungun and its seasonal changes was examined. The result showed that
lipids content was significantly (p < 0.05) higher in females (6.38 ± 0.19) than males
(5.44 ± 0.11). No significant (p < 0.05) difference was found in the moisture, ash,
total cholesterol and malondialdehyde (MDA) based on season, sex and feeding
regime. In the fatty acid (FA) composition of the muscle tissue, the unsaturated class
was dominant followed by saturated FA followed by the monoenes. Similar trend
was found in the liver. Total n-3 poly-unsaturated fatty acid (PUFA) was higher
compared to the total PUFA (n-6) in the muscle, and the total PUFA (n-6) was
significantly (p < 0.05) higher in the muscle during the monsoon. Other FA classes
that showed significant (p < 0.05) seasonal differences in the muscle were
pentadecanoic acid, palmitoleic acid and linoleic acid. However, in the liver, the total
saturated, total monones, total PUFA (n-6) and total PUFA (n-3) showed significant
(p < 0.05) seasonal variation. The FA composition of males and females cobia did
not show significant (p < 0.05) differences. During starvation in cobia, a significant
reduction in total PUFA n-6, pentadeconoic acid, and palmitoleic acid was observed
in the muscle. The result of this work suggests adult cobia in Malaysia preferred
bony fishes as food while it reproductive period was continuous and cobia lipid
profiles contained appreciable quantity of PUFA such as docosahexaenoic,
eicosapentaenoic and arachidonic acids and it can be promoted for human
consumption. |
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