Abstract:
Orange mud crab, Scylla olivacea (Herbst, 1796) is an important fishery products in
Malaysia. Age study is important to generate the information on growth, recruitment,
longevity, mortality for mud crab stock assessment. The aim of this study is to investigate
the Growth Band Counts (GBC) deposited in thin sections of gastric mill of S. olivacea
as age indicator for this species. A total of 90 wild caught S. olivacea were sampled from
Setiu Wetlands, Peninsular Malaysia (February – October 2016) and 25 individuals of S.
olivacea were reared in the hatchery of Institute of Tropical Aquaculture, Universiti
Malaysia Terengganu for one year (March 2016 - March 2017). The periodicity of GBC
in gastric mill of S. olivacea was validated using reared of known age samples. The results
revealed that the presence of one GBC in reared S. olivacea were parallel to the age one
year old of S. olivacea absolute age. One to three GBC were present in wild caught S. olivacea which indicated the age of one to three years old, respectively. There was a
significantly positive relationship between Carapace Width (CW) and age, as the number
of growth bands increased with putative age. The accuracy of bands counting was
assessed by lower coefficient of variation values of reared and wild caught S. olivacea
with 6.00 – 6.23% and 8.52 – 8.40%, respectively. Using the von Bertalanffy Growth
Model equation, the growth parameters of S. olivacea was estimated and growth curves
was fitted to CW at age data. The growth parameters such as asymptotic CW (CW∞),
growth coefficient (K year
-1
) and initial condition parameter (t0) of the known age S.
olivacea were narrower at 20.07 cm, 0.31 year
-1
and - 0.20 than the wild samples at 28.01
cm, 0.36 year
-1
and - 0.73 for female and at 29.34 cm, 0.38 year
-1
and - 0.79 for male,
respectively. The age composition suggested that S. olivacea population found in the Setiu
Wetlands, Peninsular Malaysia has at least reached the age of 2 years old. The findings
obtained from this study would substantially improve the direct age - based assessment
for biological and ecological studies of mud crabs.
