Abstract:
Population studies on blue swimming crab, Portunus pelagicus are needed
to provide exploitation rate and, other biological and fisheries information.
Lipofuscin (LF) levels in eyestalks of P. pelagicus, were examined for age related
assessment. Lipofuscin index (LI) on 10 pairs of right and left eyestalk (20
samples) from samples of 80mm carapace width (CW) yielded paired-sample
student-t test analysis showing LI significantly higher (n = 10, p < 0.001) in the
upper part of male and female eyestalks (39.49 for males & 38.22 µg/mg(protein)
for females) as compared to lower part of male and female eyestalks (19.3 for
males & 19.91 µg/mg (protein) for females). Comparison between right and left
eyestalks for males and females showed significant difference at p = 0.05. Effects
of preservation were measured on 20 wild samples, 7 to 8 cm CW. Ten samples
were analyzed for LF concentration immediately after collection and another 10
after freezing at -80º C for two weeks with LI significantly higher for both males
and females in the frozen samples (p < 0.05). The effect of salinity was measured in seven treatments at different salinities (10ppt, 15ppt, 20ppt, 25ppt, 30ppt, 35ppt,
and 40ppt). 25ppt is the salinity optimum for LF accumulation in both males (58.99
µg/mg (protein)) and females (57.69 µg/mg (protein)). LI-Age relationship was
determined on samples cultured at a hatchery, with LF extracted monthly for a year
period. Correlation analysis between males and females for LI-Age showed no
significant difference at p = 0.05 and a positive linear relationship of LI and age
for both males and females with the regression line LI = 3.5908(t) - 2.4058;
R
2
=0.8071. LI-CW showed no significant difference between males and females
at p = 0.05. The mathematical description of P. pelagicus growth using the von
Bertalanffy growth function (VBGF) demonstrated a relationship Lt = 11.6802 (1e
-0.1343(t - -1.7626)
). Growth parameter estimation using the Chapman method was L∞=
11.6808 cm; K= 0.1343year
and t0 = -1.7626. This study has provided a guideline
for the most suitable site on the eyestalk for extraction, the optimum salinity for
LF accumulation, the relationship of LI and age, the relationship of CW and LI,
and the growth parameter and age structure of the P. pelagicus population.
