Lipofuscin Levels In The Eyestalks For Age Estimation Of Blue Swimming Crab, Portunus Pelagicus From Setiu Wetlands, Terengganu, Malaysia

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.