Morphological, Histological, and Physiological Responses of Female Orange Mud Crab, Scylla olivacea (Herbst, 1796), Fed with Different Dietary Lipid Levels

The main focus of the study was to assess the effect of lipid levels on the reproduction of the female orange mud crab, Scylla olivacea. Four isonitrogenous feed (~420 g/kg) were formulated with different lipid percentages: $\text{T}1=60\text{g}/\text{kg}$ , $\text{T}2=80\text{g}/\text{kg}$ , $\text{T}3=100\text{g}/\text{kg}$ , and $\text{T}4=120\text{g}/\text{kg}$ . A feeding trial was carried out on 120 matured female mud crabs for 90 days with 30 replicates in each treatment. Based on the morphological, histological, and hormonal analysis of each crab, the performances of each experimental diet were tested. The results of the experiment disclosed positive body weight gain (BWG) and specific growth rate (SGR), with the highest value recorded in crabs that were fed T4 (BWG: $14.43\pm 1.14\text{g}$ ; SGR: $0.10\pm 0.01\%\text{da}{\text{y}}^{-1}$ ). The highest gonado-somatic index (GSI) and hepato-somatic index (HSI) were noted in mud crabs that were fed T4, each with a value of $14.51\pm 1.13\%$ and $5.23\pm 0.55\%$ , respectively ( $P<0.05$ ). The histological assessment revealed that the highest oocyte diameter was recorded in mud crabs fed T4 ( $192.80\pm 21.93$ μm), where the oocyte diameter was correlated with the progesterone (Pg) concentrations in the ovary with $r=0.73$ . Evidence also indicated that Pg and estradiol (E2) are important in the ovarian development in S. olivacea and their concentrations were affected by the lipid levels. An overall analysis revealed that 120 g/kg of lipid in the diet contributes to optimal reproductive performance in Scylla olivacea. Yet, a further experiment is expected to be carried out in the future to determine the nutrient-dose response as 120 g/kg lipid may not be the optimum lipid level for reproductive and growth performance in S. olivacea. Moreover, the extrapolation of data from this study can be used as guidelines in feed formulation for developments in future research in adult crustaceans.