Development of semi-moist formulated feed for female orange mud crabs, Scylla olivacea (Herbst, 1796) broodstocks with graded lipid levels

The present study examined the physical characteristics of semi-moist formulated feeds to the reproductive maturation of female orange mud crab, Scylla olivacea. In this study, two experiments were conducted. The first experiment compared four types of natural diets; fish offal (discarded organ), mangrove clams (Polymesoda erosa), black devil snail (Faunus ater), and commercial shrimp feeds (control), to select the basal diet for the formulation of feeds. Proximate compositions of the different diets revealed that the mangrove clam, P. erosa (protein = 81.63 % and lipid = 13.54 %) is the most suitable ingredients for the mud crabs’ diet. Fatty acid analysis also showed that mangrove clams had the highest concentration of ARA, EPA, and DHA at 0.56 %, 1.62 %, and 2.68 % respectively. In the second experiment, four isonitrogenous feed (~42 %) with different lipid percentages; T1: 6 %, T2: 8 %, T3: 10 %, and T4: 12 % were formulated to investigate the effects of the lipid inclusion on maturation of mud crabs. The effects of different levels of lipid on palatability, feed water stability, nutrient leaching, buoyancy, and total solids were studied prior to feeding experimentation. The palatability tests showed high attractability of the crabs towards the feeds. Meanwhile, high water stability (dry matter retention) were recorded in all experimental feeds after long immersion hours, with low nutrient leaching, and low solids disintegration. Later, feeding trial on 120 matured female mud crabs (carapace width: 10.24 ± 0.66 cm and body weight: 186.42 ± 37.90 g) revealed that the semi-moist formulated feeds are readily accepted by the crabs. The crabs from all treatments recorded positive body weight gain (BWG) and specific growth rate (SGR) with crabs fed T4 dominating (BWG = 11.43 g, 14.65 g, and 12.13 g; SGR = 0.35 %day-1, 0.13 %day-1, and 0.08 %day-1 during 30-, 60-, and 90-day of feeding trials respectively) (p < 0.05). Similarly, morphological results showed that high GSI was noted in S. olivacea fed with T4, increasing at subsequent feeding trials (10.44 %, 11.03 %, and 14.51 %) (p < 0.05), which were inversely proportional with the HSI (8.92 %, 5.11 %, and 4.76 %) (p < 0.05) compared to other treatments, probably contributed by the high percentage of lipid inclusion. These findings demonstrate that diets contained 12 % lipid and 42 % protein (T4) is ideal for somatic and reproductive growth of S. olivacea. Yet, a nutrient dose-response study is expected to be carried out in the future to estimate the optimum lipid level required for reproductive and growth performance in S. olivacea.