Impact of Different Pond Bottom Soil Substrates on Blue Swimming Crab (Portunus pelagicus) Culture

Abstract

Pond bottom soil quality is an important factor in aquaculture, but studies on the soil quality in crab ponds are very limited. The objectives of this experiment were to investigate the impact of pond bottom soils on blue swimming crab, Portunus pelagicus. Experimental crabs were reared under simulated earthen pond conditions in 0.5×2.5×0.4 m3 fiberglass tanks with different soil substrates. The 4 treatments used were crabs reared with sandy loam (T1), sand (T2) and clay (T3) as substrates (10 cm thick) and without soil substrate (T4). Crabs were fed with shrimp feed at 5 % of body weight per day (twice a day at 0900 h and 1500 h), for 90 days. Each treatment was done in triplicate. The results showed that the average daily growth of crabs reared with the sandy loam or sand as substrates, and without soil substrate were not significantly different (p > 0.05) but these were significantly higher (p < 0.05) than that of using clay as a substrate. The survival rates of crabs reared with different soil substrates were not significantly different (p > 0.05). The feed conversion ratio of crabs reared with clay or sandy loam as substrates were also not significantly different (p > 0.05), but those reared with clay soil were significantly higher (p < 0.05) than that of using sand as a substrate or without soil substrate. In addition, the levels of organic matter, pH and ammonia in the soil of crabs reared with the clay as substrate were higher than those with sandy loam or sand as substrates. This study demonstrated that soil substrate and changing properties due to levels of organic matter, pH and ammonia in the soil affected the growth rate and feed conversion ratio of P. pelagicus crabs.