Salinity Requirements for Mud Crab Aquaculture | Aquaculture Technology
Mud-crab or Scylla sp. is a type of aquatic invertebrate which lives in the water for most of the time. One of the important properties that fit them in the aquatic animal classification is the ability to breathe through gills that gets the dissolved oxygen in the water. Therefore, it is essential to know the ideal water quality to farm them to prevent the loss of profit. In this article we will look into one of the most important and the basic of farming this species, salinity. Salinity is the concentration of salt in the water, measuring in the unit of parts per thousand (ppt). The salinity of freshwater is 0 ppt and the salinity of sea water is 35ppt. The Scylla sp., is often farmed in a condition where we call brackish water, which the salinity is between freshwater and seawater, between 10-30ppt. The 4 different species of Scylla sp., even though are all mud-crabs, each has a different salinity that is ideal to farm them, due to the different areas and different zones that each of them dominates.
Generally mud-crabs could tolerate a wide range of salinities. In fact, they are able to survive in freshwater for a few hours, this enables us to be able to disinfect them in freshwater, killing any harmful bacteria that could only survives in saline water. The mud-crabs prefer salinity of 15-25 ppt. It is essential to understand the ideal salinity range to be able to optimize the growth and minimize the mortality of the specific species of the mud-crabs being farmed.
Scylla serrata, often known as the Sri-Lankan mud-crabs are the most popular species to be farmed due to its fast growing ability. They could be found in mangrove forests flooded with full salinity seawater all year round. Therefore, farming Scylla serrata would require water with higher salinity at 25-30ppt.
Scylla paramamosain, with obvious light-green claws, is very popular and has a high demand in China and Singapore. Often found abundantly in South China Sea and Java Sea, residing in mangrove forests and subtidal flats. Similar to Scylla serrata, they prefer a higher range of salinity compared to the mud-crab species.
Scylla olivicea, easily distinguished from their orange-colored claws, often found residing in subtidal flats with a lower salinity range of brackish wat