Among the larger species of crabs that are known to be of commercial value in the Philippines are the Neptunus pelagicus (alimasag) and the Scylla serrata . Both belong to the swimming crab family Portunidae, but the latter has been an incident product of brackish water fishpond.
Occasionally, juveniles are collected in tidal flats and marshes and stocked in fishponds, but usually at their own accord. The recent years, over fishing, of Scylla serrata has threatened the fishery, industry so possibility of culturing them in ponds was given attention.
Biology of Mud Crab
Mudcrab is a swamp crab that spawns in the sea but the larvae are carried by tide along the seashore. Juveniles migrate to the tidal flats and marshy lands along rivers. It becomes sexually mature in the first year of its life after the female undergoes the precopulatory molt which cannot be readily distinguished from ordinary molting. At this stage the abdomen of the female changes from its triangular shape into broad rounded form.
Mudcrab spawns throughout the year with a peak season for about four months staring from the last week of to the third week of September. As early as April, the stage precopulatory molt which cannot be readily distinguished from ordinary molting. At this stage the abdomen of the female changes from triangular shape into broad rounded form.
During spawning season, the fertilized eggs get out of the ovary and attached to the pleopods where they hatch within a few weeks. The eggs hatched into a planktonic zoea. After passing through several zoea stages and a single megalopa stage within about a month, the larvae metamorphose to benthic juvenile crabs that are found crawling in the shallow areas.
The mudcrab is a voracious feeder. It crawls on the pond or seabed searching food or may also be seen swimming on the surface hunting for food. They feed on natural food, such as: algae, decaying animals, crustacean, or decaying matter.
Suitable Crab Farm Site
Mudcrab prefers brackish water ponds with no less than one meter depth of water. It is the usual practice of fishpond operators to stock mudcrab juveniles in newly constructed or partially developed fishponds, although they are also cultivated in developed ones. In fully developed fishponds, some operators placed hollow-blocks along the dikes to prevent the crab from burrowing along the dikes thus causing leakages. These blocks serve as refuge or hideouts when not actively feeding.
Generally, the most suitable places for mudcrab culture are underdeveloped fishponds with numerous high mounts and submerged region which the animal can take shelter.
The culture of mudcrab in the Philippines is only incidental to bangus culture, except in not fully developed fishponds. Young crabs or juvenile stages are allowed to enter in the pond during high tide when water is admitted to the fishpond. In some cases, seeds are purchased from fry collectors or fishermen with size ranging from 2 to 7 cm along the length of the carapace.
They are caught by scissors nets (sakag) along the sandy shores. Young crabs when purchased have no pinchers as they are removed for ease of handling and to prevent them from fighting or hunting each other during transport. This is no problem, whatsoever, because they have ability of regeneration and other pair of pinchers will grow within three weeks after stocking in the ponds.
As previously mentioned, mudcrab are usually cultured along with bangus, the pond management employed is primarily for milkfish. In developed fishponds, where alimango is solely cultured not much preparation on growing the natural food is done but water freshening is made during high tide.
In ponds, alimango aside from feeding on the natural foods can be given artificial feeds like trash fish, kitchen refuse, by products of slaughters houses and other feeds of animal origin.
Alimango reared in ponds, if properly fed can reach marketable size in six months. Alimango are usually harvested using different kinds of traps like “bintol” or liftnets baited with meat or small fish or shrimp or by bare hands. Only the big ones are harvested and the smaller ones are set free in the ponds to attain bigger sizes.
source: DA-BFAR FIDSD flyer