Preparation of basic facilities such as spawning tanks, hatching tanks, larval rearing tanks, water supply and aeration systems is one of the most important activities in any hatchery operation. Hatchery production declines if maintenance and preparation of these facilities are not well done.
Spawning, hatching, larval rearing and nursery tanks are basic requirements in any hatchery and preparation of such tanks prior to operation are accomplished in two ways:
Newly constructed hatchery
Tank facilities especially concrete ones in a newly constructed hatchery must be conditioned first before any hatchery operation is done. Alum (Potassium aluminum sulphate), a cheap chemical, can be used to neutralize tanks. The newly constructed tanks are first filled up with sea or freshwater, small pieces of alum are then broadcasted into the tanks at a rate of 250 g/cubic meter and allowed to stand for about one week. Fiberglass or wooden tanks can be conditioned by filling up with water until the pH of the water in the tanks are stabilized.
Operational hatchery
Occasionally, larvae in operational tanks get infected by diseases. To deter such occurences, tanks must be properly cleaned with freshwater, dried and exposed to the sun for at least one day prior to stocking. After every run or every other run of operation, the tanks should also be disinfected with 12% sodium hypochloride solution at the rate of 200 ppm for 24 hours.
When the tanks are ready, filtered fresh/seawater is introduced and aeration is checked especially in the spawning and hatching tanks. Strong aeration is necessary to float shrimp eggs owing to its demersal nature. If aeration isnot strong-enough, eggs will sink and mix with the scum at the bottom resulting in low hatching rate.
Water, being one of the most important factors in hatchery operation, must be regularly monitored for important physico-chemical parameters, viz: salinity, pH, N-NO2 temperature. Often times, turbid water flowing out from the sand filter is bacteria laden. This occurs when detritus, small organisms and dirts pass through the filters under high pressure. To avoid this, initial water passing through the filter must be drained off for about 20–30 minutes or until water becomes clear. Disinfection of the sand filter with 12% sodium hypochloride solution at least once a month will help in keeping the filter clean.
It is important that the air from the air blower is oil free. The strength of aeration can be adjusted according to particular need.
Filter box is a standard water filtering equipment normally used in water management. It is used in larval rearing or nursery tank to prevent the larvae from being drained out during change of water. The filter box is made up of nylon netting screen with PVC or wooden frame of size 60cm × 160 cm for shallow and smaller tanks. The mesh size of the screen depends on the size of the larvae, e.g. 80m for protozoea stage, 150–200m for mysis and postlarval stages. The filter box can be hooked on to the side wall of the rearing tank. The draining system consist of a reversed “h” pipe (Fig. 25, 26) with the shorter pipe inside the box and the longer pipe with the lower end attached to rubber hose and the upper end closed with a rubber cap. During operation, water is allowed to fill-up the pipes through the rubber hose. The upper end is then capped in. The lowering of the other end of the rubber hose to the floor facilitates the draining of water from the tank by simple siphon.
