Water Quality Management For Aquaculture

Water sources is vital factors in aquaculture environment because the best water quality will results in high production yield with low rate of aquaculture problems. Proper culture management will ensure that the hatchery is free of disease. Disease can cause mass mortalities to the culture stocks at all stages. And as the reason, the disease outbreak will mainly from the water itself which is contaminated from where it initially comes or from any material used as well as from the surrounding air at the hatchery. The disease also can spread from contaminated feed for the stock consumption.

The hatchery infrastructure must be design appropriately and must allow cleaning and disinfecting activities to be carry out. The incoming water should be treated and disinfected through chlorination and filtration before it can be distributed to any different working areas at the hatchery. Distribution of water should also be designed to avoid any cross contamination. The water pipes, as well as the air lines, should also be set-up to allow overall cleaning and disinfecting and allow the disinfecting solution to be pumped in inside those structures and easily to complete the process during dry-outs session.

The most common primary filter in the hatchery is the sub-sand wells, which is used to filter raw seawater entering the hatchery. They are the favourable primary filter and they helps a lot in limiting fouling organisms, pathogen hosts, red tides and pathogens in which direct system is lacking. Next, the sea water must to pass through sedimentation process to remove any suspended solids especially any sediment substances.

The water is then to be chlorinated using hypochlorite solution (sodium or calcium) for 10ppm active ingredient for not less than 30 minutes. Chlorination is important in the water treatment to stun and kill any pathogens present inside the existing water. The next water treatment is through ozonation, UV light before the water is kept in the reservoir. The water in the reservoir must be checked to ensure there is no chlorine residuals remain inside the holding water. The chlorine test can be conducted using ortho-toluidine, 3 drops for 5mL of water sample. The water sample will turn into yellowish colour to indicate that the water still contains chlorine substance.

To deplete any chlorine substances left inside the water in the reservoir, sodium thiosulphate can be added at the same amount of total chlorine residue in the water (1ppm thisulphate to 1ppm chlorine). Before the water can be transfer to the reservoir, EDTA or any chelating agents should be applied to chelate any heavy metals which might present inside the water. The quantities of the EDTA is depends on the concentration of heavy metals present. For spawning and hatching tanks, extra EDTA is required at up to 20-40ppm to ensure that there are totally free of heavy metals and Treflan at 0.05-0.1ppm is applied to kill any fungi presences inside the water.

The water temperature for all tanks in the hatchery should come into consideration, as each area needs their own specific temperature to maintain their optimum growth and sustainability. Boiler, heater or any heat exchange system is required to increase the water temperature while a chiller system will help to decrease the water temperature. All these equipment must be installed just before the water from reservoir enters into the respective tanks. Each hatchery unit have different needs of water temperature. This is also applied for the size of the filtration used to filter the incoming water to the tanks.

The recommended standard sizes filtration and favourable temperature for each working area is referred as stated;

Working Area	Filter Size (mm)	Temperature (˚C)
Maturation Tank	15	28-29
Spawning Tank	0.5-1.0	29-32
Hatchery Tank	5	28-32
Algae Culture (indoor/pure)	0.5	18-24

Recommended standard mesh size of water filter and water temperature for each working area.

For hatchery with the re-circulating water system, cross-contamination can easily occurred between tanks and between every working area. To prevent this to happen, separate re-circulating system should be used for each area which required this system. This system is the most efficient system for broodstock maturation tank as they reduce the need for water replacement and residual water discharge. Re-circulation system helps to maintain stable physical and chemical parameters in the water. Besides, it also helps in concentrating mating hormones in maturations, as well as provides better biosecurity.

If the re-circulating system is employed, additional biological filters are required for each area of the hatchery as they are able to remove any dissolved organic materials found inside the water. There are many types of biological filters apply at the hatchery, where all filters are incorporate with living materials such as the denitrifying bacteria that must be cultivated prior to use, they are also require periodic cleaning in a way that does not kill the beneficial bacteria inhabitants.

For conclusion of the water quality management, it is important that all incoming water, tanks and materials must be cleaned, treated and disinfected before they can be distributed or used. Besides, all pipes and lines installed at the hatchery must be design to avoid any cross-contamination from occurred. Temperature and salinity most be control respectively to each area. The rules also applied to the filtration system. All of these methods must be accomplished to ensure optimum conditions are met at all time.