Good water quality on tilapia farms depends on a suitable environment to promote growth. Such an environment can be achieved by maintaining the correct balance between feed input and the assimilative capacity of the water. However, the more fish that are grown, the higher the demand on fish production, and various additional factors become necessary to achieve good water quality, writes Bonnie Waycott for TheFishSite.
Environmental requirements of tilapia
Tilapia can grow and reproduce at salinity concentrations of up to 36 parts per thousand, are highly tolerant of low dissolved oxygen (DO) concentrations and ideal growing temperatures are usually between 22C (72F) and 29 C (84F). Best growth rates are achieved between pH 7 to 9, while other variables must also be kept at a safe range to produce tilapia in a cost-effective manner.
Common water quality parameters and how to manage them
Water quality parameters to manage include dissolved oxygen (DO), pH and ammonia, nitrite, aeration, turbidity, alkalinity and hardness. Essential for respiration and decomposition, DO comes from atmospheric oxygen and photosynthesis but because photosynthesis depends on the amount of light available to aquatic plants, it takes time for the oxygen to fully dissolve and for correct levels to be maintained.
Reduced DO can be detected if the fish don't feed well or come to the surface to breathe. DO can be measured electronically with an oxygen meter available from shops dealing with laboratory equipment or kits containing necessary chemicals.
The pH range of the water should be maintained with a soluble carbonate or bicarbonate source, as these are easy to obtain, extremely soluble and safe to handle.
Ammonia and ammonium strongly impact water quality and too high a level can lead to mortality. Concentrations should be around 0.5mg/l by ensuring that pH levels remain at least below 9.0 and maintaining high DO concentrations.
Parameters such as feed quality and rate affect ammonia production, and these must be closely monitored.
Adding agricultural limestone to pond soil or the water's surface also helps maintain alkalinity and hardness, while nitrite levels can be measured using colorimetric test kits with the necessary reagents and a spectrophotometer or colorimeter, available from aquaculture equipment suppliers.
Avoiding toxic chemicals like insecticides and keeping away any agricultural runoff ensures protection, while agricultural limestone or animal manures help to control turbidity from suspended solids and other fine particles.
Another way to trap solids is to use a solids separator followed by a pre-filter that passes water through a barrier material.
Aeration is also important to effectively remove waste and keep the water clean. Various aerators are available such as paddlewheels (these increase the area of water through which oxygen is absorbed), agitators and blowers.
Recirculating systems include a clarifier that removes faeces or uneaten food, while a biofilter eliminates toxic waste products. Plastic media biofilters are also becoming more widespread as they are light and easy to clean.
How often should water quality be monitored? This depends on several factors, such as the density of the fish and whether the culture is high or low intensity. The higher these factors, the more frequently water should be checked.
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