Preventing Fish Diseases
Fish diseases caused by parasites, bacteria or viruses can be spread from pond to pond or from farm to farm by the transfer of infected fish and by animals, people, equipment and contaminated water.
A diseased fish can be recognized by its listless behaviour or by spots on its skin.
Diseases can cause serious problems on fish farms and the farmer could lose most or all his stock.
Simple changes in farm management practices that help prevent the introduction and spread of diseases most times reduce losses.
Biosecurity also applies to fish farms. Proper sanitation, control of movement in and out of the farm, and isolation facility for sick or new stock are all good practices to prevent the introduction and spread of diseases in your farm.
Sources of infection/disease to your fish include equipment, boots, workers, yourself, birds, wild fish, new stock, contaminated feed and water.
Use warm water and detergent to clean equipment such as buckets, boots and vehicles and then dry them.
It is important to know that some disinfectants will not work effectively in the presence of dirt and organic matter such as fish mucus. Equipment must be thoroughly washed before applying disinfectant and sun dry to eliminate remaining bacteria or viruses.
Most detergent-resistant bacteria and viruses can be killed with a broad-spectrum disinfectant
such as sodium hydroxide, formalin, chlorine, iodine, or a peroxide product.
Pond may be drained with all fish and vegetation removed. Add hydrated lime and dry.
Most viruses and bacteria may be killed by adding hydrated lime to raise water pH to 11 for at least 1 hour.
Consult with your veterinarian to determine the best choice of cleaning and disinfecting agents to use on your farm.
Animals and birds
A number of animals that live in or move around fish ponds can carry fish diseases. Birds can transmit diseases to fish via their droppings. This is also of public health concern for those that feed their fish with poultry or bird excreta.
Several species of fish-eating birds can carry the life stages of parasites that develop into parasites of fish.
Control of snails in your fish pond is very essential as they serve as host for fish parasites to develop.
Some farmers use netting of the pond surface to keep birds away from the pond.
The safest water for fish production is water pumped straight from a well to the pond.
Water must be tested to ascertain its quality.
Pond water contains two major groups of substances namely dissolved substances made of gases, minerals and organic compounds; and suspended particles made of non-living particles and very small plants and animals, phytoplankton and zooplankton respectively .
The composition of pond water changes continuously, depending on climatic and seasonal changes, and on how a pond is used.
during the day , oxygen production is increased while carbon dioxide content is decreased through photosynthesis;
during the night , oxygen content of the water is decreased and carbon dioxide content is increased through respiration in the absence of photosynthesis.
Therefore, it is important to feed your fish during the day when there is abundance of oxygen in the pond.
Decomposition of plant and animal matter in the pond reduces available oxygen.
The amount of oxygen that is dissolved in the water is critical for fish and other pond life. The maximum amount of oxygen that can be dissolved is controlled by the water temperature. Warmer water can hold less dissolved oxygen than colder water.
Fish diseases may cause severe losses on fish farms through:
reduced fish growth and production;
increased feeding cost caused by lack of appetite and waste of uneaten feed;
increased vulnerability to predation;
increased susceptibility to low water quality;
death of fish.