Principles of fish health management

The concept of fish health management is that fish cultured under such conditions will achieve optimal growth rate, feed conversion rate, reproduction rate and survival rate. Maintaining a high quality aquatic environment and feeding nutrient-balanced diets are important for maintaining fish health and preventing fish disease. Proper fish health management targets environmental, nutritional, economic, and other factors to prevent fish disease rather than treat it. Here are some basic principles for fish health management.

First, we must manage the environment. To maintain the good health of fish, maintaining water quality within the limits of non-stress to fish is the primary task. Aquaculture producers should manage the most important water quality factors, such as dissolved oxygen, carbon dioxide, water temperature, water pH and ammonia, to ensure that water quality conditions that cause stress to fish do not occur. The accumulation of fish excreta, uneaten feed and exogenous pollutants in the aquatic environment is the main cause of deterioration of water quality. Feeding fish with sinking or floating pellets that meet rather than exceed the nutritional requirements of fish and are stable in water produces less waste. Fish should be fed with high quality pellet feed with a feed coefficient between 1.0 and 1.7, depending on the species and age of the fish.

The concept of fish health management is that fish cultured under such conditions will achieve optimal growth rate, feed conversion rate, reproduction rate and survival rate. Maintaining a high quality aquatic environment and feeding nutrient-balanced diets are important for maintaining fish health and preventing fish disease. Proper fish health management targets environmental, nutritional, economic, and other factors to prevent fish disease rather than treat it. Here are some basic principles for fish health management.

1. Environmental management is required. To maintain the good health of fish, maintaining water quality within the limits of non-stress to fish is the primary task. Aquaculture producers should manage the most important water quality factors, such as dissolved oxygen, carbon dioxide, water temperature, water pH and ammonia, to ensure that water quality conditions that cause stress to fish do not occur. The accumulation of fish excreta, uneaten feed and exogenous pollutants in the aquatic environment is the main cause of deterioration of water quality. Feeding fish with sinking or floating pellets that meet rather than exceed the nutritional requirements of fish and are stable in water produces less waste. Fish should be fed with high quality pellet feed with a feed coefficient between 1.0 and 1.7, depending on the species and age of the fish.

Maintaining fish health depends on the combination of several management factors. To maintain good fish health, management of water quality, fish nutrition and environmental waste inputs must be integrated with other stock management measures. These measures include: (1) the use of fish stocks of high genetic quality. (2) Use pathogen-free fish stocks. (3) Use drugs and chemicals only when necessary to treat and control fish diseases.

3. Avoid fish stress. Most infectious fish disease pathogens occur naturally in aquatic environments, and infection by pathogens usually occurs only when fish are stressed. Stress is a condition caused by any environmental or other factor that causes an animal to adapt beyond its normal range or impairs its normal function of maintaining good health. Therefore, factors that cause stress in fish should be avoided. Common stress factors in cultured fish include the following: (1) Low dissolved oxygen syndrome (LODOS). Low dissolved oxygen syndrome is the most common water stress factor in cultured fish. Hypooxygenation syndrome arises from lack of oxygen in water. 2) Too much carbon dioxide. Excessive carbon dioxide affects the health of fish by reducing the ability of fish blood to transport oxygen. Excessive carbon dioxide interferes with fish respiration, increases the minimum oxygen concentration that fish can tolerate, and makes water acidic. Acidification of water causes pH to decrease, increasing stress on fish. (3) Extreme pH values. Fish farming requires a pH range of 6.5 to 9.0. If the pH value of water exceeds this optimal range, fish will be stressed and their health will be seriously damaged. (4) Low alkalinity (calcium carbonate content <20 mg/L). Low levels of calcium carbonate (CaCO3) in aquaculture waters can severely affect the pH of the water, creating acidic stress conditions in the morning hours and alkaline stress conditions in the evening hours. (5) Severe changes in water temperature. Fish will die due to stress in water with drastic changes in water temperature. (6) Increase in ammonia. Nonionic ammonia is toxic to fish. Ammonia is an excretory waste product of fish metabolism. The amount of ammonia in aquaculture systems depends on the level of ammonia excreted by fish. (7) Nitrite increase. Low concentrations of nitrite in the water environment can poison fish. The increase of nitrite concentration in water generally occurs at the same time as the increase of ammonia concentration. When plankton suddenly die in large quantities, ammonia content levels will rise suddenly. During the late autumn, winter and early spring months, ammonia assimilation decreases and ammonia concentrations increase significantly due to lower water temperatures. (8) Hazard of pollutants. Long-term exposure of fish to sublethal levels of contaminants can impede fish growth and reduce resistance to disease. The presence of pollutants from industrial and municipal wastewater in aquaculture waters can cause chronic stress in fish, reducing their health levels and growth rates. (9) Excessive operational activity. Excessive or inappropriate manipulation is one of the most common and serious stress factors in cultured fish. It increases the respiration, metabolism and other physiological activities of fish. Excessive manipulation will damage the protective mucosa and tissues of fish, resulting in bacterial invasion.

Reasonable nutrition is essential for maintaining fish health. Pellet feed formulations for fish must provide the protein, energy, vitamins, minerals and other nutrients necessary for a particular fish species and must not feed old and moldy feed.