What are the basic principles of fish health management

The concept of fish health management is that fish raised under such conditions will achieve optimal growth rate, feed conversion rate, reproduction rate and survival rate. Maintaining a high-quality aquatic environment and feeding nutritionally balanced feed are very important for maintaining fish health and preventing fish from becoming diseased. Proper fish health management should aim at environmental, nutritional, economic and other factors to prevent fish diseases rather than focusing on treating fish diseases. The following are some basic principles of fish health management.

1. The environment must be managed. To maintain good health in fish, keeping water quality within limits that do not stress the fish is the primary task. Aquaculture producers should effectively manage some of 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 stress fish do not occur. The accumulation of fish excreta, uneaten feed and external pollutants in the aquatic environment is the main cause of deteriorating water quality. Using sinking or floating pellet feed that meets but does not exceed the nutritional needs of fish and has good stability in water to feed fish produces less waste. Fish should be fed high-quality pellet feed according to differences in species and age, and the feed conversion ratio should be between 1.0 and 1.7.

The concept of fish health management is that fish raised under such conditions will achieve optimal growth rate, feed conversion rate, reproduction rate and survival rate. Maintaining a high-quality aquatic environment and feeding nutritionally balanced feed are very important for maintaining fish health and preventing fish from becoming diseased. Proper fish health management should aim at environmental, nutritional, economic and other factors to prevent fish diseases rather than focusing on treating fish diseases. The following are some basic principles of fish health management.

1. The environment must be managed. To maintain good health in fish, keeping water quality within limits that do not stress the fish is the primary task. Aquaculture producers should effectively manage some of 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 stress fish do not occur. The accumulation of fish excreta, uneaten feed and external pollutants in the aquatic environment is the main cause of deteriorating water quality. Using sinking or floating pellet feed that meets but does not exceed the nutritional needs of fish and has good stability in water to feed fish produces less waste. Fish should be fed high-quality pellet feed according to differences in species and age, and the feed conversion ratio should be between 1.0 and 1.7.

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

3. Avoid stress in fish. The pathogenic organisms of most infectious fish diseases exist naturally in the aquatic environment, and fish are usually infected by pathogens only after they have been stressed. Stress is a state caused by any environmental factor or other factor that pushes an animal's adaptive response beyond the normal range, or impairs the animal's normal functions for maintaining good health. Therefore, factors that cause stress in fish should be avoided. Common stressors for farmed fish include the following: (1) Low dissolved oxygen syndrome (LODOS). Low dissolved oxygen syndrome is the most common water quality stressor for farmed fish. Low dissolved oxygen syndrome originates from oxygen deficiency in the water. (2) Excess carbon dioxide. Excess carbon dioxide affects fish health by reducing the ability of fish blood to transport oxygen; excess carbon dioxide hinders fish respiration, raises the minimum oxygen concentration that fish can tolerate, and makes water quality acidic; acidification of water quality leads to a decrease in pH and increases stress on fish. (3) Extreme pH values. Farmed fish require a water pH range of 6.5 to 9.0; if water pH exceeds this optimal range, it will stress fish and seriously damage fish health. (4) Low alkalinity (calcium carbonate content <20 mg/L). In aquaculture waters, a low content of calcium carbonate (CaCO3) will seriously affect water pH, creating acidic stress conditions during the morning hours and alkaline stress conditions during the evening hours. (5) Severe changes in water temperature. In water bodies where water temperature changes drastically, fish will die from stress. (6) Increase in ammonia. Non-ionized ammonia is toxic to fish; ammonia is an excretory waste product in fish metabolism, and the ammonia content in aquaculture systems depends on the level of ammonia excreted by fish. (7) Increase in nitrite. Low concentrations of nitrite in the aquatic environment can poison fish; an increase in nitrite concentration in water generally occurs together with an increase in ammonia concentration, and when plankton suddenly die in large numbers, ammonia levels can suddenly rise. In the months of late autumn, winter and early spring, because water temperature is lower, ammonia assimilation decreases, and ammonia concentration can also increase noticeably. (8) Harm from pollutants. Long-term exposure of fish to sublethal levels of pollutants hinders fish growth and reduces resistance to disease. The presence of pollutants from industrial and municipal wastewater in aquaculture waters can cause chronic stress in fish and reduce fish health and growth rate. (9) Excessive handling activities. Excessive or improper handling activities are one of the most common and most serious stressors for farmed fish; they increase fish respiration, metabolism and other physiological processes, and excessive handling activities can damage the protective mucous membrane and tissues of fish, thereby leading to bacterial invasion.

4. Reasonable nutrition is necessary for maintaining fish health. Pellet feed formulas for fish must provide the required protein, energy, vitamins, minerals and other nutritional elements for a particular fish species, and stale and moldy feed must not be fed.