Several Causes of Fish Gasping at the Surface and Their Prevention and Treatment Methods

Fish "gasping at the surface" is a phenomenon that frequently occurs in aquaculture production, and it is also an important sign for judging whether fish are diseased and whether water quality has changed. However, many farmers, after discovering pond fish "gasping at the surface," do not understand the cause and simply apply medication based on "experience," which often proves ineffective and may even cause mass mortality. In fact, fish "gasping at the surface" can be caused by multiple factors. According to the cause, "gasping at the surface" can be divided into the following 3 types.

1. Hypoxia-induced gasping

Hypoxia-induced gasping is the phenomenon of "gasping at the surface" formed when the dissolved oxygen content in the water is too low and cultured fish swim to the relatively higher surface water layer to breathe. This type of "gasping at the surface" is characterized by a concentrated occurrence time and a wide range of affected species. It generally occurs from the early morning hours to 8-9 AM in summer. If the degree of hypoxia is high, all fish in the pond will be affected or even die. However, if it is only mild hypoxia, then possibly only fish with high oxygen consumption rates will gasp at the surface, and they will return to normal after strong light and high temperatures.

Continuous rainy weather, low atmospheric pressure, and the period after summer rainstorms can all cause gasping at the surface, while the common causes in aquaculture production are high stocking density and overly fertile water quality. Although the large amount of algae in fertile water releases oxygen through photosynthesis during the day, which can make the dissolved oxygen in the water very high, at night without photosynthesis, the large number of pond fish, algae, and organic matter in the fertile water also consume a large amount of oxygen, causing the dissolved oxygen to fall below the tolerance point of the fish and causing fish to gasp at the surface.

For fish gasping at the surface, zeolite powder, "Futouling" or industrial-grade hydrogen peroxide should be applied for rescue, and the aerator should be turned on. The main prevention methods include: reducing stocking density; regularly adding clean water to prevent the water quality from becoming overly fertile; and turning on the aerator at noon on sunny days to repay the "oxygen debt" of the bottom water, so as to prevent nighttime hypoxia, etc.

2. Gasping at the surface caused by ammonia poisoning

This type of gasping at the surface is actually a stress response caused by fish poisoning due to excessively high ammonia concentration in the water. This type of gasping at the surface, like hypoxia-induced gasping, can affect all fish. However, because the daily variation of ammonia is not as obvious as the daily variation of oxygen, gasping at the surface will continue to occur throughout the day, and it is more serious when the water temperature is high in the afternoon. This type of gasping at the surface mainly occurs from early winter to early spring. This is because at this time a large amount of algae dies and decomposes, photosynthesis is weak, and the ammonium salts produced by the decomposition of residual bait in the water and fish excretion cannot be transformed, resulting in ammonia accumulation and causing fish poisoning. For this type of gasping at the surface, emergency treatment can be carried out by adding new water, turning on the aerator, and splashing coarse salt or bottom water quality improver, or after the beginning of winter, water quality improvers such as bottom water quality improver or zeolite powder can be regularly splashed for prevention.

3. Gasping at the surface caused by disease

This type of gasping at the surface is due to fish leaving the group and swimming alone at the water surface because they are diseased. Fish gasping at the surface are generally scattered in the shallow water near the pond edge, with no obvious seasonal occurrence. The difference between this type of gasping at the surface and the previous two types is that the number of fish gasping at the surface is small, and generally it is not explosive. Since this type of gasping at the surface is caused by disease, prevention and treatment should be combined with fish disease prevention and treatment measures and targeted at the cause of the disease.