Causes of dead fish in fish ponds in winter

This is the document provided by the county agricultural information center.

There are many reasons for the death of fish during the wintering period, and in most cases it is the result of the comprehensive action of many factors, but one of them often plays a leading role. Therefore, we must comprehensively and concretely analyze the causes of fish death and take effective measures.

First, the overwintering water body is seriously deprived of oxygen.

In general, severe hypoxia in overwintering water is the main cause of fish death. The reasons for hypoxia are as follows:

(1) The pool water is thin, the number of phytoplankton is small, the transparency of ice is poor, and the oxygen produced by photosynthesis is not enough.

(2) There are too many organic matters in the overwintering water, and a large number of them decompose and consume oxygen.

(three) too many wild fish or low fish density caused by hypoxia.

(4) The water-holding capacity of soil is low, and the water level drops too much after freezing, resulting in hypoxia.

(5) Sewage from the factory and water containing various minerals flow into the overwintering water body, and lack oxygen due to high oxygen consumption.

In addition, the stratification of overwintering water body causes the deterioration of bottom water and lack of oxygen.

1. In winter, the bottom water temperature is generally 3-4℃, but the surface water density is relatively small. In addition, the winter ice age in northern China is long, and there is no convection and fluctuation in the pool water, resulting in slow circulation of the pool water and long-term failure to improve the bottom water.

2. Pond fish usually congregate in the deep water area of the pond, and the metabolites discharged from wintering will be enriched in the deep water area. In addition, when the weather turns cold in winter, most of the plankton die and sink to the bottom of the sea. They are deposited in the mud at the bottom of the pond together with fish excrement, residual bait and organic fertilizer, and slowly decompose and consume dissolved oxygen, and the overwintering fish also consume dissolved oxygen, so that the deep water area is gradually in a state of hypoxia.

3. Under anoxic conditions, the organic matter at the bottom of the pond is easy to produce toxic gases under the action of anaerobic bacteria. Such as H2S and NH3. And nitrogen is also easy to exist in the form of nitrite ion, which has an important impact on the normal metabolism of fish, easily leading to fish poisoning and decreased immunity, leading to fish death.

Second, fish are in poor health.

The overwintering pond fish have poor physique and weak tolerance to stimulation caused by external environmental changes, resulting in more and more pond fish deaths.

With the improvement of intensive fish farming procedures, the quality of fish feed must also be improved accordingly. However, some feed production enterprises unilaterally pursue the growth rate of fish, cut corners in the selection of raw materials by adding excessive growth promoters, and ignore the internal quality of products, resulting in poor physique of fish in ponds and easy death during wintering.

In addition, fish overwinter with diseases, such as mild enteritis and rotten cheeks; Fish are injured and susceptible to water mold and ichthyosis during overwintering; Small melon worm; A large number of parasites such as rotifers and giant salamanders are infected; Especially in late winter and early spring, various bacterial diseases and bubble diseases occur from time to time, resulting in different degrees of dead fish. Specifically:

1. Before putting the fish into the overwintering pond, there is no strict disinfection or incomplete disinfection, and the fish body is not disinfected according to the conventional method before entering the pond, and symptomatic drugs are fed to prevent the fish body from overwintering with diseases.

2, there is no right medicine, timely treatment. Inspection was not strengthened during the wintering period, and sick fish were not used in time.

Third, poor management.

Insufficient careful management during the wintering period, failure to check dissolved oxygen, fish activities and water level changes in time, or failure to take timely measures after finding bad conditions, resulting in a large number of dead fish. For example: the overwintering pool leaks, the water is too shallow or frozen to the end, and the fish are all dead; The dissolved oxygen was not checked regularly before and after the Spring Festival, and the fish died of lack of oxygen. Improper management measures, such as paying attention to ice drilling but not to snow sweeping, can not solve the problem of lack of oxygen in pool water, and fish die of lack of oxygen; In order to increase the dissolved oxygen in the pond, the water temperature of the pond water is rapidly reduced to below 0.5℃ by circulating the pond water for a long time, and the fish are frozen and dizzy, freezing to death; In some cases, at the end of overwintering, the dissolved oxygen or carbon dioxide in the pool is too high, so it is impossible to take measures to reduce the gas by water injection, which leads to the fish in the pool suffering from bubble disease and dying.