Key Technical Points for Winter Management in Fish Farming

Since fish metabolism is closely related to water temperature, their peak growth period is mainly in summer and autumn. In winter, because pond water temperatures are generally low, fish activity decreases, fish feed less, metabolism becomes very slow, and growth rate slows accordingly. Combined with natural consumption, the fish body weight actually decreases. In addition, pond contracts are often on an annual basis, so at this time most adult fish must be rushed to market before overwintering. The fish left to overwinter are mainly fry or broodstock. The overwintering problem of farmed fish is an important part of fish farming production. How to ensure the safe overwintering of fingerlings and broodstock is a key issue in fish farming as a sideline. Therefore, correct methods and measures for safe overwintering of fish must be determined. Safe overwintering measures for fish should be based on specific local conditions as well as local overwintering experience and problems from previous years, and corresponding effective overwintering measures should be adopted. The effective experience and measures from various places regarding safe overwintering of fish are summarized in the following aspects:

Preparation Before Overwintering

1. Pond clearing and disinfection. Preparatory work for fry overwintering should be carried out around October each year. The size of the overwintering site should be chosen according to one's actual conditions, trying to select a site facing south with sufficient sunlight, convenient drainage and irrigation, an area of more than 1 mu, and a water depth maintained at more than 80 cm. Broodstock ponds should be larger, generally more than 5 mu, with a water depth of 1.5 m. For ponds preparing to stock overwintering fry, the pond should be cleared and disinfected before fish are released. It is best to drain the water and sun-dry for one week, and deal with silt more than 15 cm thick (using a silt pump, flushing with flowing water, or carrying it out of the pond by shoulder pole). Pond clearing and disinfection of overwintering ponds is the same as before releasing fry in other seasons, and quicklime, tea seed cake, or strong chlorine powder (bleaching powder) can be splashed. This mainly kills viruses, bacteria, trash fish, and other natural enemies. Note: tea seed cake should first be crushed, soaked for 2-3 days, then brewed with boiling water, fully stirred, and splashed over the whole pond together with the residue and liquid. Quicklime and strong chlorine powder (bleaching powder) should be mixed with water and splashed over the whole pond.

2. Preparation of fingerlings. The species stocked for overwintering fry should suit local conditions and adapt to one's own pond conditions and market needs. If the pond water temperature can remain above 12°C and the water depth can remain above 1.5 m, it may be appropriate to consider stocking some warm-water fish such as wild mud carp, mud carp, and tilapia. If in previous years mud carp could not overwinter safely, then warm-water fish need not be considered. Under normal circumstances, for each mu of water surface, the average water depth should be more than 1.2 m.

Enhancing the Constitution of Overwintering Fish

1. Increase fatness. Before overwintering, feed carefully and intensively to increase fat accumulation. Feeding in the month before overwintering is the key period for safe overwintering, called the "fattening period." If feeding during the "fattening period" is done well, safe overwintering of fish is fairly assured. Therefore, before overwintering, fish should continue to be fed until they stop feeding.

2. Select and cultivate excellent cold-resistant varieties: in high-altitude cold regions, there should be planned selection and cultivation of varieties with relatively strong overwintering ability that can adapt to cold environmental conditions.

3. Strictly observe quarantine and disinfection measures. Ensure overwintering fish are healthy and uninjured. Before overwintering, quarantine work should be strengthened. Fish that do not meet overwintering requirements should be handled separately. Fingerlings that are small in size and weak in constitution should not be placed into flowing water or overwintering waters with many enemies. When entering overwintering ponds, all should undergo drug disinfection to prevent fish diseases from spreading and causing disaster during the overwintering period.

4. When leaving the pond, entering the pond, and during transport, operate carefully and try to avoid injury.

Improving the Environmental Conditions for Fish Overwintering

1. Carefully choose overwintering waters: there should be little bottom silt, strong water retention, and easy catching. There should be a deep pool, water depth above 1.5 m, and water quality suitable for overwintering conditions.

2. Improve and create good overwintering environmental conditions. For still-water overwintering ponds, snow on the ice surface must be cleared at any time to maintain clear ice, which plays a positive role in biological oxygenation.