Guidelines for Fishery Reconstruction Measures After Rain, Snow and Freezing Disasters in Southern China

Since early January 2008, rain, snow and freezing weather has severely affected fishery production in multiple provinces and municipalities in southern China. According to incomplete statistics, losses from fish and shrimp killed by freezing in southern provinces and regions exceeded 10 billion yuan. In response, the following measures and suggestions for freshwater fishery reconstruction after rain, snow and freezing disasters in southern regions are proposed for reference.

Types of Damage

In terms of aquaculture species and regions, the current damage is mainly divided into the following types:

1. Tilapia aquaculture: The tilapia aquaculture industry suffered the most severe losses during this winter's cold wave invasion. In some major production areas such as Guangdong and Guangxi, pond-raised tilapia in ponds with water depth less than 2.5 m were basically killed by freezing (except those in covered greenhouses and some cold-resistant varieties).

2. Mandarin fish aquaculture: The main problem affecting the mandarin fish aquaculture industry is that all forage fish were killed by freezing, leaving tens of thousands of tons of mandarin fish in ponds with no forage fish to eat.

3. Other quality fish species: Some quality fish species with poor cold tolerance, such as Thai snakehead, Australian snakehead, jade perch, and some estuarine fish species, also suffered severe losses in this cold winter.

4. @#@234@#@ industry: The most severely affected in this disaster was the Macrobrachium rosenbergii aquaculture industry, and Pacific white shrimp also suffered losses to a certain extent.

5. Traditionally farmed mud carp: Due to prolonged low temperatures this year, combined with large amounts of cold rain, most of the fish were killed by freezing.

6. Devastating impact on seedling production farms: The severe cold caused most freshwater seedling farms in southern regions to suffer varying degrees of damage, which will put pressure on the next step of production recovery.

Disaster Mitigation and Production Recovery Measures

Objectives of disaster mitigation and production recovery measures: (1) Ensure that affected farmers have stable income in the year of production recovery. (2) Bring production back to normal operation as soon as possible. (3) Increase effective social supply and ease the upward pressure on social food prices caused by the disaster.

1. Tilapia production recovery

(1) Overwintering seedlings should be stocked at low density to increase growth rate and strive for early market launch. When water temperature stabilizes above 18°C, seedlings can be stocked. It is recommended to stock 700 to 1,000 fish per mu, which can reach market size of over 500 g per fish from August to October.

(2) Early breeding, early grading, early market launch, striving for three crops in two years. Hatcheries with plastic greenhouse coverage or other heat preservation facilities can strive for early breeding of tilapia seedlings and low-density stocking of graded seedlings to achieve market launch as early as possible in the same year (October to November). At the same time, by using the supporting seedling cultivation technology of multiple ponds, strive to raise three crops of tilapia for market in two years.

(3) After freezing, fish are prone to saprolegniasis, so drugs should not be used indiscriminately, especially malachite green, gentian violet, etc., to avoid product quality and safety problems that affect the development of the entire industry.

2. Mandarin fish production recovery

(1) Breed common carp and crucian carp early and grade them quickly to solve the forage fish supply for mandarin fish.

(2) Collect three types of mud carp (mud carp, Thai wild carp, Mrigal carp) from reservoirs or deep ponds as broodstock, intensify cultivation, and strive to bring fish fry farms and other seedling systems back to normal production levels as soon as possible.

3. Other quality fish species can be adjusted, such as snakehead (snakehead murrel), @#@243@#@ and other fast-growing market varieties, so that fish farms can continue to operate normally.

4. In the recovery process of ponds that raise the four major Chinese carps after large numbers of mud carp were killed by freezing, the stocking amount of grass carp and crucian carp can be appropriately increased to maintain total output.

Management Measures for Early Spring Production Recovery

As the severe winter passes, the current air temperature and pond water temperature will rise slowly. With rising temperatures and the alternation of cold and warm air currents in early spring, the following aspects of daily pond management should be done well:

1. Dead fish in ponds should be promptly removed and can be used as base fertilizer for fruit and other planting industries, or subjected to harmless treatment. Quicklime and bleaching powder should be applied around the pond for disinfection.

2. On sunny days with sufficient sunlight, the pond water level can be appropriately lowered to speed up the rise of pond water temperature.

3. When southeasterly winds and long periods of overcast and rainy weather occur, and water temperature is 16°C to 22°C, Moina in ponds can easily reproduce in large numbers, very easily causing oxygen deficiency and pond turnover. Close attention should be paid. Once discovered, trichlorfon or insecticide should be used promptly for control. At the same time, aerators should be turned on to increase oxygen.

4. On sunny days with high temperatures, aerators can be turned on at noon to speed up the rise of pond water temperature and increase dissolved oxygen in pond water.

5. Early spring is the season for protozoan diseases, such as trichodina and epistylis. Frequent inspections should be carried out, and once discovered, timely treatment should be given to avoid secondary bacterial diseases.

Suggestions

The losses caused by this low-temperature disaster weather were enormous, exposing weaknesses in applied basic research. In the future, research and investment should be strengthened in the following areas:

1. Strengthen research on the selection, breeding, promotion and application of cold-resistant varieties.

2. Strengthen the basic construction of ponds. For example, some renovated ponds with a water depth of 3 m to 4 m suffered relatively lighter losses in this freezing disaster. Therefore, strengthening pond renovation is very necessary.

3. The disaster prevention and mitigation mechanism involving meteorological, administrative, research institutes, universities and other technical departments should be further improved to respond to disasters.