Overwintering and seed conservation techniques of cultured tilapia in greenhouse

Tilapia is a tropical fish, its cold resistance is relatively poor, generally, when the water temperature drops to 12 ℃, tilapia will appear frostbite or freeze to death. Oreochromis niloticus has relatively strong cold resistance, but it can not survive the winter in a low temperature environment for a long time. In China, except for Hainan, Taiwan, Yunnan and Guangdong Province, most areas of tilapia can not survive the winter in the natural environment. Corresponding measures for overwintering and seed conservation should be taken to ensure the smooth overwintering of parents and seedlings.

There are many ways for tilapia to overwinter. according to the differences of local climate and overwintering conditions, there are mainly covering film ponds and greenhouses, hot spring water overwintering, deep well, factory waste heat, boiler heating and electric heater heating and so on. As the production base of tilapia seedlings, our institute basically adopts the overwintering method of covering film, big pond greenhouse and iron frame cover film according to the overwintering experience in the past few years. Practice has proved that this is a more successful overwintering technology.

Preparation before overwintering

1. Selection and preparation of overwintering ponds

Overwintering ponds are required to choose higher topography, good water retention, leeward to the sun, the area should not be too large, generally less than 6 mu, for east-west direction, the span should not be too large. The overwintering pond should drain the water half a month before overwintering, remove fish, weeds and debris at the bottom of the pond, and strictly repair the ridges and drains, especially the drainage filter. Conditional units can expose the big pond to crack, and then return water 10-15 cm for disinfection, disinfection can be combined with quicklime and tea meal, the scope of disinfection includes pond bottom, pond ridge, in order to completely kill miscellaneous fish and bacteria, it is best to use fresh river water or well water when returning water. The overwintering pond water does not require the cultivation of fertilizer water, because the fertilizer water quality is not conducive to the management during the overwintering period, which increases the difficulty of management. 5-7 days after disinfection and return water, the fish can be released in the water.

2. Preparation and construction of overwintering materials

The main purpose is to make a shed arch frame, build a row of support frames with wooden piles in the middle of the big pond, then set up a small steel wire on it, fix it with a wooden pile on the edge of the pond, cover it with a thin film, press the steel wire rope on it, and fix the upper and lower steel wire rope with a small iron wire. Cover the film to be flattened to prevent Rain Water from accumulating on the greenhouse when it rains. During the overwintering period, we should often check whether the film has loopholes and take corresponding measures in time.

3. Preparation of overwintering equipment

According to different overwintering methods, the heating, oxygen, sewage and other equipment needed during the overwintering period should be ready before overwintering, such as heaters, boilers, temperature controllers, water pumps, aerators and so on.

Preparation of overwintering fish before entering the pond

1. Fattening before overwintering

A month before overwintering, fish will be hoarded in technical secondary school ponds to strengthen cultivation, promote their fat and strong body, enhance their cold resistance over the winter, make them gradually adapt to the living environment during the overwintering period, and eliminate some weak or injured fish ahead of time.

2. Selection and retention of overwintering fish

There are two kinds of overwintering fish: (1) parent fish: when the parent fish enters the pond, it should be strictly selected according to the requirements of producing fry to ensure that each parent fish meets the requirements. The male and female ratio of parent fish is selected at 3:1 or 4:1, and the male and female are separated into ponds for overwintering, so as to facilitate the operation of cross breeding in the coming year. The remaining quantity is based on the planned amount of fry growth plus 15% Mur20% to ensure the smooth progress of seedling production in the coming year.

(2) Fish species: it is better for overwintering fish species to be 4-6 cm. General fry are required to enter the pond in the same specification when overwintering, which will reduce the utilization rate of overwintering ponds. Too small fish species have poor adaptability, low survival rate and different sizes of overwintering fry in the same pond. The selected fish species should also pay attention to the selection of individuals with strong physique, no injury, no disease, smooth body surface and no frostbite.

Whether it is the selection of parent fish or fish species, the operation must be brisk and meticulous, so as not to damage the fish body, and enter the pond immediately. Fish species should not be concentrated in the net pool for a long time when they are graded and screened. Generally, after hanging water in the net pond for two hours, they can be screened and counted into the pond, the longest time should not be more than five hours, and it is not suitable to carry out high-density long-distance transportation, otherwise it will cause serious injury to the fish body and lead to low survival rate over the winter.

3. Fish body disinfection

The parent fish overwintering, and the fish species have varying degrees of damage in the process of transportation and operation. The fish should be disinfected with drugs before entering the pond. The fish body can be soaked in 2% Mui 3% salt solution (without iodization) for 5-10 minutes before going into the pond. After all fish species enter the pond, 0.3ppm chlorine dioxide can be used for whole pond disinfection to prevent diseases. Within one week after entering the pond, we should pay close attention to the activities of fish species entering the pond, especially if the fish species operated at low water temperature are infected, and take corresponding measures in time. After entering the pond for a week, the condition of the fish species is basically stable, and then enter the overwintering period of management.

Time and density of overwintering fish entering the pond

1. Time to enter the pool

It is appropriate to enter the pond when the water temperature is 18-20 ℃ and end before the first cold snap. Once the water temperature is lower than 16 ℃, the fish caught at the beginning cannot be used as overwintering fish, because the water temperature will cause frostbite and die one after another after entering the pond. When fishing into the pool, it is appropriate to choose stable weather and strong sunshine. Generally, the net is opened after 09:30 and ends before 04:30, so the water temperature is higher for a period of time, which is conducive to operation.

2. Stocking density

The pond density of overwintering fish is determined according to the overwintering environmental conditions, fish size and management level. In the film overwintering pond, static water increases oxygen, generally, parent fish can be released 5-8 kg per cubic meter of water, but because parent fish should be strengthened before breeding in the original pond in the later stage of overwintering, conditional units should reduce the stocking density of parents, generally 500-600 per mu, 500-600 grams per tail. If the seedlings are produced in pairs in the original overwintering greenhouse, the number and weight of female and male parents should also be considered. The stocking density of overwintering fry is 3-4 cm, 10-120000 fry per mu, 4-5 cm, 8-100000 fry per mu, and 70-80 000 fry over 5 cm. Small size seedlings overwintering, because it is smaller, the survival rate is lower, so it should be appropriately increased into the pond, after deducting the survival rate to reach the general overwintering level, after strengthening the cultivation, it can reach the specification of 5-7 cm; and as a large-size seedling, because the survival rate is higher after entering the pool, the density of large-size seedlings should be denser when entering the pool, so it is most appropriate to keep the specification uniform and stable at 5-7 cm.

Feeding and management during overwintering

Tilapia overwintering period is longer, usually from mid-late October to late March of the following year, about half a year. In production, the overwintering is generally divided into three stages of management. the water temperature in the early stage of entering the pool and about to leave the pool is higher, so more materials should be added appropriately to regulate the water quality; if the temperature is low in the middle stage, the feeding should be reduced appropriately to prevent the deterioration of water quality; the management in the late overwintering period is particularly important to strengthen the quantity and quality of feed before leaving the pool to promote the physical recovery and gonadal development of parent fish, so as to ensure the quality of seedlings after coming out of the pool. During the whole period of overwintering, special personnel should be responsible for keeping records, controlling water temperature, regulating water quality, feeding materials, preventing diseases, and so on.

1. Control of water temperature

The water temperature of the overwintering fish should be controlled between 20-25 ℃ within 10 days after entering the pond, which is beneficial to the wound healing of the fish as soon as possible and inhibit the occurrence of water mildew. After the situation is basically stable, the water temperature can be controlled between 18 and 20 ℃. The water temperature must not rise or fall suddenly, nor can it be controlled above 20 ℃ for a long time. Long-term high temperature is not conducive to overwintering management, and it will also increase the input of feed, because the water temperature is high, the vitality of fish is strong, physical exertion is more, and food intake will increase. If you use an ultra-thin film greenhouse, as the sun warms up during the day, the temperature in the pool is sometimes as high as 30 ℃, at this time, you should open part of the film to allow air circulation, control the air temperature in the shed at about 21 ℃, and control the water temperature at 18-19 ℃. In case of sudden weather or cold snap, the film should be covered back in time to prevent sudden cooling.

2. Regulation of water quality

The water quality of the overwintering pond should be kept fresh and the dissolved oxygen content is sufficient. Because of the large area of the overwintering pond, it is difficult to change water, so under normal circumstances, only part of the new water is added. During the overwintering period, some microbial preparations (such as probiotics, aquaculture treasure, etc.) can be used regularly to regulate the water quality and increase the vitality of the water. When the water color becomes thicker, you can change part of the old water and inject new water, but the change of water should not be too much, controlled between 1max 4 and 1max 5. When adding water, the flow should flow straight into the pond, and the outlet must be covered with a filter to prevent weeds from entering or fish swimming out against the current. The flushing time during the day should not exceed four hours, especially in the seedling pond, which should be controlled at about 2-3 hours, so as to prevent the fish fry from consuming too much physical strength for a long time or intensive for a long time to increase fish damage.

3. Oxygenation equipment

As the overwintering culture density of Datang winter shed is generally higher and the water quality is generally more fertile, the overwintering ponds should be equipped with oxygen-increasing equipment. In the low temperature season, due to the low surface water temperature, the fish exposed to the water surface after anoxic floating head, easy to frostbite, easy to grow water mold, resulting in festering and death; in the later stage of overwintering, due to the increase of water temperature and the increase of feed, the water quality of parents became fat in the process of prenatal cultivation, which will cause serious hypoxia and affect cultivation. Therefore, it is very important to increase oxygen during overwintering.

4. Reasonable bait

Tilapia should be properly fed with nutritious concentrate during the overwintering period. Generally adopt the way of feeding with more than two ends and less in the middle, that is, after entering the pool, appropriate feeding should be given for a period of time, the parent fish should be controlled at about 2%, and the fish species should be controlled at about 5%, 6%, once a day, and it would be better to feed all the fish. For the seedling pond, excessive feeding is arranged once or twice a week for some weak seedlings, because they can not compete for feed because of the small amount of feed, and if they can eat it once or twice a week, they will be able to maintain physical exertion and not die of emaciation. Fish seed feed can be powdered or small caliber formula feed, feeding should be evenly fed throughout the pond, so that most fish fry can be eaten, parent fish feed should be made into floating pellets, sedimentation materials should be set up properly, and it is appropriate to eat within 1.5 hours. When you can't finish it, you should remove the residue in time and reduce the amount of feed, so as to prevent the deterioration of the feed from affecting the water quality. During the overwintering period, the quantity and quality of feed are adjusted at any time with the water temperature, water quality and fish intake.

Daily management

1. Pay attention to the change of water temperature

Often measure water and temperature, usually twice a day, and make a good record.

2. persist in patrolling the pond in the morning, in the middle and in the evening.

Check whether the overwintering greenhouse is firm, often observe fish vitality, food intake, monitor water quality, and regularly monitor several indexes such as dissolved oxygen, ammonia chlorine and organic matter in the pond, record them, find problems in time, and take measures to prevent accidents.

3. Pay attention to ventilation and ventilation

In the later stage of overwintering, due to the rise of water temperature, we should pay attention to the ventilation and air exchange of the overwintering shed, and the water temperature is stable, so we can open the shed to cool down and add fresh water. When the water temperature of the overwintering shed is the same as that of the outside world, the preparation work before the pond can be made.

4. Pay attention to disease prevention

In the overwintering season, tilapia is more prone to disease due to the small area of overwintering ponds, high density, relatively poor water quality, low water temperature, inactivity and less food intake. Fish disease mainly adopts the principle of prevention and treatment. During the overwintering period, quicklime is used once every half month, with a dosage of 10-15 kg / mu. After using quicklime for 7-10 days, disinfect with 0.25-0.3ppm chlorine dioxide and use insecticidal drugs once a month. Note that all kinds of drugs should be used separately and alternately. Always check the activity of the fish, find any abnormal situation, and deal with it in a timely manner.