Detailed Explanation of the Methods and Key Technical Points for Two-Crop Continuous Tilapia Farming
Two-crop continuous tilapia farming model: large-size tilapia fry are graded and pre-grown, and in the grow-out pond a certain number of filter-feeding silver carp and bighead carp, as well as herbivorous grass carp and carnivorous black carp, are stocked together and cultured with pure feed. After the tilapia reach market size, they are caught and sold; whether the companion cultured fish are sold depends on their size. Without draining the pond, the second crop of large-size tilapia fingerlings is immediately stocked, and after the tilapia are cultured to market size and sold, the pond is drained. What has been described above is the two-crop continuous tilapia farming technique, a farming model summarized from the successful experience of tilapia farmers in Gaozhou, Maoming, in recent years in farming GIFT tilapia; the pond is cleared only once after two crops of tilapia are cultured.
This farming model makes full use of the pond culture space, saves farming time, allows rapid recovery of funds, produces products that meet healthy aquaculture standards for export, and can increase the economic benefits of polycultured silver carp, bighead carp and other companion fish, relatively reducing the pond rent cost for tilapia farming and increasing the tilapia yield per unit area. It is the preferred farming model of pure-feed tilapia farmers in Gaozhou, Maoming, and has local characteristics. Generally, where conditions such as a climate allowing tilapia to overwinter naturally and professional fishing teams are available, this farming model can be used and can generate very good economic benefits. This farming model is introduced as follows:
I. Prerequisites for Two-Crop Continuous Farming
1. Grow-out pond
The grow-out pond does not need to be very regular; ponds or small hill ponds with silt below 20 cm, an area of 5-40 mu, a water depth of 1.5-4 m, a flat bottom and easy harvesting are all acceptable. Generally, 5-10 mu of water surface should be equipped with 2-3 kW of aeration equipment. The bottom conditions of the grow-out pond, such as silt depth and whether the bottom is flat, have a great influence on the tilapia harvest rate. If the pond bottom is uneven with pits, it is difficult to achieve a high harvest rate, and a large number of first-crop tilapia will be left behind, making it unsuitable for two-crop continuous tilapia farming.
2. Selection of tilapia fry
The tilapia fry can be GIFT tilapia or hybrid tilapia, but they are required to have fast growth, a high male ratio and a high harvest rate; the most suitable for two-crop continuous farming is GIFT tilapia. To ensure the quality of tilapia fry, farmers had better choose fry from tilapia hatcheries with a good reputation.
3. Graded pre-growing to cultivate large-size tilapia fry
Graded pre-growing in tilapia farming can make full use of the culture water space, save pond rent, and also make feeding management easier. Two-crop farming generally involves one to three grades of pre-growing, raising 1.5-3 cm tilapia fry to large-size tilapia fingerlings of 100-200 g each. The area ratio of fry rearing ponds to grow-out ponds is 1:3-1:8. Large-size fingerlings are generally reared 2-4 months before stocking in the grow-out pond, thereby ensuring a normal supply of large-size fingerlings for grow-out farming. The pre-growing stocking density depends on the fingerling size to be cultivated, the size of the rearing pond and the rearing conditions. Generally, the stocking density is 6000-15000 fish/mu, and the rearing method is the same as general tilapia fry rearing. It is best to rear the fry in fertilized water to ensure that the small fry have enough first food after being stocked in the pond and to increase the survival rate of the fry. Farmers who lack or do not have fry rearing ponds can also directly purchase large-size tilapia fingerlings for grow-out farming.
4. Pure-feed grow-out farming method
The two-crop continuous farming model is suitable for pure-feed tilapia farming. Other integrated farming methods (using poultry and livestock manure for farming), because poultry, livestock and fish produce a large amount of excrement, easily cause water quality deterioration, slow tilapia growth, and an excessively long culture cycle per crop, and produce too many self-bred small tilapia, are not suitable for the two-crop continuous tilapia farming model.
II. Preparatory Work Before Stocking
Seven days before stocking the first crop, use 80-100 kg/mu of quicklime for dry pond clearing to ensure that all tilapia or other fish in the pond die. Three days later, filter water through a 60-mesh mesh bag to fill the pond to more than 1 m. When the water pH is below 8.6, large-size fingerlings can be stocked; for grow-out farming, there is no need to fertilize the water before stocking the fingerlings.
III. Fry Stocking
The stocking density in tilapia grow-out ponds depends on the pond conditions and generally should not be too dense. In the Maoming area, the general stocking density for this farming model is 1000-1800 tilapia/mu, 20-50 bighead carp/mu, 20-45 silver carp/mu, 5-20 grass carp/mu, and 3-5 black carp/mu (if bighead carp and silver carp are to be harvested after only one crop, fingerlings larger than 500 g each need to be stocked, and the number should also be controlled below 20 per mu to reach a relatively large market size).
IV. Feeding Management
Feeding management is an important part of tilapia farming and has an important influence on saving costs and reducing disease occurrence. The feeding management of two-crop continuous tilapia farming in the Maoming area is as follows:
1. Feeding method
Whether floating feed or sinking feed is used, a feeder is suitable; feeders can save labor and also achieve the effect of uniform feeding by the tilapia. A pond of 5-15 mu is equipped with one feeder, and a pond of 15-40 mu is equipped with two or more feeders, so that the feeding coverage area is large enough to ensure uniform feeding by the tilapia. In this way, the fish sizes will not become polarized, and the fish harvested from the pond will be relatively uniform in size.
2. Feeding frequency and feeding amount
Generally, the feeding frequency is twice a day. The daily feeding times are 8:00-9:00 in the morning and 15:00-17:00 in the afternoon. The feeding amount accounts for 0.8-6% of fish body weight and generally depends on the weather, fish size, water quality, water temperature, feeding situation and fish price trend. Under conditions of sufficient sunlight, adequate wind, a good wind direction, suitable water temperature and good water quality, feed can be given fully; under low pressure, low temperature, cloudy and rainy days, before a typhoon arrives, or when water quality is poor, feed less or do not feed. In short, feeding should ensure the nutritional needs of the cultured fish without wasting feed and causing water pollution.
Because different tilapia varieties have different feeding intensities, at a water temperature of 16 degrees C, GIFT tilapia still feed normally, but the feeding rhythm of hybrid tilapia is very low, because at low temperatures the digestibility of tilapia is not high, and farmers should control the feeding amount according to the actual situation. Based on many years of farming experience, tilapia farmers in Gaozhou feed tilapia over 200 g 8-12 g of feed per day under normal weather, water temperature and water quality conditions.
3. Feed selection
Grow-out farming feed should generally be comprehensive in nutrition and fresh. The feed of large tilapia farmers in the Maoming area is generally self-formulated and processed feed to ensure quality.
V. Management and Disease Control
1. Water quality management
Turn on the aerator appropriately to keep the dissolved oxygen in the water body sufficient. Generally, under good weather conditions, turn on the aerator for 2-4 hours at noon and in the early morning each day; under poor weather or poor water quality conditions, increase the operating time, turning it on 4-10 hours per day. Keep dissolved oxygen greater than 4 mg/L for 24 hours. Change (add) water by 10-40 cm each month to keep the pond water “fertile, alive, tender and refreshing.” In hot summer or cold winter, it is appropriate to keep the water depth at 2-3 m. Once a month, splash limewater at 10-15 kg of quicklime per mu. Use EM bacteria, bottom substrate regulators, etc. according to the product instructions.
2. Control of second-generation tilapia fry
Long-term tilapia farming will lead to self-breeding, and many small fry cause the problem of wasted feed. In the middle of the first crop, 30-40 snakehead fish of 30 g each can be stocked per mu to solve the problem of too many self-bred small tilapia and ensure the success of the second crop of tilapia farming.
3. Fish disease control
The tilapia farming density in the Maoming area is not high, and diseases rarely occur in the two-crop continuous farming model. If pond clearing and disinfection before stocking, water quality regulation and feeding management are done well, major diseases generally do not occur. In recent years, tilapia streptococcosis has broken out frequently. Enrofloxacin can be mixed into feed and fed: at a dosage of 10-20 mg per kg of fish body weight per day, once a day, for 5 consecutive days, with a water temperature above 18 degrees C, and a withdrawal period of 10 days.
VI. Harvesting and Marketing of the First Crop of Tilapia
When the tilapia have been cultured to market size, appropriately lower the water level (1-1.5 m) for the first harvest and marketing, then lower the water level again (0.5 m) to catch as many tilapia as possible for marketing. Generally, the tilapia harvest rate reaches more than 90%. If other companion fish such as silver carp and bighead carp do not reach the required market size, they continue to be cultured in the original pond, and snakehead fish continue to be cultured. Harvesting and marketing the first crop of tilapia takes at most only four days, greatly saving farming time.
VII. Stocking and Farming Management of the Second Crop of Tilapia
After the first crop of tilapia is marketed, water can be let into the pond that same day. When the water level reaches more than 0.7 m, large-size tilapia can be stocked. The stocking density is similar to that of the previous crop or somewhat lower. Whether to stock companion silver carp and bighead carp depends on the situation; if the silver carp and bighead carp from the previous crop have not been marketed, there is no need to stock them again. Tilapia farming management is the same as conventional practice.