Parent Stock Cultivation and Breeding Techniques in Tilapia Farming

Tilapia breeding does not require artificial hormone injection or flowing-water stimulation; as long as the water temperature remains stable above 20°C, placing mature male and female parent fish into the same breeding pond allows them to breed naturally. When the water temperature is stable at 25-29°C, they can breed once every 30-50 days and produce fry. In the southern regions of China, tilapia can generally produce fry five to six times a year, and under temperature-controlled conditions they can breed year-round.

I. Breeding Pond Conditions 1. Location The breeding pond should be chosen near a water source, with convenient water inlet and drainage, a quiet environment, and convenient transportation; it is best to choose a location near the pond where the parent fish overwinter, in order to reduce injuries caused by transferring the parent fish between ponds. 2. Area and Water Level The area of the breeding pond is generally 2-6 mu; too large an area is not conducive to collecting fry, while too small an area makes water quality difficult to control and water temperature changes more obvious. When the parent fish are first placed in the pond, the water level should be controlled between 1.4-1.5 m. During parent fish breeding, the water level should be reduced to 0.8-1.2 m; during the high-temperature summer period, it may be appropriately deepened to 1.2-1.4 m. 3. Pond Shape and Bottom Substrate The pond shape is best as a rectangle running east-west in length and north-south in width, with shallow water beaches along the edges to facilitate the parent fish digging nests and producing fry. The pond bottom should be flat or slightly pot-shaped, and the bottom substrate is best as loam or sandy loam. There must be no weeds on the shallow water beaches along the pond edges, otherwise it will not be conducive to collecting fry. II. Cleaning and Disinfection of the Breeding Pond Before the parent fish are placed in the pond, the breeding pond must be cleaned and disinfected. During cleaning, the pond water should be drained, wild fish removed, and weeds and debris at the pond bottom cleared, especially weeds within 1.6 m from the pond bottom to the pond edge, and a strict check should be made of whether the pond edges, pond embankments, and inlet and drainage filter nets are firm; it is best to let the pond bottom be exposed to the sun until it cracks. 10-15 days before the parent fish are placed in the pond, refill with 10-20 cm of water, then use chemicals to treat the pond. Commonly used chemicals include tea seed cake, bleaching powder, and quicklime, among which quicklime and tea seed cake have the best effect. The dosage of tea seed cake is 40-50 kg/mu, quicklime 150-200 kg/mu, and bleaching powder 15-20 kg/mu (effective chlorine 30%). After several days of water cultivation and disinfection, use a fine-mesh net to pull through the pond and check whether disinfection inside the pond is complete. After confirming that there are no other wild fish or debris in the breeding pond, refill with water (when filling, the water inlet must be filtered with a fine net, and the fine net must be checked and cleaned frequently), and apply base fertilizer. Apply 300-600 kg of fermented manure per mu or 500-800 kg of green manure, and control the water quality to appear tea-green or yellow-green (if green manure is applied, it should be turned frequently, and after it has completely rotted, the grass residue should be removed; after 7-10 days of disinfection, test the water and release the fish). III. Stocking Parent Fish 1. Selection of Parent Fish The tilapia used as parent stock must be purebred. Within the same population, individuals that grow quickly and are relatively larger should be selected; generally, overwintering fingerlings should be above 250 g, with males slightly larger, keeping the large and removing the small. When selecting, the chosen parent stock should have a high back and thick flesh, complete scales and fins, bright color, clear stripes, no disease or injury, uniform body shape, and external morphology conforming to taxonomic standards. 2. Stocking Time When parent fish are placed into the breeding pond, the water temperature should preferably be stable above 20°C. In Guangdong, pairing and fry production can generally begin in mid-to-late March. Because Hainan has a relatively favorable natural climate, pairing and fry production can be carried out year-round. Stocking parent fish should be done on sunny days, and the full number should be stocked at one time. Before the parent fish enter the pond, the fish body should be disinfected. Soak the parent fish in 3‰-3.5‰ salt water for 5-10 minutes before placing them into the breeding pond. When transporting parent fish, operations should be light and quick to minimize injury to the fish body, shorten the recovery time of the parent fish, and advance fry production. After all parent fish have entered the pond, disinfect with 0.3 ppm chlorine dioxide to prevent wound infection in the parent fish and the occurrence of saprolegniasis. 3. Stocking Density and Male-to-Female Ratio The stocking density of parent fish should be determined according to the oxygen supply capacity of the pond water, pond conditions, and production quantity. In an ambient-temperature pond, with one 1.5-2.2 kW aerator for 2000 cubic meters (about 3 mu) of water, the stocking density can reach 1500-2000 fish/mu, with a size of 250-300 g. Under conditions without aeration equipment, 600-800 parent fish of 300-500 g can be stocked per mu. In a still-water heat-preserving and oxygen-supplementing pond covered with plastic film in the morning and evening, the stocking density of parent fish is 1000-1200 fish, with a size of 250-300 g. When stocking, the male-to-female ratio must be properly controlled. According to our institute's production experience over several years, a male-to-female ratio of 2.5:1-4:1 gives a relatively ideal fry yield, because when too many males are stocked, if there is insufficient feed they will consume large numbers of fry, seriously affecting the fry yield. Cultivation and Management After a long overwintering period, parent fish are relatively weak in constitution and poor in gonadal development, so cultivation must be strengthened. Strengthen cultivation using an adult fish rearing method combining fertilization and feeding. Feeding and fertilization should depend on the weather and the feeding situation of the parent fish. The general daily feeding amount is 3%-4% of the total weight of the parent fish in the pond. To promote the gonads of the parent fish to develop and mature as quickly as possible, feeding should combine formulated feed and green feed, with variety, so that nutrition is comprehensive. The protein content of the formulated feed for parent fish should be above 35%. Commonly used feeds include soybean meal, fish meal, corn meal, peanut meal, and yellow powder. As feed for parent fish, it is best to purchase raw materials and make them into pellet feed oneself. After the parent fish enter the pond, persist in inspecting the pond in the morning, at noon, and in the evening, promptly remove frog eggs from the pond and kill predators, and especially strengthen water quality management. When the water color is too dense or shows a dark brown color, effective measures should be taken promptly, such as exchanging part of the water for new water or splashing lime, to prevent losses caused by hypoxia and pond turnover due to water quality deterioration. Persist in regular disinfection of the breeding pond and regulation of water quality. Generally, apply quicklime once every half month, with the dosage controlled at 10-15 kg per mu. Regularly apply some microbial preparations to change the pond's microbial community and improve the aquatic environment. IV. Parent Fish Fry Production 1. Fry Production Water Temperature After parent fish are stocked, when the water temperature rises to 22°C, the cultivated mature parent fish begin to become sexually active and spawn. The hatching of fertilized eggs and the nurturing of fry take place inside the female fish's oral cavity. At a water temperature of 25°C, they hatch and emerge from the membrane in about 5-6 days; at 28-30°C, they hatch and emerge from the membrane in 4-5 days. From the parent fish becoming sexually active and spawning to the fry leaving the mother's body to live independently, the whole process takes about 10-15 days. Therefore, after the parent fish have been stocked for 10 days, persist in carefully observing around the pond every day to see whether there is fry activity, so as to collect fry in time and increase the fry collection rate. 2. Fry Collection Fry collection is generally carried out in the morning or evening. A relatively good method is to use hand nets or small trawl nets to catch along the pond perimeter, lifting the net once every 3-4 m, and placing the young fry into a net cage for temporary holding. Repeat this process, and collect 4-5 times each day, trying to collect all the young fry as much as possible each day. When collecting fry, movements should be light and quick. After collecting a certain quantity, count them and move the young fry to the nursery pond, transferring them to the fry cultivation stage. Because tilapia have the habit of cannibalism at the young fry stage, fry with a body length of 1.5 cm can already swallow young fry that have just left the mother's body. In production, fry collection can be combined with fry catching. When catching fry, use a fine-mesh net, and the sinkers on the bottom line should not be too heavy, so that the parent fish can escape from under the net. Several issues that must be noted: 1. Water Temperature Before parent fish are moved from the overwintering pond to the breeding pond, the overwintering pond should be cooled, waiting until the water temperature is level with the outside, and feed should be stopped and new water added 3 days before leaving the pond. When transferring between ponds, operations must be careful to reduce injury to the fish body, because the water temperature during this period is generally not high, and wounds on parent fish are highly prone to saprolegniasis. When moving ponds, in addition to choosing clear weather, the fish must be disinfected before being placed into the breeding pond. 2. Water Quality The amount of fry produced by parent fish depends greatly on water quality, which is a very key link. Water quality cannot be too fertile or too lean. If too fertile, parent fish are highly prone to hypoxia and floating at the surface; if too lean, it is not conducive to cultivating the parent stock and the first feed for the young fry. Regulate water quality well, use quicklime regularly, frequently replace part of the old water and inject new water during the high-temperature season, and it is recommended to use some microbial preparations to improve water quality and increase dissolved oxygen. 3. Feed Another key link in the amount of fry produced by parent fish is feed. As feed for parent fish, it must achieve the quality for strengthened cultivation, and the various components contained in the feed must be very clear. Only when parent fish absorb sufficient protein and energy can the interval between fry production be shortened, the number of fry production times be increased, and the fry emergence rate be improved. 4. Separation of Males and Females During the high-temperature summer period, tilapia show phenomena such as stopping fry production or reducing fry production, and the young fry are extremely difficult to collect. At this time, the parent fish can be separated by sex and cultivated in isolation in separate ponds. When the water temperature drops below 30°C, pair them again for fry production. The purpose of doing this is to be able to collect a relatively concentrated batch of young fry, which is beneficial for fry cultivation and overwintering.