In the breeding practice of Nile tilapia, due to its early gonad maturation and short reproductive cycle, population density is often increased due to frequent breeding, which results in the miniaturization of individuals, which seriously affects the improvement of fish production and reduces the quality of commodities. This article refers to Japan's Nile tilapia over-breeding control technology, summarizing the following experience in order to provide guidance for farmers.
Japan used the naked eye to select mono-herds to solve this problem, and later successfully fed androgen to produce mono- and male seedlings. Now it is basically an all-male seed obtained from cross-breeding. Other methods are also used to control reproduction. The general situation is as follows:
1 Control of Breeding by Breeding Methods Only breeding cages, running water and artificial water tanks can control breeding. The use of buoyant cages for the culture of tilapia can inhibit spawning behavior and avoid overpopulation. It also prevents the broodstock from causing growth arrest due to oral hatching. In stream aquaculture, increasing the flow rate to reduce the chance of fertilization of the eggs can achieve the purpose of controlling reproduction. Experiments have shown that when the flow rate is 20cm/s, the oviposition behavior of fish can be destroyed, but the normal growth is affected. When the flow rate is 10cm/s, the purpose of controlling breeding cannot be achieved. Only when the flow rate is around 15 cm/s, both the purpose of controlling reproduction and the growth and plumpness of the fish are still in good condition.
2 Use high-density breeding to control propagation of Nile tilapia reproduction by the impact of stocking density. Experiments have shown that, as the stocking density increases, the catch volume rises linearly, and the percentage of fish caught by adult fish is reduced. When the stocking density per unit area reaches 3kg/m2, the proportion of fry in adult fish is almost zero. This high-density cultivation prevents the normal spawning hatching behavior from being disturbed by other fish in the breeding ground. However, due to factors such as lack of oxygen and deterioration of water quality, it is not possible to stock 3 kg of fish per square meter in a still pool.
3 Male hormone production and monoandrogen production is generally 17a-methyl testosterone (MT). This hormone is relatively cheap, easy to obtain, and most importantly, it can be absorbed in vivo and has a long effective time. Because this fish is a food fish, it is very important to master this concentration. The oral tests of Nile tilapia with MT were formulated into 50ug/g and 100ug/g feeds, respectively, and 100% male seedlings were obtained. Taking into account the degree of feeding of fry, it is considered that using 100ug/g concentration of feed is good. Tests have shown that the male fry rate of full-length 02.2-14.6mm is 93%-98%; the male fry 13.5-20.2 mm is 70%; only the full length is 8.5-12. .0mm, with an average of 10.5mm of fry, can receive 100% of all-male fry about 30 days after feeding the bait.
4 The use of interspecies hybrids in male and female seedlings is based on the technique of putting Olja tilapia (male) and Nile tilapia (female) into the spawning pond at a ratio of 1:2 to 1:5 and then casting. Feed horns or compound feed. Every two months, the fry in the broodstock is taken from stock or sold.
5 Research on polyculture with predators is not much research in this area. Some people in the Nile tilapia pool were mixed with copper-spotted sunfish and carp. The results showed that the effect of the polyculture of 10% of carp was not significant, while the effect of the polyculture of 10% of the copper sunfish was significant. The number of breeding tilapia seedlings was reduced by nearly half, and the fry growth was more than 3 times faster, which not only improved Tilapia yields and exchanges unnecessary seed for the production of predatory fish.
6 The naked fish of choice for the feeding of single sex fish are generally anesthetized with anesthetic drugs and separated by naked eyes. Use 50-60g fry. As a result of the rearing, single females grow slower than single males but grow faster than males and females. In addition, there are people who propose to transform the bottom structure of the fish pond so that the fish can not dig a hole and spawn eggs to achieve the purpose of controlling the breeding.
Japan used the naked eye to select mono-herds to solve this problem, and later successfully fed androgen to produce mono- and male seedlings. Now it is basically an all-male seed obtained from cross-breeding. Other methods are also used to control reproduction. The general situation is as follows:
1 Control of Breeding by Breeding Methods Only breeding cages, running water and artificial water tanks can control breeding. The use of buoyant cages for the culture of tilapia can inhibit spawning behavior and avoid overpopulation. It also prevents the broodstock from causing growth arrest due to oral hatching. In stream aquaculture, increasing the flow rate to reduce the chance of fertilization of the eggs can achieve the purpose of controlling reproduction. Experiments have shown that when the flow rate is 20cm/s, the oviposition behavior of fish can be destroyed, but the normal growth is affected. When the flow rate is 10cm/s, the purpose of controlling breeding cannot be achieved. Only when the flow rate is around 15 cm/s, both the purpose of controlling reproduction and the growth and plumpness of the fish are still in good condition.
2 Use high-density breeding to control propagation of Nile tilapia reproduction by the impact of stocking density. Experiments have shown that, as the stocking density increases, the catch volume rises linearly, and the percentage of fish caught by adult fish is reduced. When the stocking density per unit area reaches 3kg/m2, the proportion of fry in adult fish is almost zero. This high-density cultivation prevents the normal spawning hatching behavior from being disturbed by other fish in the breeding ground. However, due to factors such as lack of oxygen and deterioration of water quality, it is not possible to stock 3 kg of fish per square meter in a still pool.
3 Male hormone production and monoandrogen production is generally 17a-methyl testosterone (MT). This hormone is relatively cheap, easy to obtain, and most importantly, it can be absorbed in vivo and has a long effective time. Because this fish is a food fish, it is very important to master this concentration. The oral tests of Nile tilapia with MT were formulated into 50ug/g and 100ug/g feeds, respectively, and 100% male seedlings were obtained. Taking into account the degree of feeding of fry, it is considered that using 100ug/g concentration of feed is good. Tests have shown that the male fry rate of full-length 02.2-14.6mm is 93%-98%; the male fry 13.5-20.2 mm is 70%; only the full length is 8.5-12. .0mm, with an average of 10.5mm of fry, can receive 100% of all-male fry about 30 days after feeding the bait.
4 The use of interspecies hybrids in male and female seedlings is based on the technique of putting Olja tilapia (male) and Nile tilapia (female) into the spawning pond at a ratio of 1:2 to 1:5 and then casting. Feed horns or compound feed. Every two months, the fry in the broodstock is taken from stock or sold.
5 Research on polyculture with predators is not much research in this area. Some people in the Nile tilapia pool were mixed with copper-spotted sunfish and carp. The results showed that the effect of the polyculture of 10% of carp was not significant, while the effect of the polyculture of 10% of the copper sunfish was significant. The number of breeding tilapia seedlings was reduced by nearly half, and the fry growth was more than 3 times faster, which not only improved Tilapia yields and exchanges unnecessary seed for the production of predatory fish.
6 The naked fish of choice for the feeding of single sex fish are generally anesthetized with anesthetic drugs and separated by naked eyes. Use 50-60g fry. As a result of the rearing, single females grow slower than single males but grow faster than males and females. In addition, there are people who propose to transform the bottom structure of the fish pond so that the fish can not dig a hole and spawn eggs to achieve the purpose of controlling the breeding.