Gibel fish and largemouth bass pollution-free aquaculture focus, difficulties and examples

Author: Xu Zaikuan, Shi Tinghua / Country: Mainland China
Publisher:
Publish Date: 2005-05-01
Features: [Excerpt:] 2. Polyculture in Ponds (1) Mixed Culture of Parent Fish and Adult Fish in Ponds
In ponds where domestic fish and wildfish are abundant, a water surface area of 1,000 square meters can yield 15 to 30 kilograms of wildfish. These wildfish compete with domestic fish for oxygen, food, and space, and their low economic value also hinders the increase in the yield of cultured fish. However, these wildfish are suitable as feed for Mandarin fish. Therefore, culturing a small number of Mandarin fish fry in fish ponds can suppress the growth of wildfish, converting low-value fish into high-value fish. In ponds for domestic fish parent fish, Mandarin fish not only feed on wildfish but also promote the development of the gonads of domestic fish parent fish. The characteristic of pond polyculture is that without increasing or only slightly supplementing feed fish, Mandarin fish can be raised for 4 to 5 months, yielding 10 to 15 kilograms of commercial Mandarin fish weighing 950 to 500 grams per tail per acre. The size of the Mandarin fish fry for polyculture should be more than double that of the main cultured fish. The number of Mandarin fish fry for polyculture can be determined based on the polyculture size, the supply of wildfish and feed fish, and the fish-carrying capacity of the pond. Generally, 300 to 750 summer fingerlings of Mandarin fish are polycultured per acre. Small rivers and streams have better water quality and dissolved oxygen than ponds, so the polyculture amount can be increased. Additionally, lotus ponds and small external lakes can also be polycultured. There are two types of polyculture species combinations: one is with Mandarin fish as the main species, and the other is with Mandarin fish as a supplementary species. Mandarin fish can be polycultured in ponds for parent fish of silver carp and bighead carp or in commercial fish ponds. Generally, 15 to 30 fingerlings of Mandarin fish weighing less than 25 grams or 40 to 60 fingerlings with a body length of about 3 cm are stocked per 1,000 square meters of water surface. Since no additional feed fish are added, it is not advisable to stock too many to avoid the situation where Mandarin fish do not reach market size by the end of the year. (2) Mixed Culture in Fish Fry Ponds
In fish fry ponds, fish fry become the feed for Mandarin fish. However, through the selective feeding of Mandarin fish, strong and large-sized fish fry can be obtained in the end. P1271) Stocking of feed fish. The yield of feed fish directly affects the yield of Mandarin fish and the economic benefits of the pond. Due to high density, feed fish grow slower than Mandarin fish, ensuring their smooth utilization by Mandarin fish. However, if feed fish grow too slowly and are of small size with low yield, the amount of feed for Mandarin fish will be insufficient, resulting in low yield of Mandarin fish. Therefore, the cultivation of feed fish must be strengthened, and the amount and frequency of feed should be appropriately increased to promote their rapid growth. Through the dual regulation of inhibitory effects at high density and enhanced cultivation, the body length of feed fish is adjusted to about 50% of the body length of Mandarin fish. Based on the fertility of the pond and the supply capacity of domestic fish feed, determine the stocking density of domestic fish fry. Generally, it is 2 million tails per acre. The survival rate is estimated at 80%. 2) Stocking amount of Mandarin fish fry. Generally, the daily ration of Mandarin fish is calculated as 10 tails of feed fish per tail of Mandarin fish. Therefore, 400 to 600 tails of Mandarin fish fry per acre can be stocked. 3) Timely separation and harvesting of large-sized Mandarin fish. After a period of cultivation, there is significant growth differentiation. If not separated, large-sized Mandarin fish will grow even faster by consuming small-sized fish fry, leading to greater differences in individual sizes. Meanwhile, as the number of feed fish decreases rapidly and their density decreases, their growth accelerates, which will affect the feeding and growth of small-sized Mandarin fish. Therefore, during the cultivation process, it is necessary to frequently check the feeding and growth of Mandarin fish. Large individuals should be sold or transferred to other ponds for cultivation to improve the utilization rate of domestic fish fry. 4) Results of mixed culture. Generally, high-quality and large-sized fish fry (silver carp and bighead carp) weighing 30 to 400 kilograms (10 to 15 tails per kilogram) can be harvested. The yield of Mandarin fish is 100 to 200 kilograms (250 to 500 grams per tail). (3) Points to Note in Pond Polyculture 1) Mandarin fish parent fish can swallow 2-year-old domestic fish fry or adult fish. Generally, they are not stocked in adult fish ponds but can be polycultured with silver carp and bighead carp parent fish ponds or raised as a single species. 2) To avoid affecting the yield of other economic fish, only fish of 2 years or older and larger sizes can be polycultured with Mandarin fish. 3) Control the stocking amount of Mandarin fish and avoid stocking other carnivorous predatory fish at the same time, otherwise it may lead to the consequence of insufficient feed fish and the swallowing of cultured fish. 4) Polyculturing Mandarin fish in ponds dominated by grass carp and black carp yields better results.