Detailed Explanation of the Key Points of Mudskipper (Boleophthalmus pectinirostris) Breeding Technology in Earthen Ponds
The mudskipper (Boleophthalmus pectinirostris) is a warm-water fish with broad temperature and salinity tolerance. Its flesh is delicious and has nourishing and strengthening effects, and it is deeply loved by coastal people in Zhejiang, Fujian, Guangdong, Taiwan, China and other provinces as well as by Japanese consumers, so market demand is very large and the price is high. Because mudskipper resources are gradually declining, in the 1980s, mudskipper aquaculture began along the southeast coast of China. Because the mudskipper has a short food chain, few fish diseases, live fish tolerate long-distance transport, and the breeding technology is easy to master, the breeding cost is low and the economic benefits of breeding are high, mudskipper aquaculture has developed rapidly, and at present the aquaculture area of mudskipper in Fujian Province has reached more than 50,000 mu. However, to date it still relies on natural seedlings. In order to protect natural seedling resources and promote the sustainable development of the mudskipper aquaculture industry, there is an urgent need to carry out research on mudskipper breeding in earthen ponds. In 2003, Xiamen University, the Fisheries Technology Extension Station of Xiapu County, Fujian Province and other units undertook the Fujian Provincial major science and technology project "Research on Productive Seedling Technology and Standardized Aquaculture of Mudskipper." The project passed appraisal in January 2006, among which: outdoor earthen ponds produced a total of 1.254 million mudskipper fry with a total length of 1.6-3.1 cm in 2004 and 2005, and the earthen pond breeding technology is at the international leading level. The key points of mudskipper earthen pond breeding technology are introduced as follows:
I. Seedling facilities
1. The bottom substrate of the seedling pond is silty clay. The area of each pond is preferably about 1 mu, the pond depth is 0.8-1.3 m, the pond embankment is firm and does not leak, and an inlet and drainage system is provided. The pond is surrounded with 80-mesh sieve silk mesh. Supports are set up in the pond so that a shade net can be covered above the pond. About 1 air stone is set every 10 sq m.
2. Reservoir, sand filter pond and bait organism culture pond. A reservoir is built in the high tide zone. For a seedling farm with a total seedling pond area of 5 mu, 1 reservoir is built, with an area of 500 sq m and a pond depth of 2 m. Seawater is taken in from the sluice gate at high tide, and water is stored by pumping at low tide. One sand filter pond is built, with an area of 40 sq m. After seawater is filtered, it enters the seedling pond and bait organism culture pond through 120-mesh sieve silk mesh. For convenient extension, directly pumping seawater and filtering it through a double-layer 120-mesh sieve silk net cage is also acceptable. Small pot-shaped cement ponds (1-2 sq m) are built to hatch bivalve trochophore larvae, and 1-2 earthen ponds are reserved for applying EM (effective microorganisms preparation), compound fertilizer and fish slurry to culture bait organisms such as rotifers and copepods.
II. Pond clearing, pest elimination and benthic diatom culture. 45 d before stocking broodfish, clear the pond with water, applying 100 kg of quicklime or 10 kg of bleaching powder per mu to kill harmful organisms. After washing the pond, dry the pond for 5-7 d, feed 20 kg of rice bran per mu, add water to 5-10 cm, and apply 5-10 ppm of compound fertilizer to culture benthic diatoms.
III. Broodfish stocking and cultivation. 30 d before spawning, stock broodfish (generally in early March of the lunar calendar). Select 2-year-old individuals from pond culture and/or intertidal mudflats as broodfish. The sex ratio of female to male fish is 1:1. Male and female broodfish can be identified by the appearance of the genital papilla. The female genital papilla is large and round-blunt, appearing red and swollen, while the male genital papilla is narrow and small, appearing pointed and elongated. The stocking density is 50 kg per mu, and the broodfish size is about 25 g per fish. Before stocking, broodfish are disinfected with fresh water and povidone-iodine. During broodfish cultivation, the water level is maintained at 5-10 cm, and the management of benthic diatom culture is strengthened to ensure the nutritional requirements of the broodfish.
IV. Natural spawning and hatching of broodfish. During the reproductive period, broodfish in the pond spawn 2 batches each month. The spawning dates are from neap tide to near spring tide, that is, from the 8th to the 13th and from the 23rd to the 28th of each lunar month, and each spawning period is about 6 d. Before spawning, raise the pond water level to more than 0.7 m. Female and male broodfish freely pair and enter burrows, and spawn in the spawning chamber of the burrow. Fertilized eggs adhere to the top and surrounding walls of the spawning chamber, and larvae hatch after 5-6 d. After hatching, larvae leave the burrow at 1-2 days of age.
V. Cultivation of larvae, juveniles and young fish. Larvae and juveniles are cultivated in the original pond. Chlorella and Brachionus plicatilis are introduced into the seedling pond in advance. Apply 10 ppm EM, 2-3 ppm compound fertilizer, 1-2 ppm Huolidan (a compound diatom nutrient preparation produced by Xiamen Qiangsheng Technology Co., Ltd.) and 2-4 ppm fish slurry to culture bait organisms such as copepods in the pond. When bait in the pond water is insufficient, rotifers, copepods and other bait must be promptly pumped from the bait organism culture pond. Artificially hatched bivalve trochophore larvae can also be added, and sea mud slurry (soft mud rich in diatoms and organic debris) can be evenly sprayed into the pond with a high-pressure spray gun. Egg yolk and shrimp flakes can also be supplemented. Larvae begin to feed at 2-3 d after hatching. The series of baits for larvae, juveniles and early young fish are particulate organic debris, Tintinnopsis, polychaetes and bivalve trochophore larvae, copepod nauplii, copepod juveniles and adults, and benthic diatoms. The bait organism species and individual sizes in the seedling pond are diverse, basically meeting the needs of larvae, juveniles and young fish at different developmental stages and for different individuals. During seedling cultivation, the water level is gradually raised. When the water level in the seedling pond reaches the upper limit, begin appropriate water exchange, and introduce fresh water to adjust the pond water salinity to 15-20. During seedling cultivation, the water temperature should not exceed 32°C, and the water temperature can be controlled by covering the earthen pond with a shade net and increasing the water level. Different batches of larvae, juveniles and young fish cultivated in the same pond do not show cannibalism. Frequently check the pond water color and monitor changes in dissolved oxygen content in the pond water. When the water color is yellow-green, the water quality is relatively good. If eutrophication of the pond water causes dissolved oxygen supersaturation or dissolved oxygen that is too low, as well as uneven light causing fry to cluster, promptly turn on the aerator. Dissolved oxygen supersaturation can cause larval swim bladder expansion and death. During fry cultivation, because the water level is high, the reproduction of benthic diatoms is affected. One foam board of about 4 sq m can be set in each pond, and artificial compound feed and surface sea mud (soft mud rich in diatoms and organic debris) are fed for broodfish to consume.
VI. Fry harvesting
Early young fish (34 days of age after hatching) rely on their pelvic fins to attach to the mesh around the pond. At this time, fry can be harvested in batches with hand nets and temporarily cultured in earthen ponds rich in benthic diatoms. When harvesting the last batch of fry, the pond water can be drained, and harvested with trampling nets, set nets and lift nets.