Detailed Explanation of Key Points in Artificial Breeding Technology for the Hucho taimen
The Hucho taimen belongs to the genus Hucho in the family Salmonidae; this genus has a small mouth. The posterior extension of the maxilla does not reach the posterior margin of the eye. One species is found in China. It is a cold-water fish, inhabiting mountain streams with relatively low water temperatures and clear water, and overwintering in deep pools of tributaries or in large rivers. Females mature at 4-6 years of age, while males mature earlier than females. When the ice thaws in early spring, they migrate upstream to spawn. Spawning grounds are generally located in rapid currents below deep pools (with a substrate of sand and gravel, water temperature 8-12°C). The eggs are demersal, with an egg diameter of 3.7-4.2 mm. It is a carnivorous fish and also feeds on the eggs of chum salmon during their spawning season. Its flesh is tender and has a high fat content, making it suitable as a new aquaculture species. Its natural resources have become depleted.
The Growth Environment of the Hucho taimen
The Hucho taimen is a relict species that migrated southward from the north during the glacial period, belonging to cold-water piedmont fishes. It lives in mountain streams at altitudes of 900-2300 m in the Qinling region, where the currents are swift, the water is clear, the bottom is mostly large gravel, and the water is rich in dissolved oxygen, with the annual water temperature not exceeding 20°C. In late autumn, it overwinters in deep pools or deep channels of river courses. Except during flood periods, it is rarely seen in the main streams of plains.
It actively feeds throughout the four seasons. It mainly feeds on invertebrates, small fish, etc., and also preys on frogs and small rodents. It is extremely voracious; the food in its stomach can account for about 10% of its own body weight, and it can even prey on fish half its own body length. Its appetite is strongest in the morning and evening each day, and at other times it mostly lurks in shaded bottom areas along both banks of streams. After spawning, its appetite is especially strong. It generally overwinters in deep water areas of rivers.
In its natural state, the Hucho taimen prefers to inhabit flowing water with relatively low water temperatures and fresh water quality, and overwinters in deep pools of river tributaries or in large rivers. It is a carnivorous fish, mainly feeding on invertebrates, small fish, etc., and also preying on frogs and small rodents. The Hucho taimen first reaches sexual maturity at 3—5 years of age, and sexually mature individuals spawn each year in February—March when the water temperature reaches 8—12°C; the eggs are demersal and light yellow. The larvae like to hide among gravel crevices and do not often move about; they usually feed on small fish, aquatic insects, small animals living along the water's edge, and plants.
The Economic Value of Hucho taimen Aquaculture
The Hucho taimen has tender flesh and a high fat content, and can serve as a new aquaculture species.
The Hucho taimen is a national second-class protected aquatic wildlife species and has important academic research value in ichthyology and zoogeography. Before 1980, its numbers were relatively high, but due to human economic activities, overfishing, and other reasons, the Hucho taimen has been greatly reduced and is on the verge of extinction.
The Qinling Hucho taimen grows quickly, has tender flesh, no intermuscular bones, and a delicious taste; it has the functions of preventing blood clots and accelerating wound healing, and is also called brain gold; it has very high nutritional value. It was already a tribute to the imperial court in the Song Dynasty. It is superior to the “rainbow trout” produced in California, USA, and in 1981 it was listed as one of the precious resources of the Dingxi region.
The Breeding Technology for the Hucho taimen
1. Larval rearing. The rearing container is a fiberglass parallel trough (40 cm×30 cm×20 cm), with flow-through aquaculture, an inflow rate of 18-20 L/min, and a 100-watt fluorescent lamp set 60 cm above the water surface for illumination. The stocking density is 10,000 individuals per trough. Newly hatched Hucho taimen larvae have a total length of 14-16 mm.
2. Juvenile rearing. The juvenile fish pond has dimensions of 10 m long, 2 m wide, and 30 cm deep. When the yolk sac of the Hucho taimen larvae is 2/3 absorbed, they gradually float up and swim in the water. In the parallel troughs, the juvenile stocking density is 6,000 individuals/sq m, and in the juvenile fish pond the juvenile stocking density is 3,000 individuals/sq m. When the floating rate of the juveniles exceeds 50%, start feeding them opening feed; artificial compound feed is suitable as the opening feed. A juvenile artificial compound feed with a crude protein content of 45% may be selected, but the fat content should be above 12%. The feed particle size is 0.3-0.5 mm.
3. Fingerling rearing. Use flow-through ponds for rearing; the flow-through ponds use cement ponds, with a single pond area of 30-90 sq m, a pond depth of 60-80 cm, and a water depth of 50-60 cm. The pond width is 1.2-2.5 m. The bottom slope is 2:1000 to 5:1000. The water flow rate of the flow-through pond is 100-300 L/min, maintaining a water depth of 50-60 cm. Adjust the stocking density according to the growth size of the Hucho taimen. For fingerlings of 5 g, the stocking density is generally 1,000 individuals/sq m; for fingerlings of 10 g, the stocking density is generally 800 individuals/sq m; for fingerlings of 20 g, the stocking density is generally 600 individuals/sq m; for fingerlings of 30 g, the stocking density is generally 500 individuals/sq m.
4. Adult fish farming
(1) Flow-through pond farming: Use cement ponds. The cement pond is rectangular, with an area of 200 sq m, a pond depth of 100 cm, and a water depth of 80 cm. The pond width is 6.67 m, the pond length is 30 m, and the pond bottom slope ratio is 12:1000. The ponds are arranged in parallel. Choose groundwater with a relatively low water temperature as the water source. The suitable growth water temperature for the Hucho taimen is 13-20°C, the optimal growth water temperature is 13-16°C, and the maximum water temperature must not exceed 20°C. The pond water exchange rate should be above 2 times/hour, and the flow velocity should be maintained at 0.02-0.16 m/s. The dissolved oxygen in the water should be above 6 mg/L, and ammonia nitrogen should be controlled below 0.0075 mg/L. For fingerlings of 20-50 g, the stocking density is generally 150-300 individuals/sq m; for fingerlings of 100 g, the stocking density is generally 150 individuals/sq m; for fingerlings of 150 g, the stocking density is generally 100 individuals/sq m; for fingerlings of 200 g, the stocking density is generally 75 individuals/sq m; for fingerlings of 300 g, the stocking density is generally 50 individuals/sq m.
(2) Lake enhancement: It is advisable to choose waters in lakes with dense aquatic plants (coverage preferably reaching above 90%), clear and transparent water, no pollution, a maximum summer water temperature not exceeding 20°C, dissolved oxygen in the water not lower than 5 mg/L, and a total suspended solids content in the water not higher than 15 mg/L for release and enhancement. The waters should also have abundant benthic animals, aquatic insects, small fish and shrimp, and other food organisms. Both juvenile and 1-year-old Hucho taimen fingerlings can be stocked. The suitable juvenile size is 3-5 cm. The suitable stocking density is 10-30 individuals/mu. The suitable size for 1-year-old fingerlings is about 25 g, and the suitable stocking density is 5-10 individuals/mu. The Hucho taimen has the habit of migrating to the depths of large rivers to overwinter in late autumn and early winter, and harvesting is generally carried out from late September to early October; otherwise, the Hucho taimen will dive into the depths of the lake to prepare for overwintering and will be very difficult to catch.