Detailed Explanation of Key Points of Raceway (Flowing Water) Farming Techniques for Rainbow Trout

The rainbow trout is named for the brownish-red longitudinal stripe along the lateral line of its adult body, resembling a rainbow. Rainbow trout has advantages such as delicious flesh, rich nutrition, few bones and much meat, high edible value, rapid growth, and simple and easy artificial breeding. It has now become one of the four major freshwater aquaculture species with high yield and excellent quality promoted worldwide by the Food and Agriculture Organization of the United Nations, and is listed as a high-grade fish. Rainbow trout live in water temperatures of 2°C to 25°C, with the optimum water temperature being 12°C to 20°C. They have wide adaptability, and can be farmed both in ponds and stocked in reservoirs, lakes, and rivers. Especially when raised in flowing water, they can grow all year round with very high yields. Large-scale farming practice has shown that the general yield per mu is 30,000 kg to 35,000 kg of marketable fish, with the highest reaching over 50,000 kg. Therefore, the prospects for raceway farming of rainbow trout are attractive.

I. Construction and Layout of Fish Ponds

A well-equipped farm should, according to the different growth stages of rainbow trout, have fry ponds, fingerling ponds, yearling ponds, marketable fish ponds, broodstock ponds, and reserve broodstock ponds, with their areas accounting for 0.5%, 1.0%, 12.5%, 80%, 3.0%, and 3.0% of the total area respectively. Where conditions permit, a small number of quarantine ponds should also be set up for isolating and quarantining diseased fish. Fry ponds, fingerling ponds, and yearling ponds are best built with stone masonry or concrete structures, while marketable fish ponds and broodstock ponds can be either earthen or stone masonry or concrete structures. Regardless of the structure of the fish pond, the determination of its shape must take into account smooth water flow, easy waste discharge, full utilization of land, and reduction of construction costs. The layout of various fish ponds is as follows: fry ponds, fingerling ponds, and yearling ponds are placed in front, while marketable fish and broodstock ponds are behind. Quarantine ponds must use water separately, and the discharged water cannot be reused. According to the terrain, each row of fish ponds must have a certain drop to facilitate natural water flow.

Each fish pond must have an inlet, an outlet, and a waste discharge outlet. The size of the inlet and outlet should be determined according to the water flow rate, flow velocity, pond size, pond shape, water inlet method, and required number of water exchanges. If using straight-flow inlet and outlet, the openings should be somewhat wider to facilitate oxygenation; if using spray or sprinkle methods for water inlet, the size of the openings should be designed according to the required flow rate, water pressure, and flow velocity requirements. Fish screens must be installed at both the inlet and outlet to prevent fish from escaping. The fish screens must be tight, and the spacing should be determined according to the size of the fish.

II. Feeding and Management

The entire feeding process of rainbow trout, starting from hatching out of the egg membrane, can be divided into several stages: the fry stage (from hatching to two months after first feeding), the fingerling stage (from two months to 6 months after first feeding), the yearling stage (from 9 months after first feeding to the end of the year), and the marketable fish stage (from January of the second year to sale).

Within 20 days after hatching, the fry rely on the nutrients in their yolk sac to maintain growth and development, and 10,000 to 50,000 fish can be stocked per square meter. At 20 days after hatching, feeding begins. Initially, cooked egg yolk can be mixed into a slurry and dripped into the fish pond. One month after first feeding, 500 to 1,000 fish can be stocked per square meter. Cooked egg yolk can be squeezed through gauze so that the yolk drips into the water in fine particles, and afterward the egg white can also be used together. Animal liver and fresh small trash fish can also be ground into a paste and dripped onto the water surface for feeding. Feed 6 to 8 times per day. The daily feeding amount can account for 12% of the fish body weight.

Two months after first feeding, the fry have reached about 1 gram in body weight and have entered the fingerling stage. 200 to 500 fish can be stocked per square meter. At this time, pellet feed can be used entirely. However, the animal-based components in the feed must be maintained above 80%. The daily feeding amount can account for about 9% of the fish body weight, with 4 feedings per day. Half a year after first feeding, until the end of the year, is the yearling stage, and 50 to 200 fish can be stocked per square meter. Marketable-fish feed can be used, with the feeding amount accounting for about 5% of the fish body weight and 3 to 4 feedings per day.

During the marketable fish stage, 15 to 50 fish can be stocked per square meter, with a water depth of 1 m to 2 m. Animal-based feed accounts for 30% to 40% of the feed, and plant-based feed accounts for 60% to 70%. The pellet size should be suitable for mouth size, generally 4 mm to 8 mm in diameter, fed twice a day, with the feeding amount being 2% to 3% of the total fish weight. To achieve high yields of marketable fish, in terms of management, the first priority is to maintain sufficient water volume and install aeration equipment; once oxygen deficiency occurs, it must be replenished immediately. Second, marketable fish that have reached the edible standard must be frequently caught and sold in a timely manner, and individuals showing obvious differences should be selected and placed in separate ponds for rearing.