How to carry out fry and fingerling rearing in mandarin fish aquaculture

Over the past ten years, mandarin fish fry rearing techniques have been continuously improved and enhanced, and the rearing methods have also become diverse, from the earliest pond rearing to factory-based fry rearing under artificially controlled conditions. Among them, the rearing methods currently considered relatively ideal include: hatching circular channel (tank) rearing, cage rearing, small cement tank rearing and small earthen pond rearing, etc. In production, two or more of these forms are often combined. The specific methods often vary from place to place.

1. Hatching circular channel (tank) rearing The circular channel is a special water body; it simulates natural ecological conditions and keeps the fish eggs continuously rolling. Directly using the circular channel to rear fry provides the living environment required by mandarin fish fry, and more importantly, when the mandarin fish fry begin to feed, it allows feeding of suitable-sized bait fish——other live fry that have not long hatched, which not only satisfies the nutrition needed for the growth and development of mandarin fish fry, but also helps maintain fresh water quality. During the rearing of mandarin fish fry, attention should be paid to the shortcoming that the circular channel is not easy to drain, so as to prevent the accumulation of silt and humus in the circular channel. After 5-7 days of rearing, a sunny day should be chosen and the fry should be transferred to another circular channel at around 10 a.m. Mandarin fish fry are greedy feeders, so it is best to stop feeding bait fish 12 hours before transferring, to ensure that they have empty stomachs during transfer and reduce losses.

2. Cage rearing Cages are an ideal place for rearing mandarin fish fry. They can ensure sufficient and easily obtained bait, and also allow relatively fresh water to be continuously exchanged. The shortcoming is that bait fish that have just hatched cannot be fed, the cages need to be washed frequently, the cages need to be replaced regularly, and fry management is rather cumbersome and relatively difficult to operate. Cages generally adopt a three-stage rearing method: Stage I cages are open-top cages sewn from 40-28 mesh/3 cm polyethylene netting, 4-6 m long, 1 m wide and 1 m deep; Stage II cages are open-top cages sewn from warp-knitted polyethylene netting with a mesh size of 0.3 cm, 2 m long, 1 m wide and 1 m deep; Stage III cages are open-top cages sewn from warp-knitted polyethylene netting with a mesh size of 0.5 cm, 2 m long, 1 m wide and 1 m deep. The supporting area ratio of Stage I, II and III cages is 1:10:20.

3. Cement tank rearing Cement tanks are generally 4 m×6 m×0.8 m, and may also be slightly larger or smaller. However, the bottom must have a certain slope, and a fry collection pond should be set at the bottom drainage point, with water inlet and drainage devices. The drainage device is composed of a rubber hose, a filter screen and supporting iron wire; the rubber hose opening is fixed at the center of the iron wire frame, and no matter how it is placed, it is required not to drain the pond water completely, so as to maintain a certain water level. The drainage flow rate is controlled by the number of drainage pipes and the height of the water outlet.

4. Small earthen pond rearing When mandarin fish grow to about 3.0 cm, they can be put into small ponds for rearing, with a stocking rate of about 150,000 fry/hectare. Bait fish must be cultivated in the pond in advance. Generally, bait fish fry are stocked 10-15 days before the mandarin fish fingerlings are stocked, at a stocking rate of 15-22.5 million fry/hectare. A small amount of fresh water should be added regularly every day to guard against deterioration of water quality.