Detailed Explanation of the Technical Regulations for Grouper Breeding and Seedling Rearing

Water for seedling rearing: use directly after sand filtration

Main facilities:

(1) Water supply facilities include 1 sand-filtered water well, 1 set of submersible pumps, 1 sand filter tank, 1 reservoir tank and 1 set of inlet and outlet pipes;

(2) Aeration facilities include 1 set of blowers, 1 set of aeration pipes, aeration heads (2-4 per sq m); (3) 1 seedling rearing workshop containing ten seedling rearing tanks (specifications 2.5*4*1.2 cubic meters). Several temporary holding net cages (60*100 sq cm), 1 set of stainless steel sieving nets, 1 set of filter screens, and several fiberglass hatching barrels.

Fish eggs are self-supplied

Water quality standards: dissolved oxygen ≥5mg/L, pH 7.8-8.4, salinity 28‰≤S≤33‰, ammonia nitrogen ≤0.3mg/L, nitrite ≤0.01mg/L, water temperature 25℃≤T≤32℃

Breeding process

1 Treatment and hatching of fertilized eggs: use a 100-mesh silk screen to soak the fertilized eggs in disinfected seawater containing 20ppm povidone-iodine for filter-washing and disinfection for 2-3 minutes, then pour them into fiberglass hatching barrels at a density of 800,000-1,000,000 fertilized eggs per cubic meter of water for hatching (dim light, weak aeration), with the water temperature maintained at 29.5℃-30.5℃. After about 20 hours of hatching, the larvae can hatch out, and the larvae can also continue to be held temporarily in the hatching barrels. The hatching water is purified with 5-8ppm Huojunwang + 0.6ppm Dapaowang to maintain water quality. When the larvae begin to show feeding movements 40 hours after hatching, they must be fed immediately, using artificial compound feeds such as shrimp flakes and Bp filtered through a 250-mesh screen (acclimation and feeding induction). Two hours after feeding, transfer them with a silk-screen dip net to the seedling rearing tanks to continue cultivation, at a rearing density of 3000-5000 fish per sq m.

2 Treatment of water for seedling rearing: while hatching the fertilized eggs, fill the seedling rearing tanks with water to 0.8-1.0 m, then use 3-5ppm Huojunwang + 0.1-0.2ppm Yishengjian to activate and purify the water quality. After adding the larvae, drain and exchange 10-30 cm of water daily, and after each water exchange replenish 3-5ppm Huojunwang. Throughout the breeding process, appropriately siphon off sediment according to the cleanliness of the tank bottom to keep it clean, avoid water quality deterioration, and keep aeration in a boiling state at all times.

3 Feed types and feeding: the feeds used in the seedling rearing process include artificial compound feeds, rotifers, copepods, and brine shrimp nauplii and adults. From when the larvae begin to feed until they metamorphose into juveniles, feed artificial compound feed 3 times a day (at 5:30, 9:30 and 15:30), and the feed must be filtered through a silk screen before feeding; at 8 a.m. feed live food once (rotifers or copepods or brine shrimp nauplii), and the live food must be cleaned and disinfected before feeding. In addition, frequently check the amount of live food in the water, ensuring that the amount of live food in the water is greater than 1 per milliliter, to avoid self-cannibalism due to hunger. After the larvae metamorphose into juveniles, feed artificial compound pellet feed twice a day (at 8:00 and 14:00), and the pellet feed should be softened with lactic acid bacteria liquid to increase palatability and strengthen the physique, and feed brine shrimp adults or copepods once (at 5:30), which likewise must be cleaned and disinfected before feeding. 

4 Grading of juveniles: when it is estimated that more than 90% of the juveniles in the seedling rearing tank have [metamorphosed], immediately use stainless steel sieving nets to grade them, placing juveniles of the same size into the same temporary holding net cage, at a temporary holding density of 2500-3000 fish per cage, to avoid self-cannibalism due to uneven size; juveniles should generally be sieved and graded once every 2 days.

5 Removal from tank and counting of juveniles: juveniles can be removed from the tank once their body length reaches more than 3 cm. Generally a 300-milliliter plastic bowl is used for counting, usually with the standard of how many fish per bowl.

6 Disease prevention and control: (1) To prevent larvae from tangling together and dying due to poor vitality and juveniles from dying from cramping due to fright, generally use Gaowenc once a day during the seedling rearing period to improve the vitality and stress resistance of the fry. (2) To improve the metamorphosis survival rate of the larvae, use Su'an once a day during the metamorphosis period.