At 4 to 7 days of age, the survival rate during this period is very low. It has been recorded that at 7d of hatching, the survival rate of grouper fry is <10%, and even total loss is common.

The main reasons include poor egg quality, congenital deformities, and inability to open their mouths to feed. In addition to the above reasons, the lack of essential bio-physiological active substances in the bait makes it difficult for the young fish to complete the transition from endogenous to exogenous nutrition, which is an important reason for the poor survival rate of the young fish. Therefore, various measures should be taken in the nursery:

Cultivate and maintain sufficient amount of rotifers, algae and other biological baits in the water.

When individual fry are found to have opened their mouths, they should be fed spirulina powder of 0.5 grams per cubic meter (filtered through a 250-mesh sieve) or appropriate amount of pond water should be pumped into the hatchery box, so as to let the fry that have opened their mouths first to feed in time and to let the others get used to the taste of foraging.

Feeding of palatable, adequate amount of bait with the opening, such as spirulina powder and shrimp pieces of 200 to 300 grams / mu - m + 1 mu / bottle of King of big bubbles + multi-dimensional 200 grams / mu + bivalent yeast 200 grams / mu + the right amount of water mixed with soaking for 2 to 3 hours after sprinkling, 2 times / day, feeding for 3 days; the first day to use the first day of the 250 purpose of the sieve silk screen filtered feeding, the second two days after the second day of the 200-mesh filtered silk screen filtered feeding; the purpose is to entice the strengthening of the feeding of the fish, and to let the other fish to adapt to the taste of foraging. The purpose of feeding is to induce food to strengthen the nutrition of the water body and enhance the appetite of the young fish.

After hatching for about 12 to 15 days, it is in the later stage of the young, when the fish have grown long dorsal and ventral spines, the internal organs are further developed, and the external morphology has also changed greatly.

This stage of the baby fish has the habit of clustering, if the fry's vitality is not good, then the fry's "wings" are easily entangled together, resulting in the phenomenon of dead fish; in addition, overly dense is also prone to cause the local sub-deficiency of oxygen, resulting in the poor vitality of the fry.

The following measures have obvious benefits: no lights are turned on in the nursery pond at night to keep the water quality fresh and prevent the moss from growing due to sticky fertilizer sinking to the bottom, and timely removal of filamentous algae from the bottom and sides of the pond to reduce the deaths of the fry entangled with the moss. At this stage, it is best to use every two days, high stability C + speed an (1 + 1 with 1.5) mu to increase the oxygen to sticky, enhance the physical quality of the fish fry to improve the vitality of the fish fry, to reduce the suboxicity caused by poisoning of the fish fry vitality is not good.

After 16 to 25 days after hatching, there are many reasons why the fish fry are easy to die during the period of withdrawal of fins:

First of all, the water body is malignant, and the content of ammonia and nitrogen and organic matter in the water is too high, therefore, it should be appropriate to use water toxins to clean the water and sprinkle the water in 2 mu/package to detoxify the water.

The second is due to the growth and development of the fry caused by the size of the fry, coupled with the grouper fry have self-mutilation habits, this stage of the grouper fry have appeared to attack and kill each other, the grouper fry eating each other is quite serious.

Often can be observed: the individual size of the same fish, a larger fry swallowed another smaller fry half, the larger fry was stuck, the smaller fry was bitten to death, the size of the two fish died together; there are also bitten fish to stay at the edge of the pool, often chased; a small number of ingesting the same kind of individual growth accelerated, and later more prone to mutilation of the same kind of people. The self-mutilation habit has a great impact on the survival rate of nursery. Feeding halibut larvae at the most serious stage of grouper feeding on each other can reduce the phenomenon of feeding on each other. Because this stage is mainly feeding copepods, and the size of copepods is no longer very suitable for the caliber of large fry, and need to find some big food. After feeding halibut larvae, the fish can ingest palatable bait at any time, and predation will be reduced accordingly. When the fish grow to 5cm, the phenomenon of mutual predation will be reduced naturally.