The Main Techniques of Producing Artificial Nursery for Portunus trituberculatus

Three-ported crabs are large-scale edible crabs, and their growth speed is fast. Artificial breeding can grow into commercial crabs in the year. It is an excellent breed of artificial breeding. However, the species of crabs currently used for aquaculture in our area are basically from natural sea areas. In order to improve the artificial breeding technology of the crab, and promote the development of the industrialization of swimming crab culture in our area, the author conducted a productive artificial nursery test of the crab from 1999 to 2000, and obtained a success and preliminary explored the practical method of raising seedlings in accordance with Zhoushan. The main points of the artificial breeding techniques of the crab are summarized below for reference.

I. Parent crab rearing

As an egg-bearing crab used for nursery purposes, it must have strong vigor, no trauma, good appendages, firm egg mass, clear edge of egg mass, and light yellow or brownish yellow eggs. It is not advisable to use pro-crab eggs that are mature or nearly mature so as not to abortion due to changes in the external environment during transportation or entering the room. The size of the pro-crabs is preferably 300 to 400 g/tail, and if the individuals are too large, it will cause the embryonic development to be out of synch, which will make it difficult to raise the seedlings.

1. Holding pool

The pro-crab holding pool is suitable for 20-80 m2 and the water level is 0.8-1 m. Before the pro-crabs enter the room, wash and disinfect the pool. The bottom of the pool is sanded with 10 to 15 centimeters, the sanded area accounts for about 60% of the pond area, and 40% of the gap is left near the drain outlet. It is used for feeding, draining water, removing residual baits, and then loading inflatable stones. The top and all sides are covered with black plastic film to protect the light.

2. Holding management

After the pro-crab is bathed in 30010?6 formalin for 20-30 minutes, it is put into the pro- crab pool. The depth of the pool water is 0.8-1 meter. The water temperature is natural water temperature, but it can also be warmed as needed, but it can be cultivated in crabs. During the period, the water temperature should not exceed 23°C. Daily water exchange rate 50% to 80%, pay attention to change the water temperature as much as possible does not exceed 0.5 °C, the proportion of difference does not exceed 0.001, the daily temperature change does not exceed 1 °C; during the holding period, 24 hours of uninterrupted air inflation, the amount of water for the surface was In the form of microwaves, EDTA in the water is maintained at 3 to 5 mg/l, norfloxacin 1 mg/l, furazolidone 2 mg/l, and formalin 2010-6 to inhibit the growth of bacteria and parasites; Shell fresh shellfish, such as dumplings, variegated rice dumplings, etc., with an amount of about 20% of the crab's body weight as a dumpling; daily suction to remove the residual bait and feces in the pool, when the pro-crab appendage offspring is found to increase It is very likely that the bottom sand becomes dark, and the pool must be poured in time to clean and disinfect the sand. At the same time, the pro-crab should be soaked and disinfected with potassium permanganate.

Second, larval rearing

1. Collection of larvae

The larvae were collected by the hanging cage method. After the matured broodstock eggs were bathed in 10 mg/L malachite green for 30 minutes, they were suspended in a nursery pond at a density of 1 per cage. The temperature difference between the temperature of the pro-pool and nursery pool should not exceed 0.5°C. Under the conditions of normal temperature cultivation, the density of larvae should be controlled within 50,000/m3, the density is too large, the cultivation is difficult, the final survival rate is low, and even the cultivation fails.

2. Cultivation of water temperature

In the case of temperature control, larvae are preferably grown at 22-26°C. The temperature of larval rearing in this experiment ranged from 22.5°C to 28°C and no harm was caused to the larvae. However, in the Z1 period, the water temperature below 23°C is good and should not be too high.

3. Inflate

The density of aerated stones in larval rearing should be controlled at 1/m2 or more. The amount of inflation Z1~Z2 is in the form of microwave, and Z3~Z4 is inflated and intensified until the large-eye larval stage and the juvenile crab period are boiled. It should be noted that when changing the water, the air volume should be adjusted in time with the change of the water level of the pool water. To prevent bursting the bottom membrane, causing a "pan bath."

4. Change the water

From the first day of Z1, adding water 20 centimeters a day, to the highest water level, the daily water change 20%, change the water during Z1, to grasp the temperature difference as far as possible not more than 0.5 °C; Z2 ~ Z4 on the 30% to 60%; Big eye larval stage and juvenile crab period based on water quality, daily water exchange rate of 80% to 150%. When the water change amount is increased to more than 60%, it is changed in three times a day, and the water change does not exceed 30% each time. Change the water after hanging the net and use the method of entering the side row to keep the water level stable.

5. Feeding

For bait raised by larvae, biological live baits such as monocytes and rotifers are preferred in the Z1 phase. When the biological live baits are insufficient or lacking, they can be replaced by a mixture of spirulina powder, BP, shrimp chips, yeast powder, and soymilk. The dosage is 4 to 6 mg/l; Z2 to Z4 to microcapsule feed (MED). The main dosage is 6-10 mg/L, and moderately hatched larvae are added. From the M phase, the adults of the larvae are mainly fed, and the dosage is 100% to 150% of estimated larvae weight. , and a small amount of feed MED bait. The feeding interval is 3 hours. This way of feeding can greatly reduce the amount of live insects and reduce production costs.

6. Pour pool

With the increase of feeding amount in larval rearing, more residual bait and feces may accumulate at the end of Z4 or M period, and the pool may be inverted depending on the sediment quality. The inverted pool can be carried out in the Z4 and M phases, but the larvae must be in the “experienced” time. If the larvae are young, they are most likely to withstand environmental mutations and die in large numbers. Inverted pools can use light-induced methods, that is, in the evening the larvae will be trapped in a corner with light, and then use buckets of water to dip into the pool with fresh water, and the remaining small amount of larvae will be collected by a drainage cage.

7. Hanging net

When the Z4 larvae are all metamorphosed into large ocular larvae and the color turns black, they can be slung. Hanging net density is determined by the density of larvae in the pool, which is generally 0.5 m 2 per cubic body of water. It is better to use a white "mesh net" as the mesh. After lifting the net, care should be taken in the management not to expose the net to the surface of the water, so as to prevent the larvae from dying.

8. Disease prevention and treatment

(1) Countermeasures for backstab breaking. In the case of portuny crabs, Z1 larvae often suffer from backstab breaks, that is, the newly generated Z1 larvae are all normal in vigor and form. However, from the afternoon of the second day, the larvae begin to show the backspin fracture and continue to fester until the backstab Only the roots remained, and the larvae could not be transformed into Z2. The reason for backstab breaking is still unknown. This experiment has found out that as long as drugs (such as norfloxacin, SMZ+TMP, etc.) are used to inhibit backstabbing, most of the larvae can still normalize to Z2. The effect of drug inhibition is preferably lower than 23°C, and the effect of excessive water temperature is extremely poor.

(2) Prevention and control measures of polydipsia and piperculosis. For the prevention of these two parasites, the nursery water is treated with a disinfectant containing more than 3 mg/l of available chlorine for more than 2 hours, and then neutralized with an appropriate amount of sodium thiosulfate to confirm that there is no residual chlorine; use it for pro-crab use 10 mg/L malachite green bath; P. elegans were washed with 2% bleach before hatching, and then incubated with 30010-6 formalin for 5 to 10 minutes after hatching. To avoid or reduce pathogens into the nursery pool. For onset larvae, 0.1-0.2 mg/L malachite green or 5010-6 formalin can be used for 24 hours and then a large amount of water is changed for treatment. However, both malachite green and formalin have strong side effects on larvae and should be avoided if possible.

(3) Vibrio disease control measures. The abdomen and backstab of larvae suffering from vibriosis showed diffuse redness and gradually expanded to the whole body. The vigor of the larvae was poor, and the phototaxis was weakened. Anorexia caused a large number of deaths during the metamorphosis. Vibriosis can occur at every stage of larval development. In addition to the same preventive measures as parasites, the disease is usually treated with alternating doses of 1 to 2 mg/L of norfloxacin, SMZ+TMP, and Razor Hydration.

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