Spotted grouper breeding techniques are more difficult, the main reasons are: (1) small larvae out of the film, a total length of about 1.6mm, activity is weak; (2) feeding live bait, bait cultivating many links, difficult to control , Oftentimes, the supply of bait is not timely; (3) The scope of adaptation to environmental conditions is narrow and man-made control is difficult. For these reasons, the nursery effect is unstable. The author started preparations in August 1998 and conducted research in aspects such as food preparation, environmental condition control, and management measures in October and December 1998, January and December 1999 and January and April 2000, respectively. 58 batches of spot grouper artificial breeding trials were conducted successively, and the test results are reported below.
1 Seedling pool and water treatment indoor cement pool, rectangular, area 10m2 (4m2.5m), pool depth 1m. Easy to enter and drain, control temperature and adjust light. 12 gas stones are inflated per pool. Water for nursery needs to be clean and sand-filtered before use.
2 Seedling environmental conditions
2.1 Water temperature The appropriate water temperature for larvae is 24-29°C. The larvae below the water temperature of 22°C cannot open the food. The survival rate of larvae at 22-24°C is very low, and the larvae activity at 30-3l°C is not normal. The juvenile period has a slightly wider temperature range.
2.2 The amount of dissolved oxygen generally requires that the amount of dissolved oxygen in the nursery pool be kept above 4mg/L.
2.3 Ammonia nitrogen in the nursery, the ammonia nitrogen content is a water quality indicator that needs special attention, the general requirement does not exceed 0.7mg/L. In the nursery test, the authors found that larvae with 1-2cm ammonia nitrogen content of 1.2-1.5mg/L had abnormal activity. These fish could not sink, but only moved on the water surface. Its activities are characterized by: the body sideways on the surface of the water, or the head lifted, the body and the surface of the water is about 45 °C rapid movement in the water, or the longitudinal axis of the body is about 45 °C fast travel, etc., a few hours later Found dead fish at the bottom of the pool. After a large number of water changes, the ammonia nitrogen content dropped below 0.3 mg/L to be alleviated.
2.4 The light test found that the suitable light intensity range of the nursery pond water surface was 5000-15,000 lx, and the optimum range was 6000-8000 lx. When the illumination is lower than 5000 lx, the larvae develop slowly, and it is difficult to open the food; the light is too strong and the algae in the nursery pond grow extremely fast, which is unfavorable to the growth of the fry, especially in the week after the opening of the larvae. death. 2.5 The hatching rate of spawning grouper with salinity and hatching water with a salinity of 30-33 is higher, and the hatching rate is decreased with the decrease of salinity. The salinity of water in the early stage of nursery is the same as that of the hatching water, and the salinity can be gradually reduced in the later period of nursery.
3 seedlings
3.1 Preparation before laying seedlings
3.1.1 Nursery pond disinfection Usually, the bottom of the pond and the wall of the pond are brushed, and the bleaching powder is sterilized. Rinse 3-4 times until no chlorine is detected with sodium thiosulfate.
3.1.2 Adjust lighting requirements Illumination hours above 11h, noon maximum water intensity 6000 ~ 8000lx. In general, the light intensity of the nursery season is higher than this value, and shading nets can be placed above the nursery pond to adjust the light intensity.
3.1.3 In the initial stage of raising water in nursery, the water depth is 40cm. Inoculate some unicellular algae and establish a stable ecosystem as soon as possible in the nursery pool to ensure that the water quality does not change too quickly. It can also be used as a bait for rotifers. Usually, fresh water is injected one day before the seedlings are sown, and 40-60L of concentrated chlorella liquid, 2.5-5L of liquid gold algae, and 15 ml of concentrated marine yeast are added per cubic meter of water.
3.2 Putting the seedlings with the grouper The fertilized eggs are incubated for about 20 hours under suitable conditions of water temperature and salinity. The newly hatched larvae can enter the nursery pond on the same day. The seedling density was 30000 to 50 000 tails/m3. Pay attention to the appropriate water temperature and salinity when releasing the seedlings. The water temperature difference between the incubating water (or inside the packaging bag) and the nursery pond should not exceed 1°C, and the salinity difference should not exceed 3‰. Put the fry slowly into the pool. The fry who had just been in the pool gathered in the corner of the pool and there were many layers above.
4 Feed and Feeding Methods Before growing seedlings, prepare various kinds of bait and change different types of bait according to different developmental stages. Replacing bait should pay attention to: (1) Each time the bait is changed, there must be a 2–3d transition time so that most fish can adapt well to new bait; (2) Replacing bait should be timely, too late to affect the growth of fish, too early Since most individuals cannot eat, they are not only wasteful, but also cause uneven growth. Individuals who can ingest larger foods grow particularly fast.
4.1 Open-baited spot fish with grouper larvae are usually fed on the 3rd to 4th day of the membrane, with the water temperature 24~26°C opening on the 4th day and the 26th–28°C on the 3rd day. The larvae have two distinct characteristics when they ingest food: (1) the eye's melanin pigment and abdominal melanin pigment have been observed with the naked eye; (2) the larvae are placed in a glass and can be seen to strongly impact the wall with a snout or The bottom of the cup. Once the larvae are found to have food ingestion, they should be fed in a timely manner to ensure that the larvae receive adequate nutrition. After feeding larvae, they feed the shellfish larvae in the first 3 days, and they can also directly feed mature eggs of certain animals, such as eggs, oyster eggs, and sea urchin eggs. Feed 4 times a day, each time a cubic gram of egg shellfish (or sea urchin eggs) is fed in a cubic meter of nursery water. Sprinkle the whole pool evenly and put a small amount of rotifers on the second day of larval opening.
4.2 On the 4th day of the rotifer feed, shellfish larvae (or shellfish, sea urchin eggs) were stopped feeding, rotifers were mainly fed, and copepods were no nauplii. Due to the low content of unsaturated fatty acids in rotifers, they can not meet the nutritional needs of larvae. The rotifer enhancer was used for intensive cultivation before rotifers were fed. During this period, the rotifer density of the nursery water body was maintained at 10,000 to 20,000 per liter. Feeding rotifers takes about 10 days.
4.3 Copepods When fish fry begin to grow with dorsal and ventral spines (approximately 14 days of age), their activities are enhanced, and they can be fed with copepods, keeping the density of copepods in nursery pools between 1000 and 2000. /L. It takes a long time for the grouper to use copepods as the main food. There are more than 20d (about the entire juvenile stage). At this stage, if the supply of copepods is in short supply, part of Artemia nauplii can be supplemented, and if necessary, some shrimp nauplii can be supplemented. At this point, it is easy to visually observe the fish's feeding conditions and whether it is satiety, and the actual operation can be based on whether the fish is full to increase or decrease the amount of feed fed.
4.4 Feeding of Chironomidae or frozen Artemia spotted grouper to a full length of about 2.5cm enters the juvenile stage. Frozen Artemia can be fed. Since frozen Artemia is a dead bait, feeding must be done a few times. Usually 3-4 times a day. Begin training for several days, and mix some live copepods with frozen Artemia and feed them slowly at poolside or poolside. Trained fish can gradually grab food in groups. The frozen Artemia was used as bait until it was 4 to 5cm in length.
If there are conditions, the chironomid larvae can be fed earlier in this phase. In the same way, the chironomid larvae are fed together with the copepods. The amount of the chironomid larvae is easily grasped, and it is advisable to feed it once for 2 to 3 hours and 2 times per day. Wait until the fish grows to about 3.5cm and then feed frozen Artemia. The use of Chironomid larvae for the transition has obvious advantages: (1) Individuals of chironomid larvae are larger than copepods and smaller than frozen Artemia, which is more suitable for fish at this stage; (2) Self-mutilation of small fish-eating small fish is reduced.
4.5 Shrimp or minced fish The grouper is 4-5 cm long and can start feeding shrimp or minced fish. 2 times a day, when the fry do not concentrate feeding, stop feeding.
5 Water Quality Management
5.1 When the larvae go out of the pool in the lower larvae of the film, the water depth is about 40cm, and there is no need to add water or change water before feeding larvae.
5.2 feeding shellfish eggs as long as the amount of shell eggs properly controlled, add water 2-5cm (water depth) every day, generally do not need to change the water, rely on the balance of algae and the appropriate water to maintain water quality and stability.
5.3 Feeding live bait After feeding the shellfish eggs, feed rotifers. During the day, pay attention to adjusting the density of rotifers, supplement them in time, ensure feeding of larvae, and add algae according to the water color in the evening. If properly controlled, only add water for a week without changing the water. When there are many bubbles on the surface of the water, there are many organic particles in the water, or when the ammonia nitrogen reaches 0.5mg/L, the amount of added water must be increased. If the nursery pond is close to the highest water level, it is necessary to start changing the water. Each change of water 1/4 to 1/3, generally first drainage, suction bottom, after adding water. Ensure that the water is fresh and maintain a depth of 90-95cm. After adding water, add algae solution to make the hue of the water a little stronger, which will help inhibit the growth of filamentous algae at the bottom of the pool. The latter can wrap fry and cause harm.
5.4 Feeding Frozen Artemia and Shrimp Once the start of the feeding of dead bait, the residual bait can easily contaminate the water quality. In addition, the food intake of the fish increases and the water quality is variable. At this stage, the water depth is generally kept between 45 and 55cm. The bottom is sucked and the water is changed once a day. It is not necessary to insert the monocytic algae. When the water temperature is high, change the water twice a day.
6 Intake and drainage, suction, transfer to the pool, seed collection operation and the breeding density at each stage
6.1 Intake, Drainage, Sewage Removal, Transferring to the Pool, and Collecting the Seedlings The operation method in the process of raising the seedlings with grouper is basically the same as that of seawater fish breeding, but there are several points to note:
6.1.1 Water injection During the feeding of shellfish larvae, the filter bag can be used to connect the water inlet. The bottom of the bag is immersed under the water surface of the nursery pond and slowly add water. After emergence of dorsal spine and abdominal spine, add a layer of screen mesh above 120 mesh to the outside of the filter bag when water is added, so as to prevent the long spiny thorns on the bag from being thrown out of the bag.
6.1.2 Drained fry before 3cm, according to its size, with the corresponding specifications of the sieve mesh made of water jacket, siphon drainage. When the total length reaches 4 - 5cm, the plastic basket can be directly placed on the drainage hole of the bottom of the pool for drainage.
6.1.3 Sewage suction, clean the bottom of the seedlings during the incubation period to keep the nursery clean and often suck the dirt, the fish full length 4cm before the siphon can be used to suck the bottom of the dirt, the fish full-length above 4cm can directly filter basket Cover the drain outlet and use a soft broom to gently sweep the dirt toward the drain while draining.
6.1.4 Before pulling the net and catching fry, the back spines and abdominal spines of the fry are not constricted. Generally, it is not appropriate to pull the net to catch the seedlings; Pull the bottom of the pool clean before pulling the net, and carefully catch the fish with a dense net. 6.2 Fish sieving specifications can only be used when the grouper's density at each stage reaches 3.5 to 4 cm. When the sifter is used, the sieve is suspended in water to allow the fish to escape freely. It is easier to operate after the fish grow up.
6.2.1 The seedling density of larvae is generally/m3.
6.2.2 The total length of less than 2cm of fish dorsal spine and abdomen spine at the end of the contraction, generally should not be moved. If the survival rate of the opening is high, the density of fry within the pool needs to be divided into pools. The maximum density is generally not more than 5000 tails/m3 (water depth is about 80cm).
6.2.3 For a total length of 4 to 6 cm, the cultivation density should be 400 "600/m2.
7 Discussion on several issues in nursery
7.1 With regard to the larvae's open-feed larvae, the larvae have small mouth cracks and can't eat rotifers. The current practice is to use yak collared fertilized eggs and larvae as open bait. However, there is not much time for oyster larvae in Hainan. The authors have tried oyster eggs, sea urchin eggs, and estuary eggs, and think that as long as the size is right, eggs that have undergone a large growth period can be used as larval opening baits. Unfertilized germ cells have the disadvantage of easily contaminating water quality, but they are more convenient to use, easy to obtain, and rich in nutrients. As long as they are well-controlled, they can successfully pass through the opening period and enter the stage of feeding rotifers. The specific method is: the first 3d of the opening is fed with shellfish eggs (or sea urchin eggs), 4 times a day, every time, 10g of water per cubic meter of nursery water, evenly sprinkling the whole pool, and feeding a small amount on the second day of larval opening Rotifers make a gradual transition to feeding rotifers.
7.2 About the danger period in the nursery process In 1993, Bozhili pointed out that in the breeding process of grouper, there are several stages of high mortality rate, which is called the dangerous period. Reducing the death of dangerous period is to improve the survival rate of nursery. The essential. There are also 3 danger periods in the spotted grouper nursery:
The first danger period is from 4 days to 10 days, and the survival rate during this period is very low. It is reported that the survival rate of grouper larvae was <10% after hatching for 7 days. According to reports, the annihilation of the entire army is also a common occurrence. It is generally believed that possible causes include poor oogenesis, congenital malformations, and inability to open food intake. The authors carried out trials on seedlings with grouper, and the results were also very unstable. The survival rate in the opening period was up to 70% and the lowest was 0. From the analysis of various situations, it is believed that except for the above reasons, there is a lack of essential bio-active substances in the diet, and it is difficult for larvae to complete the transition from endogenous nutrition to exogenous nutrition as an important reason for the low survival rate of larvae. Therefore, a variety of measures should be taken in raising seedlings: Feeding open baits that are suitable for palatability and nutrition to meet the needs; Feeding open baits in time, and larvae that do not feed in time due to lack of yolk sac are not dead at the time. Due to lack of nutrition, the vitality gradually weakens, and the survival rate is very low. When controlling the incubation water temperature and the temperature of the early nursery, when the water temperature is high, the metabolic consumption of larvae is too fast and exogenous nutrition can not keep up; the water quality is better, except for some chemical factors. In addition to the growth and development of Aberdeen, the particulate matter in the water adheres to the larvae, making it less viable.
The second danger period is at the late larval stage. At this time, the fish have already developed long dorsal spines and abdominal spines. The internal organs are further developed and the external morphology is also greatly changed. Observed at this stage of the larval system to produce fluid, because the phototaxis is clustered with each other, excessive concentration, suffocation and death; sometimes observed in fish suddenly died after the water surface rotation, the reasons for further study. The authors found that there are obvious advantages to taking the following measures: At night, the nursery pool does not turn on the lights, keeps the water clean, removes the filamentous algae at the bottom of the pool, and pays attention to the nutrition of the bait to prevent the fish from being too dense.
The third danger period is when the body begins to appear after entering the juvenile period. During this period, it was quite serious to spot some groupers and they could often be observed: fish of similar size, one head biting the other, both fish died together; bitten fish stayed in the pool At the same time, he is often chased; a small number of individuals who feed on the same species grow faster, and later become more likely to eat the same type of food. Mutual food has a great influence on the survival rate of seedlings. This is the habit of grouper and it is difficult to change. However, the authors found that the feeding of chironomid larvae at the most severe stage of spotted grouper feeding on each other can make each other disabled. Food is reduced. Since this stage is mainly fed with copepods or frozen Artemia, the size of copepods is not suitable for the caliber of fish, and it is necessary to find some large foods; Frozen Artemia is a dead bait and cannot be fed all day long. After feeding the chironomid larvae, the fish can eat palatable feed at any time, and the amount of residual food is reduced accordingly. When the fish grows up to 5cm, the phenomenon of mutual gluttony naturally decreases.
7.3 With regard to the salinity test of nursery water, the spotted grouper developed to late larvae, and the salinity of nursery water can be gradually reduced to about 25, without adverse effects on the fish. On the other hand, nursery requires larger amounts of rotifers, copepods, and sometimes rotifers, copepods reproduce better under lower salinity conditions, or they are derived from lower salinity water bodies. If the biological feed derived from the lower salinity water body is fed to a nursery pond with a salinity of 30-33 ,, the bait creature sinks quickly and eventually dies. In this case, the salinity of the nursery water is gradually reduced, so that it can be adapted to the growth environment of the bio-feed and can achieve a better nursery effect.
1 Seedling pool and water treatment indoor cement pool, rectangular, area 10m2 (4m2.5m), pool depth 1m. Easy to enter and drain, control temperature and adjust light. 12 gas stones are inflated per pool. Water for nursery needs to be clean and sand-filtered before use.
2 Seedling environmental conditions
2.1 Water temperature The appropriate water temperature for larvae is 24-29°C. The larvae below the water temperature of 22°C cannot open the food. The survival rate of larvae at 22-24°C is very low, and the larvae activity at 30-3l°C is not normal. The juvenile period has a slightly wider temperature range.
2.2 The amount of dissolved oxygen generally requires that the amount of dissolved oxygen in the nursery pool be kept above 4mg/L.
2.3 Ammonia nitrogen in the nursery, the ammonia nitrogen content is a water quality indicator that needs special attention, the general requirement does not exceed 0.7mg/L. In the nursery test, the authors found that larvae with 1-2cm ammonia nitrogen content of 1.2-1.5mg/L had abnormal activity. These fish could not sink, but only moved on the water surface. Its activities are characterized by: the body sideways on the surface of the water, or the head lifted, the body and the surface of the water is about 45 °C rapid movement in the water, or the longitudinal axis of the body is about 45 °C fast travel, etc., a few hours later Found dead fish at the bottom of the pool. After a large number of water changes, the ammonia nitrogen content dropped below 0.3 mg/L to be alleviated.
2.4 The light test found that the suitable light intensity range of the nursery pond water surface was 5000-15,000 lx, and the optimum range was 6000-8000 lx. When the illumination is lower than 5000 lx, the larvae develop slowly, and it is difficult to open the food; the light is too strong and the algae in the nursery pond grow extremely fast, which is unfavorable to the growth of the fry, especially in the week after the opening of the larvae. death. 2.5 The hatching rate of spawning grouper with salinity and hatching water with a salinity of 30-33 is higher, and the hatching rate is decreased with the decrease of salinity. The salinity of water in the early stage of nursery is the same as that of the hatching water, and the salinity can be gradually reduced in the later period of nursery.
3 seedlings
3.1 Preparation before laying seedlings
3.1.1 Nursery pond disinfection Usually, the bottom of the pond and the wall of the pond are brushed, and the bleaching powder is sterilized. Rinse 3-4 times until no chlorine is detected with sodium thiosulfate.
3.1.2 Adjust lighting requirements Illumination hours above 11h, noon maximum water intensity 6000 ~ 8000lx. In general, the light intensity of the nursery season is higher than this value, and shading nets can be placed above the nursery pond to adjust the light intensity.
3.1.3 In the initial stage of raising water in nursery, the water depth is 40cm. Inoculate some unicellular algae and establish a stable ecosystem as soon as possible in the nursery pool to ensure that the water quality does not change too quickly. It can also be used as a bait for rotifers. Usually, fresh water is injected one day before the seedlings are sown, and 40-60L of concentrated chlorella liquid, 2.5-5L of liquid gold algae, and 15 ml of concentrated marine yeast are added per cubic meter of water.
3.2 Putting the seedlings with the grouper The fertilized eggs are incubated for about 20 hours under suitable conditions of water temperature and salinity. The newly hatched larvae can enter the nursery pond on the same day. The seedling density was 30000 to 50 000 tails/m3. Pay attention to the appropriate water temperature and salinity when releasing the seedlings. The water temperature difference between the incubating water (or inside the packaging bag) and the nursery pond should not exceed 1°C, and the salinity difference should not exceed 3‰. Put the fry slowly into the pool. The fry who had just been in the pool gathered in the corner of the pool and there were many layers above.
4 Feed and Feeding Methods Before growing seedlings, prepare various kinds of bait and change different types of bait according to different developmental stages. Replacing bait should pay attention to: (1) Each time the bait is changed, there must be a 2–3d transition time so that most fish can adapt well to new bait; (2) Replacing bait should be timely, too late to affect the growth of fish, too early Since most individuals cannot eat, they are not only wasteful, but also cause uneven growth. Individuals who can ingest larger foods grow particularly fast.
4.1 Open-baited spot fish with grouper larvae are usually fed on the 3rd to 4th day of the membrane, with the water temperature 24~26°C opening on the 4th day and the 26th–28°C on the 3rd day. The larvae have two distinct characteristics when they ingest food: (1) the eye's melanin pigment and abdominal melanin pigment have been observed with the naked eye; (2) the larvae are placed in a glass and can be seen to strongly impact the wall with a snout or The bottom of the cup. Once the larvae are found to have food ingestion, they should be fed in a timely manner to ensure that the larvae receive adequate nutrition. After feeding larvae, they feed the shellfish larvae in the first 3 days, and they can also directly feed mature eggs of certain animals, such as eggs, oyster eggs, and sea urchin eggs. Feed 4 times a day, each time a cubic gram of egg shellfish (or sea urchin eggs) is fed in a cubic meter of nursery water. Sprinkle the whole pool evenly and put a small amount of rotifers on the second day of larval opening.
4.2 On the 4th day of the rotifer feed, shellfish larvae (or shellfish, sea urchin eggs) were stopped feeding, rotifers were mainly fed, and copepods were no nauplii. Due to the low content of unsaturated fatty acids in rotifers, they can not meet the nutritional needs of larvae. The rotifer enhancer was used for intensive cultivation before rotifers were fed. During this period, the rotifer density of the nursery water body was maintained at 10,000 to 20,000 per liter. Feeding rotifers takes about 10 days.
4.3 Copepods When fish fry begin to grow with dorsal and ventral spines (approximately 14 days of age), their activities are enhanced, and they can be fed with copepods, keeping the density of copepods in nursery pools between 1000 and 2000. /L. It takes a long time for the grouper to use copepods as the main food. There are more than 20d (about the entire juvenile stage). At this stage, if the supply of copepods is in short supply, part of Artemia nauplii can be supplemented, and if necessary, some shrimp nauplii can be supplemented. At this point, it is easy to visually observe the fish's feeding conditions and whether it is satiety, and the actual operation can be based on whether the fish is full to increase or decrease the amount of feed fed.
4.4 Feeding of Chironomidae or frozen Artemia spotted grouper to a full length of about 2.5cm enters the juvenile stage. Frozen Artemia can be fed. Since frozen Artemia is a dead bait, feeding must be done a few times. Usually 3-4 times a day. Begin training for several days, and mix some live copepods with frozen Artemia and feed them slowly at poolside or poolside. Trained fish can gradually grab food in groups. The frozen Artemia was used as bait until it was 4 to 5cm in length.
If there are conditions, the chironomid larvae can be fed earlier in this phase. In the same way, the chironomid larvae are fed together with the copepods. The amount of the chironomid larvae is easily grasped, and it is advisable to feed it once for 2 to 3 hours and 2 times per day. Wait until the fish grows to about 3.5cm and then feed frozen Artemia. The use of Chironomid larvae for the transition has obvious advantages: (1) Individuals of chironomid larvae are larger than copepods and smaller than frozen Artemia, which is more suitable for fish at this stage; (2) Self-mutilation of small fish-eating small fish is reduced.
4.5 Shrimp or minced fish The grouper is 4-5 cm long and can start feeding shrimp or minced fish. 2 times a day, when the fry do not concentrate feeding, stop feeding.
5 Water Quality Management
5.1 When the larvae go out of the pool in the lower larvae of the film, the water depth is about 40cm, and there is no need to add water or change water before feeding larvae.
5.2 feeding shellfish eggs as long as the amount of shell eggs properly controlled, add water 2-5cm (water depth) every day, generally do not need to change the water, rely on the balance of algae and the appropriate water to maintain water quality and stability.
5.3 Feeding live bait After feeding the shellfish eggs, feed rotifers. During the day, pay attention to adjusting the density of rotifers, supplement them in time, ensure feeding of larvae, and add algae according to the water color in the evening. If properly controlled, only add water for a week without changing the water. When there are many bubbles on the surface of the water, there are many organic particles in the water, or when the ammonia nitrogen reaches 0.5mg/L, the amount of added water must be increased. If the nursery pond is close to the highest water level, it is necessary to start changing the water. Each change of water 1/4 to 1/3, generally first drainage, suction bottom, after adding water. Ensure that the water is fresh and maintain a depth of 90-95cm. After adding water, add algae solution to make the hue of the water a little stronger, which will help inhibit the growth of filamentous algae at the bottom of the pool. The latter can wrap fry and cause harm.
5.4 Feeding Frozen Artemia and Shrimp Once the start of the feeding of dead bait, the residual bait can easily contaminate the water quality. In addition, the food intake of the fish increases and the water quality is variable. At this stage, the water depth is generally kept between 45 and 55cm. The bottom is sucked and the water is changed once a day. It is not necessary to insert the monocytic algae. When the water temperature is high, change the water twice a day.
6 Intake and drainage, suction, transfer to the pool, seed collection operation and the breeding density at each stage
6.1 Intake, Drainage, Sewage Removal, Transferring to the Pool, and Collecting the Seedlings The operation method in the process of raising the seedlings with grouper is basically the same as that of seawater fish breeding, but there are several points to note:
6.1.1 Water injection During the feeding of shellfish larvae, the filter bag can be used to connect the water inlet. The bottom of the bag is immersed under the water surface of the nursery pond and slowly add water. After emergence of dorsal spine and abdominal spine, add a layer of screen mesh above 120 mesh to the outside of the filter bag when water is added, so as to prevent the long spiny thorns on the bag from being thrown out of the bag.
6.1.2 Drained fry before 3cm, according to its size, with the corresponding specifications of the sieve mesh made of water jacket, siphon drainage. When the total length reaches 4 - 5cm, the plastic basket can be directly placed on the drainage hole of the bottom of the pool for drainage.
6.1.3 Sewage suction, clean the bottom of the seedlings during the incubation period to keep the nursery clean and often suck the dirt, the fish full length 4cm before the siphon can be used to suck the bottom of the dirt, the fish full-length above 4cm can directly filter basket Cover the drain outlet and use a soft broom to gently sweep the dirt toward the drain while draining.
6.1.4 Before pulling the net and catching fry, the back spines and abdominal spines of the fry are not constricted. Generally, it is not appropriate to pull the net to catch the seedlings; Pull the bottom of the pool clean before pulling the net, and carefully catch the fish with a dense net. 6.2 Fish sieving specifications can only be used when the grouper's density at each stage reaches 3.5 to 4 cm. When the sifter is used, the sieve is suspended in water to allow the fish to escape freely. It is easier to operate after the fish grow up.
6.2.1 The seedling density of larvae is generally/m3.
6.2.2 The total length of less than 2cm of fish dorsal spine and abdomen spine at the end of the contraction, generally should not be moved. If the survival rate of the opening is high, the density of fry within the pool needs to be divided into pools. The maximum density is generally not more than 5000 tails/m3 (water depth is about 80cm).
6.2.3 For a total length of 4 to 6 cm, the cultivation density should be 400 "600/m2.
7 Discussion on several issues in nursery
7.1 With regard to the larvae's open-feed larvae, the larvae have small mouth cracks and can't eat rotifers. The current practice is to use yak collared fertilized eggs and larvae as open bait. However, there is not much time for oyster larvae in Hainan. The authors have tried oyster eggs, sea urchin eggs, and estuary eggs, and think that as long as the size is right, eggs that have undergone a large growth period can be used as larval opening baits. Unfertilized germ cells have the disadvantage of easily contaminating water quality, but they are more convenient to use, easy to obtain, and rich in nutrients. As long as they are well-controlled, they can successfully pass through the opening period and enter the stage of feeding rotifers. The specific method is: the first 3d of the opening is fed with shellfish eggs (or sea urchin eggs), 4 times a day, every time, 10g of water per cubic meter of nursery water, evenly sprinkling the whole pool, and feeding a small amount on the second day of larval opening Rotifers make a gradual transition to feeding rotifers.
7.2 About the danger period in the nursery process In 1993, Bozhili pointed out that in the breeding process of grouper, there are several stages of high mortality rate, which is called the dangerous period. Reducing the death of dangerous period is to improve the survival rate of nursery. The essential. There are also 3 danger periods in the spotted grouper nursery:
The first danger period is from 4 days to 10 days, and the survival rate during this period is very low. It is reported that the survival rate of grouper larvae was <10% after hatching for 7 days. According to reports, the annihilation of the entire army is also a common occurrence. It is generally believed that possible causes include poor oogenesis, congenital malformations, and inability to open food intake. The authors carried out trials on seedlings with grouper, and the results were also very unstable. The survival rate in the opening period was up to 70% and the lowest was 0. From the analysis of various situations, it is believed that except for the above reasons, there is a lack of essential bio-active substances in the diet, and it is difficult for larvae to complete the transition from endogenous nutrition to exogenous nutrition as an important reason for the low survival rate of larvae. Therefore, a variety of measures should be taken in raising seedlings: Feeding open baits that are suitable for palatability and nutrition to meet the needs; Feeding open baits in time, and larvae that do not feed in time due to lack of yolk sac are not dead at the time. Due to lack of nutrition, the vitality gradually weakens, and the survival rate is very low. When controlling the incubation water temperature and the temperature of the early nursery, when the water temperature is high, the metabolic consumption of larvae is too fast and exogenous nutrition can not keep up; the water quality is better, except for some chemical factors. In addition to the growth and development of Aberdeen, the particulate matter in the water adheres to the larvae, making it less viable.
The second danger period is at the late larval stage. At this time, the fish have already developed long dorsal spines and abdominal spines. The internal organs are further developed and the external morphology is also greatly changed. Observed at this stage of the larval system to produce fluid, because the phototaxis is clustered with each other, excessive concentration, suffocation and death; sometimes observed in fish suddenly died after the water surface rotation, the reasons for further study. The authors found that there are obvious advantages to taking the following measures: At night, the nursery pool does not turn on the lights, keeps the water clean, removes the filamentous algae at the bottom of the pool, and pays attention to the nutrition of the bait to prevent the fish from being too dense.
The third danger period is when the body begins to appear after entering the juvenile period. During this period, it was quite serious to spot some groupers and they could often be observed: fish of similar size, one head biting the other, both fish died together; bitten fish stayed in the pool At the same time, he is often chased; a small number of individuals who feed on the same species grow faster, and later become more likely to eat the same type of food. Mutual food has a great influence on the survival rate of seedlings. This is the habit of grouper and it is difficult to change. However, the authors found that the feeding of chironomid larvae at the most severe stage of spotted grouper feeding on each other can make each other disabled. Food is reduced. Since this stage is mainly fed with copepods or frozen Artemia, the size of copepods is not suitable for the caliber of fish, and it is necessary to find some large foods; Frozen Artemia is a dead bait and cannot be fed all day long. After feeding the chironomid larvae, the fish can eat palatable feed at any time, and the amount of residual food is reduced accordingly. When the fish grows up to 5cm, the phenomenon of mutual gluttony naturally decreases.
7.3 With regard to the salinity test of nursery water, the spotted grouper developed to late larvae, and the salinity of nursery water can be gradually reduced to about 25, without adverse effects on the fish. On the other hand, nursery requires larger amounts of rotifers, copepods, and sometimes rotifers, copepods reproduce better under lower salinity conditions, or they are derived from lower salinity water bodies. If the biological feed derived from the lower salinity water body is fed to a nursery pond with a salinity of 30-33 ,, the bait creature sinks quickly and eventually dies. In this case, the salinity of the nursery water is gradually reduced, so that it can be adapted to the growth environment of the bio-feed and can achieve a better nursery effect.
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