Hard clam biology and culture
2018-04-17 14:00:40
Abstract The hard clam is widely distributed on the east coast of North America and is an important economic bivalve in the Atlantic coast states of the United States. This species has a wide adaptability to temperature and salinity and adapts to a variety of substrate life. In 2000, the United States introduced Dalian. Combining the preliminary research on artificial breeding and breeding after introduction, this article reviewed the biological characteristics of crustacean growth, reproduction, larval development, and ecological habits, and the culture of clamshell plankton larvae. Intermediate breeding and breeding techniques provide references for the development of aquaculture in China.
Hard clams (Mercenaria mercenaria Linnaeus, 1758), also known as small round bracts, northern curtain clams or American drapery. Originally distributed on the eastern coast of the United States, it is one of the major economic bivalves in the shallow seas and tidal flats of the Atlantic coast of the United States. Its nutritional and economic value is relatively high. Shells can also be used as raw materials for advanced crafts and decorations. Inhibit tumor growth. Hard clams are expensive, and they are almost the same price as Bao after shelling. Hard shell clams are one of the most important economic shellfish in New England and Mid-Atlantic states, New York, New Jersey and Virginia. In 1995, the total output value of the states in the northeastern United States was 37.4 million U.S. dollars. The total output value in 1998 was 41.775 million U.S. dollars. The United States attaches importance to hard-shelled clam farming, and each state has its own growth and breeding plan. China has a large area of ​​measurable beach areas and a large number of coastal shrimp ponds. For example, the use of clam-shelled beach aquaculture or mixed polyculture with prawns can effectively use our beach resources, improve the ecological conditions of shrimp aquaculture ponds, and improve the efficiency of pond culture. It is of great significance to reduce the risk of breeding, increase foreign exchange through exports, and solve labor employment.
1 The biology of hard clam
1.1 Classification Animal World Mollusca (Mollusca)
Lamellibranchia
Received date: 2002-06-02
From the order of Venezoida (Veneroida)
Veneridae
Scientific name: Mercenaria mefcenaria (Linnaeus, 1758) Common names: north quahog, hard clam, hardclam, hard shell clam, cherrystone, cherrystone, small curtain Littieneck).
1.2 Distribution and habits are widely distributed on the eastern coast of the United States. There are also a small number of artificially transplanted populations on the west coast of the United States. The northernmost limit of the distribution in the Americas is St. Lawrence Bay, Canada. There is also a small distribution of the Atlantic coast in the United Kingdom and France. The most important are New England and Florida.
Hard clams have the largest number of soft bottoms containing shells, and they also have distributions in sandy depressions, muddy sand and mud bottoms. A study by Peterson et al. showed that the density of 1-2 year old crustaceans (9/m2) is higher than the average density of nearby sand plover (1,6 animals/m2) in the North Carolina seaweed area. Far more, and hard clams in the distribution area of ​​big leaf algae are larger than those in sand. Hard clams have a lifespan of up to 40 years, and they basically stop at 15 years of growth.
1.3 Temperature and salinity tolerance studies have found that the optimal growth temperature is around 20°C, and growth stops above 31°C or below 9°C. Hard clams will enter a state similar to hibernation at 4°C. However, when the temperature drops to 0°C, it can survive. The trials introduced after the introduction of Dalian showed that the crustacean juveniles can tolerate a low temperature of -3°C for a longer period of time, and the juveniles that have sowed at the intertidal zone in the Zhuanghe Shicheng sea area of ​​northern Dalian can also survive winters. The larvae of hard shell larvae grow fastest at 25-30 °C, and the minimum temperature for larvae development is 12.5 °C. The tolerability of hard shell clams to salinity increases with age, but inversely proportional to temperature. When the salinity is low and the temperature is high, the survival rate decreases significantly. The normal development of the egg salinity range is 20-32.5. Only 1% of the fertilized eggs developed to the larval stage at over 35, and the eggs were not developed at less than 17.5. At the temperature of 22.5-36.5°C, the salinity of the larvae was the fastest when the salinity was 21-30, and the growth was stopped when the salinity was lower than 15. The mortality rate was high. Compared with the embryos, the tolerance of the planktonic larvae to temperature changes decreased in the later period, while the tolerance to low salinity increased. During shell larvae, salinity greater than 20 can develop into the young larval stage. Juveniles (1.8-3.6mm) will die when salinity falls below 15 for a long time. Older crustaceans are more tolerant of low salinity, but salinity below 20 is slower. Because mature clams can close shells, they can tolerate longer periods of low salt. Adults can survive for 4 to 5 weeks at salinity of 10 and can balance the osmotic pressure in vivo and in vitro. However, prolonged exposure to low-salinity conditions is not conducive to growth and reproduction. The lowest dissolved oxygen of normal embryo development is 0.5 mg/L; when 0.2 mg/L, 100% died; at 0.34 mg/L, it can only develop to larvae and cannot form shells. At 2.4 mg/L, the larvae grew slowly, and the suitable dissolved oxygen range was 4.2 mS/L or more.
1.4 The growth rate of growth varies with geography and season. Growth in the northern region only occurs when the water temperature approaches 20°C in summer, which is the optimum temperature for this species. In winter, when the water temperature drops below 5-6°C, growth stops completely. For example, hard clams grow rapidly in spring and autumn in North Carolina and Georgia, slow in the months of winter, and slowest in summer. Hard clams grow faster in Florida than in the north. Water temperature is the limiting factor for growth, but other factors (such as food density) also affect the growth rate. Studies have shown that high-density cultured hard-shelled clams (3875/m2) reach the same specifications longer than those used at moderate density (323/m2).
The growth of hard clams is affected by seawater movement and algae nutrition. The ideal condition for growth is a gentle flow plus appropriate algae density with 4 mg of dissolved oxygen.
Whether it is natural or artificially cultivated crustaceans, the differences in growth rates are influenced by genotypes or genetics. At the fastest growth rate, the hard shell meal can reach commercial specifications after 24-36 months. Individuals that decisively grow at 10-16 months can be twice as large as those who grow slowly. About 10% of any hard-shelled clam population is derived from the fastest-growing parents, so choosing a fast-growing individual will yield significant economic benefits. Obviously, removing slow growing individuals during the nursery process can significantly reduce production costs.
1.5 Breeding and larval development Many hard clams can be propagated in the first year of life, reproduce repeatedly throughout the life cycle, and no decline has been observed. Hard clams are hermaphrodites and generally male gonads become precocious. Ninety-eight percent of the young cubs are males at first. However, as age and size increase, the sex ratio changes. Nearly half of the males in the third year will become females. The highest frequency of spawning was found at 22-30 °C in water temperature. However, spawning in the Indian Lagoon generally occurs in autumn when the water temperature drops below 23°C.
Hard clams are between 70-90 μm in diameter and contain a layer of gelatinous egg membranes. After 12 hours, fertilized eggs can develop into tandem larvae. The shell is formed within 26-30 hours. After 8-12 hours of development to the stage of larval larvae. Face plate larvae are approximately 12 days old. When the larvae are attached, the length of the shell is 200-210um, which is known as larvae with feet. Disappearance of the face plate in the attachment process becomes a childish cultivation method. The shallow sea middle culture is still in the exploration stage.
3 To develop various methods for the development of hard clams, such as the development of tanks, the formation of runway-shaped basins, ponds, etc., but they have not been successful. There are many reasons for this, either because too much water is used, the cost of raising the bait is too high, the cost of breeding is too high, or because the physiological and ecological conditions of hard clams are not met and the growth is slow. The best cultivation method is tidal culture, which is also a universally applicable method. Tidal aquiculture has two points to make: one is to select a suitable substrate, and the other is to seed a suitable seed size. The size of the seed should be large enough (>8mm) so that the lesser predators cannot prey, and some protection facilities must be used to prevent the invasion of predators. The most important thing in the management of tidal aquiculture is to be able to observe the seed in time. Generally, when the hard shell clam shell reaches 50 cm or the shell width reaches 22 cm, 70% can be harvested. There are many ways to harvest. The commonly used method is to use various types of tweezers for artificial harvesting. There are many methods for mechanical harvesting, but they all use water to impact sand containing hard clams. After the sand is washed away, clams can be harvested. Harvesting options are more convenient at low tides.
Hard clams (Mercenaria mercenaria Linnaeus, 1758), also known as small round bracts, northern curtain clams or American drapery. Originally distributed on the eastern coast of the United States, it is one of the major economic bivalves in the shallow seas and tidal flats of the Atlantic coast of the United States. Its nutritional and economic value is relatively high. Shells can also be used as raw materials for advanced crafts and decorations. Inhibit tumor growth. Hard clams are expensive, and they are almost the same price as Bao after shelling. Hard shell clams are one of the most important economic shellfish in New England and Mid-Atlantic states, New York, New Jersey and Virginia. In 1995, the total output value of the states in the northeastern United States was 37.4 million U.S. dollars. The total output value in 1998 was 41.775 million U.S. dollars. The United States attaches importance to hard-shelled clam farming, and each state has its own growth and breeding plan. China has a large area of ​​measurable beach areas and a large number of coastal shrimp ponds. For example, the use of clam-shelled beach aquaculture or mixed polyculture with prawns can effectively use our beach resources, improve the ecological conditions of shrimp aquaculture ponds, and improve the efficiency of pond culture. It is of great significance to reduce the risk of breeding, increase foreign exchange through exports, and solve labor employment.
1 The biology of hard clam
1.1 Classification Animal World Mollusca (Mollusca)
Lamellibranchia
Received date: 2002-06-02
From the order of Venezoida (Veneroida)
Veneridae
Scientific name: Mercenaria mefcenaria (Linnaeus, 1758) Common names: north quahog, hard clam, hardclam, hard shell clam, cherrystone, cherrystone, small curtain Littieneck).
1.2 Distribution and habits are widely distributed on the eastern coast of the United States. There are also a small number of artificially transplanted populations on the west coast of the United States. The northernmost limit of the distribution in the Americas is St. Lawrence Bay, Canada. There is also a small distribution of the Atlantic coast in the United Kingdom and France. The most important are New England and Florida.
Hard clams have the largest number of soft bottoms containing shells, and they also have distributions in sandy depressions, muddy sand and mud bottoms. A study by Peterson et al. showed that the density of 1-2 year old crustaceans (9/m2) is higher than the average density of nearby sand plover (1,6 animals/m2) in the North Carolina seaweed area. Far more, and hard clams in the distribution area of ​​big leaf algae are larger than those in sand. Hard clams have a lifespan of up to 40 years, and they basically stop at 15 years of growth.
1.3 Temperature and salinity tolerance studies have found that the optimal growth temperature is around 20°C, and growth stops above 31°C or below 9°C. Hard clams will enter a state similar to hibernation at 4°C. However, when the temperature drops to 0°C, it can survive. The trials introduced after the introduction of Dalian showed that the crustacean juveniles can tolerate a low temperature of -3°C for a longer period of time, and the juveniles that have sowed at the intertidal zone in the Zhuanghe Shicheng sea area of ​​northern Dalian can also survive winters. The larvae of hard shell larvae grow fastest at 25-30 °C, and the minimum temperature for larvae development is 12.5 °C. The tolerability of hard shell clams to salinity increases with age, but inversely proportional to temperature. When the salinity is low and the temperature is high, the survival rate decreases significantly. The normal development of the egg salinity range is 20-32.5. Only 1% of the fertilized eggs developed to the larval stage at over 35, and the eggs were not developed at less than 17.5. At the temperature of 22.5-36.5°C, the salinity of the larvae was the fastest when the salinity was 21-30, and the growth was stopped when the salinity was lower than 15. The mortality rate was high. Compared with the embryos, the tolerance of the planktonic larvae to temperature changes decreased in the later period, while the tolerance to low salinity increased. During shell larvae, salinity greater than 20 can develop into the young larval stage. Juveniles (1.8-3.6mm) will die when salinity falls below 15 for a long time. Older crustaceans are more tolerant of low salinity, but salinity below 20 is slower. Because mature clams can close shells, they can tolerate longer periods of low salt. Adults can survive for 4 to 5 weeks at salinity of 10 and can balance the osmotic pressure in vivo and in vitro. However, prolonged exposure to low-salinity conditions is not conducive to growth and reproduction. The lowest dissolved oxygen of normal embryo development is 0.5 mg/L; when 0.2 mg/L, 100% died; at 0.34 mg/L, it can only develop to larvae and cannot form shells. At 2.4 mg/L, the larvae grew slowly, and the suitable dissolved oxygen range was 4.2 mS/L or more.
1.4 The growth rate of growth varies with geography and season. Growth in the northern region only occurs when the water temperature approaches 20°C in summer, which is the optimum temperature for this species. In winter, when the water temperature drops below 5-6°C, growth stops completely. For example, hard clams grow rapidly in spring and autumn in North Carolina and Georgia, slow in the months of winter, and slowest in summer. Hard clams grow faster in Florida than in the north. Water temperature is the limiting factor for growth, but other factors (such as food density) also affect the growth rate. Studies have shown that high-density cultured hard-shelled clams (3875/m2) reach the same specifications longer than those used at moderate density (323/m2).
The growth of hard clams is affected by seawater movement and algae nutrition. The ideal condition for growth is a gentle flow plus appropriate algae density with 4 mg of dissolved oxygen.
Whether it is natural or artificially cultivated crustaceans, the differences in growth rates are influenced by genotypes or genetics. At the fastest growth rate, the hard shell meal can reach commercial specifications after 24-36 months. Individuals that decisively grow at 10-16 months can be twice as large as those who grow slowly. About 10% of any hard-shelled clam population is derived from the fastest-growing parents, so choosing a fast-growing individual will yield significant economic benefits. Obviously, removing slow growing individuals during the nursery process can significantly reduce production costs.
1.5 Breeding and larval development Many hard clams can be propagated in the first year of life, reproduce repeatedly throughout the life cycle, and no decline has been observed. Hard clams are hermaphrodites and generally male gonads become precocious. Ninety-eight percent of the young cubs are males at first. However, as age and size increase, the sex ratio changes. Nearly half of the males in the third year will become females. The highest frequency of spawning was found at 22-30 °C in water temperature. However, spawning in the Indian Lagoon generally occurs in autumn when the water temperature drops below 23°C.
Hard clams are between 70-90 μm in diameter and contain a layer of gelatinous egg membranes. After 12 hours, fertilized eggs can develop into tandem larvae. The shell is formed within 26-30 hours. After 8-12 hours of development to the stage of larval larvae. Face plate larvae are approximately 12 days old. When the larvae are attached, the length of the shell is 200-210um, which is known as larvae with feet. Disappearance of the face plate in the attachment process becomes a childish cultivation method. The shallow sea middle culture is still in the exploration stage.
3 To develop various methods for the development of hard clams, such as the development of tanks, the formation of runway-shaped basins, ponds, etc., but they have not been successful. There are many reasons for this, either because too much water is used, the cost of raising the bait is too high, the cost of breeding is too high, or because the physiological and ecological conditions of hard clams are not met and the growth is slow. The best cultivation method is tidal culture, which is also a universally applicable method. Tidal aquiculture has two points to make: one is to select a suitable substrate, and the other is to seed a suitable seed size. The size of the seed should be large enough (>8mm) so that the lesser predators cannot prey, and some protection facilities must be used to prevent the invasion of predators. The most important thing in the management of tidal aquiculture is to be able to observe the seed in time. Generally, when the hard shell clam shell reaches 50 cm or the shell width reaches 22 cm, 70% can be harvested. There are many ways to harvest. The commonly used method is to use various types of tweezers for artificial harvesting. There are many methods for mechanical harvesting, but they all use water to impact sand containing hard clams. After the sand is washed away, clams can be harvested. Harvesting options are more convenient at low tides.