CATDOLL : CATDOLL: What to do if the clam seedlings do not eat the food?

1. Choose a breeding environment

The breeding site of clam should be conveniently located, far from pollution sources, with calm wind and waves, smooth tide, flat terrain, dry exposure time of no more than 4 hours at low tide, stable bottom quality, and sand content of 70% to 90% in the middle and low tide areas, or ponds and beaches in the reclamation area with suitable bottom quality and water quality. The beach (or pond bottom) that has been cultivated for many years needs to be turned over and improved. After the mud and sand are washed by tides and exposed to the sun for many times, the beach surface is leveled, and harmful organisms and debris are picked up. The land that is easily eroded by floods and covered with mud and sand should be built with Miscanthus to prevent floods. The width of the embankment is 30 to 40 cm, and the embankment is 20 to 30 cm higher than the surface of the land to stabilize the surface and prevent the loss of seedlings.

For raising clams in ponds and beaches in the reclamation area, the dams and sluice gates should be repaired. The pond water should be drained one month before sowing the seedlings, and the bottom of the pond should be exposed to the sun for 15 to 20 days. 15 to 20 kg of bleaching powder with a chlorine content of 25% to 28% should be evenly sprayed throughout the pond for disinfection. After disinfection, the seawater should be filtered with a 0.25 mm mesh, and the water should be soaked for 2 to 3 days. The pond water should be drained and the soaking and drainage should be repeated 2 to 3 times. The water depth should be 30 to 50 cm after the pond is cleared. Every 2 to 3 days, 0.5 to 1 g of urea and 0.1 to 0.5 g of superphosphate should be used as the basic bait for cultivation per cubic meter to make the water light brown to facilitate the growth of clams.

The most suitable seawater temperature for the growth of clams is about 15℃～30℃. They start to grow when the water temperature reaches above 11℃ in spring, and stop growing when the water temperature drops below 10℃ in winter. The fastest growing period for clams in southern Zhejiang is from April to June and from September to November, and the growth rate is extremely slow from December to February of the following year. The growth rate of clams varies significantly with the size of the individual clams. The shell length and weight growth rate of smaller clams are much faster than that of larger clams. The water level of shrimp ponds for clams should be controlled at a depth of 30 to 50 cm on the beach.

2 Scientific breeding of seedlings

Clams are hermaphrodites and generally reach sexual maturity in two years. The gonads of sexually mature clams are distributed around the visceral mass and extend to the base of the foot. The female gonads are milky white, while the male gonads are light orange or creamy yellow. The sperm is narrow cocoon-shaped and about 3 microns long. The eggs are spherical, with a diameter of about 70 to 90 microns, and are covered with a layer of gelatinous egg membrane.

The breeding season of clams is in early summer, which varies with species and regions. The spawning period in Liaoning, Shandong and other places is from July to August; in Jiangsu, Zhejiang and Fujian, it is from June to July; in Guangdong and Guangxi, it is from May to July. The surface temperature of seawater during the spawning period of clams is about 27℃～29℃, and the suitable water temperature for embryonic development is 24.9℃～31.4℃, and 26℃～28℃ is the best; the suitable temperature for larval growth and metamorphosis is 24.9℃～31.0℃, and the suitable specific gravity range is similar to that of embryonic development; when the bait fed is fresh and of good quality, the young clams are large and metamorphosis is early. The sand content in the suitable survival environment for clam seedlings is at least 75, and all sand is best. The seedlings have strong adaptability to low-density seawater.

Cultivate the 0.5-1 mm clam seedlings into 50-70 optimal seedlings per 500 grams in stages. In the first stage, cultivate the 0.5-1 mm seedlings into 0.8-1.5 cm seedlings, sieve them and evenly disperse them to cultivate suitable medium seedlings of about 3 cm. The water depth on the beach of the cultivation pond is 15-30 cm to facilitate the rapid growth of benthic diatoms. The water level is appropriately raised as the water temperature rises. The pond water is preferably dark brown with a slight diatom.

3. Strengthen daily management

Seedlings can be sown according to different seed specifications. Small seedlings are generally sown in April and May, medium seedlings are sown from December to February and March of the following year, and large seedlings are sown before spawning, that is, in mid-to-late September. It is recommended to use wet sowing, also known as water sowing, to improve the quality and effect of sowing. After sowing, the distribution of seedlings should be checked in time. Those that are too dense should be dispersed, and those that are too sparse or have died locally should be supplemented. Small seedlings are generally sown in higher tide areas. After 6 to 7 months of cultivation, the individual size increases, the food intake increases, and the ability to resist enemies is enhanced. They should be moved to lower tide areas to accelerate growth. In summer, clam seedlings that are exposed to the scorching sun on higher ground should be moved to lower tide areas. In aquaculture areas that are susceptible to typhoons, floods, extreme heat, floating oil and other pollutants, preventive and rescue measures should be taken. Harvest early or move to safe sea areas for cultivation before the typhoon arrives. After the flood, the mud and sand covering the surface of the pond should be cleaned up in time, and scattered clams should be gathered to reduce losses.

During the cultivation period, frequent inspections should be conducted to promptly remove harmful predators. For fish, 5 to 8 kg of tea seed cakes can be crushed and soaked in water per mu, and then evenly sprinkled on the pond surface; crabs, snails and other predators can be removed with nets or by hand. When water is stored in the reclamation area to raise clams, the filter net should be strictly prevented from being damaged. Night lights can be used to trap fish, shrimps, crabs and other harmful predators in the water, or the pond water can be drained regularly to drive out and capture harmful predators. First, lower the water level to 20 to 30 cm, then sprinkle bleaching powder all over the pond, and after 6 to 10 hours, introduce filtered seawater to dilute it, then drain the water, and rinse it repeatedly with 2 to 3 tides.

When the water is stored in the reclamation area to raise clams, attention should be paid to the changes in water color. On sunny days, 0.5-1 gram of urea per cubic meter should be applied every 2-3 days to keep the water color light brown. If the water color becomes clear and the bait is insufficient, 1 gram of soybean milk per cubic meter can be fed as a substitute bait. After 1-2 years of cultivation, clams can be harvested when the shell is more than 3 cm long. Harvesting starts from March to April and ends before the clam breeding season in September.

4. Strengthen disease prevention and control

The high temperature in summer causes clams to die and rot, and then infect each other; thunderstorms or continuous heavy rains after exposure to the sun cause the gravity of seawater at the mouth of rivers to drop rapidly; the breeding density is too high, and the individuals are weak after breeding; the water quality and bottom sediment in the ponds of breeding farms are polluted, and there are parasitic diseases and other factors, which are important reasons for the death of clams. Every month, 10 kg of quicklime or 0.125 kg of chlorine dioxide can be used per acre to disinfect and sterilize the water to prevent diseases.

Clam seedlings are raised in summer when the water temperature is high, so disease prevention and control and prevention of harmful organisms are particularly important. The water used for seedlings must be treated by sedimentation, sand filtration, ultraviolet sterilization, or disinfected by spraying bleaching powder throughout the pond. During the cultivation process, 0.5 mg of oxytetracycline per liter is used to prevent and control diseases, which can inhibit the large-scale reproduction of seedlings and is beneficial to the development and growth of young clams. Therefore, during the cultivation of young clams and juvenile shellfish, 1 to 2 grams of antibiotics such as chloramphenicol, sulfamethoxazole, furazolidone, or oxytetracycline are added per cubic meter every day to inhibit bacterial reproduction. When there are polycystic ovary syndromes attached to the shell surface of the juvenile shellfish, 2 to 4 grams of furazolidone per cubic meter can be added to control the reproduction of polycystic ovary syndromes for a better effect; or 4 to 6 grams of penicillin or streptomycin can be sprayed per cubic meter in the bait pond to achieve good disease prevention results.

The suitable seedlings for clams are to cultivate the 0.5-1.0 mm clam seedlings into 50-70 pieces/500g of suitable seedlings in stages.