Clam

Clam, also known as variegated clam, is a shellfish. It belongs to the family Clamidae. Its scientific name is Ruditapes philippinarum. It is commonly known as Huage in the south. , Liaoning calls clam (xianzi), Shandong calls clam (gala), Japanese name: アサリ[あさり]Asari, English name: short necked clam. Clams are widely distributed in the North and South Seas of my country. They grow rapidly, have a short breeding cycle, are highly adaptable (wide temperature, wide salt, wide distribution), and have a long survival time out of water. They are an excellent shellfish suitable for artificial high-density farming. , is one of the four major cultured shellfish in my country.

Morphological characteristics

The shell is small, thin, and oblong. The top of the shell is slightly protruding and slightly curved forward in front of the dorsal edge. The radial ribs are fine and dense, and the ones located at the front and back are thicker, intertwined with concentric growth chakras to form a cloth pattern. The color and pattern of the shell surface vary greatly, including spots or patterns composed of brown, dark brown, dense brown or russet. The inner surface of the shell is light gray or flesh red, with 2 to 3 light-colored bands from the top of the shell to the ventral surface.

Living Habits

(1) Habitat Environment

Clams mostly live in the inner bays with less wind and waves, and in the mid- and low-tide areas where there is an appropriate amount of fresh water. , but are occasionally found on coastal islands with higher salinity and subtidal zones several meters deep; the habitat substrate is mostly sand mudflats with a sand content of 70% to 80%. Although they are also found in mudflats with very little sand and sand or gravel areas with very little mud, the number is very small.

(2) Lifestyle

Clams use their well-developed axe to dig sand and mud to live in caves. When the tide is high, it rises to the beach and stretches out its water pipe to carry out activities such as breathing, feeding and excretion; after the dry tide or when encountering external stimulation, the double shells are tightly closed, or it relies on the telescopic activities of the feet to return to the bottom of the cave and rest on the beach. Leave two holes formed by the outlet and inlet pipes close together.

The burrowing depth of clams varies with their individual size, substrate composition and season. Small individuals, those with softer substrate, or during seasons with higher water temperatures, will burrow shallower; while larger individuals, those with harder substrate, or during colder winters, will dive deeper. But generally speaking, the depth of cave dwellings is generally about 3 to 15 centimeters.

(3) Requirements for water quality

1. Water temperature: Clam is a wide-temperature shellfish. In natural sea areas, the water temperature ranges from 0 to 36°C, and it can adapt. When the water temperature is 5~35℃, the growth is normal, and the fastest growth is at 18~30℃. The upper temperature limit of clams is 43℃. When the water temperature rises to 44℃, the mortality rate reaches 50%. When the water temperature rises to 45℃, all clams die. When the water temperature drops to 0℃, the gill cilia stop. Movement and feeding stop; when the water temperature drops to minus 2 to 3°C, the mortality rate reaches 10% after 3 weeks.

2. Salinity: Clams also have strong adaptability to changes in the specific gravity of seawater. When the specific gravity is 1.004 to 1.027, life is normal, and the growth is best when the specific gravity is 1.015 to 1.020. In the inner bay breeding area near the estuary without flood control embankments, clams often die in large numbers due to flash floods. This is not only because of the sharp drop in the specific gravity of seawater, but more importantly because the floods bring a large amount of mud and sand. This causes the seawater to remain turbid for a long time, affecting the clams' breathing and feeding.

3. Dissolved oxygen: Clams can live normally in seawater with a dissolved oxygen of 1 mg/L. Therefore, the dissolved oxygen content of normal seawater can meet the living needs of clams. However, if the seawater is seriously polluted and the dissolved oxygen content remains below 0.5 mg/L for about 10 days, the clams will die.

4. Drought tolerance: Clams living in the intertidal zone have strong drought tolerance. The drying out time is related to the size of the individual clam, the temperature and whether it is ventilated