Living habits of big-eyed larvae of river crab

Living habits of big-eyed larvae of river crab

The larva gets its name because a pair of larger compound eyes are born at the end of the long eye stalk and are exposed outside the eye socket. Great changes have taken place in the internal organs and external morphology of bigeye larvae compared with oyster larvae, resulting in great changes in their living habits.

1. The big-eyed juvenile has developed swimming limbs, so the swimming speed is very fast. Due to the development of the balance sac, the body can be balanced to swim in a straight line. The big-eyed larva has more developed large claws and feet than the larva, so it has a strong ability to climb and climb, not only at the bottom of the water, but also on the stems and leaves of aquatic plants. The hook-like setae at the end of the foot is often used to hook and hang in places such as water plants and beach sand without being washed away by the current.

2. The big-eyed larvae already have gills and Gill cavities, so they can live out of water for a short time, so they are often attached to aquatic plants and pond walls, so that they will not die after leaving the water. Therefore, most of the crab seedlings are transported by dry method. Bigeye larvae have stronger ability to regulate osmotic pressure in vivo and adapt to freshwater life, so they show an obvious tendency of desalination. Groups of big-eyed larvae in the estuarine waters enter the rivers with the tide, forming a crab seedling flood.

3. The morphology of bigeye larvae is a transitional stage between larvae and young crabs, and the subsequent stage of juvenile crabs is suitable for living in freshwater shoals, so bigeye larvae show the habit of moving to shallow water areas. under natural conditions, it is often clustered in the shallow water areas along the banks of rivers and lakes.

4. The feeding habits of bigeye larvae are more extensive than that of zoea larvae. It can not only filter small plankton in water, but also prey on larger zooplankton, such as freshwater cladocera and copepod. Because of its powerful predator-chelate, it can easily catch Artemia and other foods several times its own volume when swimming or at rest. Bigeye larvae have the same habit of preying on weaker individuals of the same kind as oyster larvae, while bigeye larvae are ferocious, agile and have strong predation ability, so it is easier to catch oyster larvae or weak bigeye larvae as food. How to prevent bigeye larvae from preying on the same kind is a technical measure that should be paid attention to to improve the survival rate of seedlings. Bigeye larvae are omnivorous, not only like animal bait, but also take aquatic plants and commercial bait and so on.

5. The big-eyed larvae have stronger phototaxis than the zoea larvae, and they all like to move on the water surface except direct light. At night, light can be used to induce it to be dense. When the big-eyed larva develops into a young crab, it does not show this phototaxis, so it is necessary to use the phototaxis of the big-eyed larva to capture from the nursery pond when harvesting, because it is difficult to harvest in clusters at the young crab stage.