The small melon worm belongs to the protozoa phylum, ciliate, notch family, and small melon worm genus, mainly parasitic in the skin, fins, gills, head, mouth and eyes of fish, forming a small white dot-like sac, which is visible to the naked eye. When it is severe, the fish body can see small white spots, so small melon worm disease is also called white spot disease.
The adult eggs of the multi-seeded melon worm are round or spherical, and the whole body is densely covered with short and uniform cilia. There is a large horseshoe-shaped or sausage-shaped nucleus in the body. The larvae are ovate or oval in shape, with isolong cilia all over the body and a long, thick caudal hair at the posterior end. The larvae burrow into the epithelial cell layer or intergill tissue on the surface of the body, stimulating the proliferation of surrounding epithelial cells, thereby forming small vesicles.
There are two main ways of reproduction of small melon worms: one is that the insect body in the host tissue divides and reproduces, generally without equal division 3 to 4 times and is stopped; the other is that the adult worm leaves the fish body, swims in the water for a period of time, stops and rotates at the origin, and soon the body secretes a colorless transparent elastic sac, generally round or ovate, sinking on the bottom of the water or other solids.
Epidemiological characteristics of small melon insects: Small melon insects are suitable for breeding water temperature of 15 ~ 25 °C, popular in early spring, late autumn and winter. When the water temperature drops below 10 °C or rises above 28 °C, the small melon worms will stop developing.