Meloniasis is also known as white spot disease. [The causative agent is a small ciliate of the family Aphanizomenonidae, the genus Aphanizomenon, and the multinucleate Aphanizomenon. This is a group of ciliates that are relatively large in size. Its morphology differs greatly between the larval and adult stages. The larvae of the small melon worm infest the skin and gills of the fish, with the skin being particularly prevalent. When the larvae infect the host, they burrow into the epithelial tissue of the skin or gills, encasing their bodies in small cystic cells secreted by the host, where they grow and develop into adult worms. Adult worms break through the cysts and fall into the water, swim freely for a period of time and then fall to the bottom of the water column, stationary, secretion of a layer of gelatinous cysts. The worms in the cysts divide and multiply, producing hundreds or even thousands of ciliated larvae. The larvae come out and swim freely in the water in search of a host, which is the infective stage of the cucumber worm. The larva infects a new host and begins its life history again. [Symptoms Cases of ornamental fish suffering from Cucurbit parasitism are relatively common. At the initial stage of infection, there are white spots on the chest, back, caudal fin and surface skin of the fish, at this time, the fish feed as usual, after a few days, the white spots are all over the body, the fish lose the ability to move, often in a stagnant state, floating on the surface of the water, slow to swim, lack of appetite, emaciation, skin with hemorrhagic dots, and sometimes left and right, and in the aquarium wall, water plants, gravel, and the side of the side of the body quickly swim rubbing itchy, swimming and gradually lose balance. The course of the disease is generally 5 to 10 days. Infection speed is extremely fast, if the treatment is not timely, a large number of deaths can be caused in a short period of time. The suitable water temperature of small melon worm is 15～25℃. This disease mostly occurs in early winter, late spring and rainy season, especially in the lack of light, low temperature, lack of live bait is easy to epidemic. When the water temperature rises to 28℃, the small melon worm will start to die. [Prevention and control methods Adopting the weakness of the small melon worm that does not tolerate high temperatures, raising the water temperature, and then equipped with medication, usually the cure rate can reach more than 90%. If the treatment is timely, the cure rate can reach 100%. With 0.05 parts per million (0.05ppm) of malachite green and 25 parts per million (25ppm) of formaldehyde solution mixed treatment, the efficacy is better; can also be used to 1% saline immersion for a few days, or two parts per million (2ppm) of the methyl blue solution, immersed for 6 hours a day; or 28 ~ 30 ℃ two parts per million (2ppm) of the solution of quinine hydrochloride soaked for 3 to 5 days, or two parts per million (2ppm) of the solution of quinine hydrochloride, or one hundred thousand Two parts per million (2ppm) of mercury nitrite solution immersed in 30 minutes; or with fifty to seventy parts per million (50 to 70ppm) concentration of red mercury solution immersed in 5 to 15 minutes, or with 0.1 to 0.2 parts per million (0.1 to 0.2ppm) of mercury nitrate solution splashing, can achieve good results.