Symptoms and Control Methods of Ciliate Disease in Mud Crab (Scylla serrata)
Ciliate Disease in Mud Crab (Scylla serrata)
Ciliate Disease in Mud Crab (Scylla serrata)
Cause: This disease is caused by ciliate parasites. There are many species of ciliates that parasitize the mud crab (Scylla serrata), the most common being Zoothamnium, Carchesium, and Epistylis. Each type of ciliate has a roughly similar structure, being bell-shaped or goblet-shaped, with a disc-shaped peristomial membrane at the anterior end bearing cilia along its margin, and a stalk at the posterior end that attaches to the eggs, larvae, juvenile crabs, and adult crabs of the mud crab. When they multiply in large numbers, they affect the normal activity of the larvae, causing reduced feeding, impaired respiration, and difficulty in molting and metamorphosis, and in severe cases can cause mass mortality of zoea larvae. Affected juvenile and adult crabs have many fuzzy, downy growths on the body surface, are sluggish in response, move slowly, and have difficulty breathing; when dissolved oxygen in the pond water is low, they often die. This disease is characterized by a long course and a high cumulative mortality rate. The main causes of the disease are excessive stocking density in ponds, excessive residual bait, severe pollution, and high organic matter content in the water, resulting in extreme eutrophication of the aquaculture pond water, which leads to massive reproduction of ciliates. Especially during the high-temperature period from July to September each year, large numbers of ciliates attach to the crab body, seriously affecting the normal growth and development of the mud crab.
Symptoms: In the early stage of the disease, yellow-green and brown fuzzy growths appear on the body surface, the crab moves slowly, and responds sluggishly to external stimuli. Under a microscope, ciliate protozoans such as Zoothamnium and Epistylis can be observed. In the middle and late stages of the disease, the crab body is covered with a thick layer of attachments, causing damage to the gill filaments and difficulty in breathing, followed by secondary bacterial infection, leading to reduced appetite or even refusal to feed, stunted growth and development, and a weakened constitution that makes molting difficult, with a mortality rate of about 20-30%.
Cause: This disease is caused by ciliate parasites. There are many species of ciliates that parasitize the mud crab (Scylla serrata), the most common being Zoothamnium, Carchesium, and Epistylis. Each type of ciliate has a roughly similar structure, being bell-shaped or goblet-shaped, with a disc-shaped peristomial membrane at the anterior end bearing cilia along its margin, and a stalk at the posterior end that attaches to the eggs, larvae, juvenile crabs, and adult crabs of the mud crab. When they multiply in large numbers, they affect the normal activity of the larvae, causing reduced feeding, impaired respiration, and difficulty in molting and metamorphosis, and in severe cases can cause mass mortality of zoea larvae. Affected juvenile and adult crabs have many fuzzy, downy growths on the body surface, are sluggish in response, move slowly, and have difficulty breathing; when dissolved oxygen in the pond water is low, they often die. This disease is characterized by a long course and a high cumulative mortality rate. The main causes of the disease are excessive stocking density in ponds, excessive residual bait, severe pollution, and high organic matter content in the water, resulting in extreme eutrophication of the aquaculture pond water, which leads to massive reproduction of ciliates. Especially during the high-temperature period from July to September each year, large numbers of ciliates attach to the crab body, seriously affecting the normal growth and development of the mud crab.
Symptoms: In the early stage of the disease, yellow-green and brown fuzzy growths appear on the body surface, the crab moves slowly, and responds sluggishly to external stimuli. Under a microscope, ciliate protozoans such as Zoothamnium and Epistylis can be observed. In the middle and late stages of the disease, the crab body is covered with a thick layer of attachments, causing damage to the gill filaments and difficulty in breathing, followed by secondary bacterial infection, leading to reduced appetite or even refusal to feed, stunted growth and development, and a weakened constitution that makes molting difficult, with a mortality rate of about 20-30%.