A Case Study on the Treatment of Eimeria Infection in Adult Carp

In early April 2005, a farmer came to my clinic for a consultation. The adult carp he was raising had recently stopped feeding and begun to die. The mortality was not high; in the early stage of the disease, one fish died every three to four days, and in recent days two to three fish died per day. The disease had been present for over a month. It had been treated as enteritis, with disinfectants applied by splash for 3 to 4 days and thiamphenicol given orally for 5 days, yet the dead fish did not decrease and the condition did not improve. The dead fish appeared dark in body color with a distended abdomen; when the abdomen was pressed by hand, a white purulent substance flowed out. To confirm the diagnosis without error, the farmer was instructed to go back and bring in samples of the diseased fish for laboratory examination.

Examination of the diseased fish: Visual inspection showed the diseased fish were emaciated, with dark body color, abundant mucus on the body surface, and mottled ulceration of the gill lamellae. When the abdominal cavity was opened, ascites was present, the intestinal tract was enlarged and thick, the intestinal wall was relatively thin, and the intestine was filled with white rice-grain-like cysts. Microscopic examination: smears were taken from the body surface mucus, gill lamellae, and white cysts and examined separately under the microscope: the mucus contained numerous Trichodina and Epistylis; the gill lamellae were severely ulcerated; under the microscope, many mature oocysts and trophozoites of Eimeria were visible, each oocyst containing four spores, and each spore containing two sporozoites arranged side by side in opposite orientation. Most sporozoites were banana-shaped. The pathogen was confirmed to be Eimeria infection complicated by Trichodina and Epistylis infections.

Treatment: On the first day, a potent antibacterial and antiparasitic agent was splashed over the entire pond, and after a one-day interval it was applied once more. Then 0.7 g/cubic meter of copper sulfate was splashed over the entire pond. At the same time, Bao Chong Qing was given orally for 5 to 7 days. For the first three days, because the fish fed little, the oral medication dose was calculated according to fish body weight, with less feed added, so as to get the fish to ingest as much medicated bait as possible. Three days later, a phone call was made to inquire about the condition, and the farmer said: after one round of splashing the medication, the fish began to feed the next day, and the amount eaten increased day by day, but there were still dead fish. The farmer was instructed to continue splashing and oral medication according to the prescription, and to change one-third of the water 24 hours after splashing the copper sulfate. Seven days later, the fish fed normally and no more dead fish appeared.

Because Eimeria infection is not a frequently occurring disease in carp farming, it is easy to miss during diagnosis and treatment, leading to misdiagnosis, delaying timely treatment of the diseased fish, delaying carp growth, lengthening the farming cycle, increasing farming costs, and bringing relatively large economic losses to farmers.