What are the causes of head-hole disease in fish?

Fish head-hole disease has two main causes: nutritional deficiency and internal protozoan parasitism. After infection, fish usually show body tremors, restlessness, and reduced appetite, with specifics varying by stage. Early: normal eating and active swimming with only occasional shivers. Mid: less food, more frequent tremors, reduced pale-yellow stool. Late: refuses food, slow swimming, rubs against the tank.

For head-hole disease from nutritional deficiency, improve it by supplementing nutrition. If it is from internal protozoan parasitism, promptly deworm the fish internally.