1. fin injury: the fin is hit or damaged by a foreign object, which causes the fin not to unfold normally. The treatment method is to put the fish in clean water, provide good water quality and suitable temperature, and let the fins repair themselves.
2. Infection or disease: When the fin is infected with bacteria, parasites or other diseases, the fin may not unfold normally. The treatment method is to put the fish in an isolation tank, use appropriate drugs for treatment, improve the water quality and provide a suitable feeding environment.
3. Malnutrition: When the fish lacks some important nutrients, the fins may not grow and unfold normally. The treatment is to provide a balanced feed, which contains a proper amount of protein, vitamins and minerals.
4. fin deformity: some fish are born with fin deformity and cannot be fully unfolded. This situation can't be cured, so we can only choose healthy fish to feed.