1. Disease or infection: Zebrafish may be infected by bacteria, parasites or other pathogens. These pathogens can affect the health of fish, causing discomfort and abnormal behavior, such as lying on one's side. Common diseases include bacterial infection, fungal infection, parasitic infection and so on. If zebrafish lie on their side with other symptoms, such as loss of appetite, abnormal breathing or skin changes, disease diagnosis and treatment may be needed.

2. Water quality: Water quality is one of the key factors for zebrafish health. Unsuitable water quality conditions may lead to zebrafish lying on their sides. Too high or too low temperature, unstable pH value, high concentration of ammonia nitrogen or nitrite and other problems will have a negative impact on the physiological function of fish. Regular testing of water quality indicators, necessary adjustments and partial water replacement can help improve water quality and reduce the risk of abnormal behavior of zebrafish.

3. Stress and environmental problems: Zebrafish are sensitive to environmental changes and stress. Sudden environmental changes, too strong or too weak water flow, overcrowding or lack of proper shelter and swimming space may cause zebrafish to feel uncomfortable and stressed. When providing a suitable feeding environment, it is necessary to ensure that there is enough swimming space, suitable water flow and temperature, and appropriate hidden places to help relieve stress and provide comfortable living conditions.

4. Dietary problems: Improper feeding may also lead to zebrafish lying on their sides. Zebrafish is an omnivorous fish, which needs to provide diversified food and control proper feed. Overfeeding, lack of nutrition or unbalanced diet may affect the health status of fish and lead to abnormal behavior.