Goldfish with a rotten back is a common disease, usually caused by multiple factors, including water quality problems, pathogenic microorganism infections, parasite infestations, and fish body injuries. Here are the specific causes and solutions:
1. Water Quality Issues
- Cause: Poor water quality is one of the main reasons for goldfish having a rotten back. Excessively high ammonia levels in the water, infrequent water changes, or improper water change methods (such as directly using untreated tap water) can all harm the health of goldfish and lead to skin ulcers.
- Solution: Change the water regularly, controlling the amount of water changed each time to about one - quarter, and use tap water that has been left standing. Keep the water quality clean and avoid the accumulation of ammonia and other harmful substances.
2. Pathogenic Microorganism Infections
- Cause: Infections by bacteria, fungi, or viruses are common causes of goldfish having a rotten back. For example, water mold disease and fin - rot disease can both cause goldfish skin ulcers.
- Solution: Treat with appropriate medications, such as bathing in malachite green, methylene blue, or oxytetracycline. Consult a veterinarian or professional in severe cases.
3. Parasite Infections
- Cause: Infections by parasites (such as Ichthyophthirius multifiliis) can cause ulcers and red spots on the surface of goldfish, especially when the water temperature is too low or the temperature difference is too large.
- Solution: Raise the water temperature to 25 - 28°C and bathe with medications such as White Spot Remover for a week.
4. Fish Body Injuries
- Cause: Goldfish may injure themselves during transportation, mixed - species breeding, or collisions in the fish tank. If not treated in a timely manner, the wounds are prone to bacterial infections, leading to ulcers.
- Solution: Isolate the injured goldfish, keep the water quality clean, and avoid further infection of the wounds. Soak in low - concentration potassium permanganate if necessary.
5. Feeding Environment Issues
- Cause: Overcrowding, inadequate filtration systems in the fish tank, or inappropriate water temperatures can all increase the risk of goldfish getting sick and lead to rotten backs.
- Solution: Reduce the stocking density, improve the filtration system, and ensure stable water temperatures. Before adding new fish to the tank, acclimate them to the water temperature and quality to avoid sudden environmental changes.
Preventive Measures
- Regular Water Quality Checks: Use water quality testing tools to monitor indicators such as ammonia and nitrite.
- Proper Feeding: Choose high - quality feed and avoid overfeeding to prevent water quality deterioration.
- Isolate New Fish: Quarantine and observe new fish before adding them to the tank to prevent the introduction of pathogens.
By implementing the above measures, the problem of goldfish having a rotten back can be effectively prevented and treated, ensuring the healthy growth of goldfish.