Fish have the weakest immune systems in the Fall and Spring so before closing the pond for the winter we would suggest monitoring the fish for any signs they may be sick and to take preventive measure to ensure they do not get sick.
Signs your fish may be sick: If you see your fish flashing, rubbing, see red sores (ulcers), or notice they are much less active than normal.
Treating sick fish: We would suggest treating for parasites and bacterial infections if your fish are exhibiting any of the signs listed above. There are an abundance of products on the market to treat your fish and we have a few favorites. Only one treatment should be done in a pond at a time so we recommend treating for parasites first. Most of the time when fish have signs of a bacterial infection it is because there is a parasite present. To treat all types of parasites would suggest Paracide Green. The treatment would entail 2-3 doses over a 7-14 day period depending on the severity of the fish. For bacterial infections we always recommend Medi-Koi, a medicated fish food. Feed your fish Medi-Koi exclusively for 10-14 days.
If your fish are not showing signs of being sick it does not mean you should take no action but rather treat with medications that will prevent them from becoming sick. Our favorite products for prevention are: Pimafix (Fungus), Melafix (Bacterial) and AquaPrazi (Flukes). Flukes are one of the most common parasites found in a water garden and they can often be compared to fleas on a dog or cat, always present but do not take control unless the immune system has been compromised.