Koi are not indigenous to Canada, so in our northern ponds, much like their human owners, they survive winter but they don’t particularly flourish in it. Fish are cold-blooded creatures that cannot produce their own heat. Instead, isoenzymes are produced as needed to provide them with bodily functions such as the production of energy, regardless of temperature. As the water gradually warms up in the spring, these isoenzymes are no longer produced and regular enzyme systems begin to function.
Before the fish get “warm” in summer, there’s a small period of time where the water temperature has become too warm for the isoenzymes and too cold for the fish’s own immune system to function optimally. At the same time, parasitic and bacterial populations are proliferating at explosive rates – they like the cold water! This is when the fish are most prone to developing illnesses. Further compounding these difficulties, fish have usually not been fed all winter. Feeding koi in the springtime is important in rebuilding these energy stores and supporting their immune systems.
The first food in the springtime should be easily digestible. Wheat germ based foods like Aquascape Premium Cold Water Fish Food Pellets are popular, and for good reason. The fish like them and they are good “first foods” for the spring. Food should first be offered when the water temperature of your pond (not air temperature) reaches 10° C. Feeding should be sparing! If you load up the fish, they will load up the pond with fish wastes and the beneficial bacteria responsible for reducing the wastes will not be functioning optimally in cooler water. You can start with Aquascape Premium Cold Water Fish Food Pellets until the water reaches 15° C and then switch to any combination of two good quality summer foods. We recommend Aquascape Premium Color Enhancing Fish Food Pellets, Aquascape Premium Fish Food Flakes for smaller fish, and Aquascape Pond Fish Vitamin Treats.
Like any good parent, you don’t need to be a doctor to know when your aquatic “babies” are sick. As with human children, direct examination of your koi kids is important but can be much more difficult. You need to spend time, on a regular basis, observing your fish as they rest in your pond. Check for clamped fins, redness in the skin or fins, swollen eyes or lips, or fraying, rotting fins. Notice if any fish are on their own, away from their school. Look for white slimy patches on your fish. All of these symptoms could indicate that the combination of winter’s stress – no food, and possibly an opportunistic parasite or bacterial infection – is bearing down on your fish.
Water tests may be useful as elevated levels of ammonia and nitrogen can be toxic for aquatic life. Making sure the pond is as clean as possible, but not “scrubbed” will help bring the fish into springtime in the best possible health. We do not recommend draining a pond and scouring it until it’s sterile. Rocks, gravel, and a soft, light carpet of algae in the pond are all good things and contribute to the reduction of nitrogen and other fish wastes in the pond. In ponds that have balanced ecosystems with fish, plants, and plenty of space, the biological processes can take care of problems on its own. However, all riverbeds and ponds eventually turn into swamps or bogs as organic solids accumulate. This process happens in your pond, too!
It’s a good idea to clean your pond every year or so to keep sludge levels at a minimum and promote naturally balanced water chemistry. To fight a variety of parasites which may have gained an advantage over your fish through the winter, apply pond salt to your fish holding tanks during your spring cleanout. However, don’t put salt directly into your pond as it will kill your most precious plants. Medicated food is highly recommended for fish while in isolation tanks, as it contains safe but effective levels of antimicrobials to help fight infection in the fish during the springtime warm up, and when their immune system has not regained its full strength. If you have any concerns regarding the health of your fish this spring remember, our staff are always available to advise you when needed.