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SPRING STRESS
By Myron Kebus, MS, DVM
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Spring is an exciting time for pondkeepers. The days are growing longer and we are anxious to get outside and enjoy our ponds. However, spring is also a very dangerous time: pond fish have been inactive for several months and are susceptible to a number of ailments associated with changing water temperatures. They need to be carefully watched and slowly reintroduced to active pond life.
Temperature is the most important thing to measure in the spring and should be monitored on a daily basis. The air temperature can rise and fall dramatically in a short time. Although daytime temperatures may be quite warm, nights can still be cold, which is has a significant effect on water temperature.
Smaller ponds are more vulnerable to drastic water temperature changes, but even large ponds can be affected by changing weather. Ideally, the water temperature should not vary more than three degrees in a given day, but this is hard to control without a heater. The greater the temperature fluctuation, the more stress the fish will experience.
As the air warms and the pond temperature rise, the metabolic rates of animals and plants also increase. Everything becomes more active: fish, disease carrying organisms, plants, and bacteria that handle biological waste. Unfortunately, they don't all perk up at the same rate. For instance, the immune system of the fish is slow to become fully functional, while disease-carrying bacteria become active very quickly. There is a lag period before the immune system is up to speed, and this is the time when fish may become infected. In water temperatures below 50 F, the fish's sluggish immune system is safe because parasites are inactive, too. As the water warms, however, parasites become active within hours.
The fish have just survived several months of limited activity and no food, living off reserves, yet when spring hits they are forced to deal with a demanding time of year. If the fish were adequately fed in the fall before feeding was stopped, they should be strong enough to survive this time.
As the water temperature warms, the fish will begin to graze, nibbling on plants and small aquatic insects. This is a good, natural way for them to reactivate their digestive systems. Once the temperature rises above 50 F, the fish can be fed a limited diet of easily digestible fish food or cereal.
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It is very important not to feed too early or overfeed, because the fish are not ready to digest a full diet in the spring. The same digestion problems food can cause in the fall and winter are still a danger in the spring. When the temperature reaches 55 F to 60 F, a small amount of low-protein food can be added to the diet. When temperatures rise above 60 F, fish can be fed commercial pellets and higher-protein foods.
Feeding too soon or overfeeding is dangerous not only to fish, but also to your pond. Nitrifying bacteria, which break down waste products, are slow to reactivate when the water temperature warms. Too much food too soon results in more metabolic waste than the pond is ready to process. This waste can harm the fish, damaging their gills, skin, and fins.
While spring is an important time to pay close attention to your fish's health, it is not a good time to handle fish or make any changes to their environment. They are dealing with changing temperatures and readjusting to active life, so they are already experiencing a significant amount of stress. Handling the fish, netting them, moving them, or changing the water causes more stress.
If you have kept fish inside for the winter and want to get them back outside in the pond, measure the indoor and outdoor temperatures daily. Wait until the temperatures match before moving the fish. Any immediate temperature change should be no more than three degrees.
Spring is also not a good time to introduce new fish to the pond. New fish may be arriving from a geographic region where the water is already warmer. A sudden move to a cooler pond is stressful and dangerous. While any drastic temperature change poses a threat, it is much worse for fish to experience an extreme warm-to-cool change than a cool-to-warm one.
If at all possible, wait until temperatures level off between 60 F and 78 F before moving or handling your fish and making water or other pond changes. While it may be hard to resist the urge to play with your fish when they awake from their winter's nap, these precautions will leave you with vigorous fish and a healthy pond to enjoy throughout the summer.
Reprinted with permission from
WATER GARDENING Magazine
January-February 2002
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