There are many reasons why fish become stressed and get sick or die.
Some factors include: rapid temperature changes, thunderstorms, acid rain, predation, breeding, overstocking, low oxygen levels, lawn and weed spraying, poor water quality, inadequate filtration, inadequate water circulation, parasites and disease, and very hot weather.
It is important to know that most parasites and bacteria that can cause disease in fish are present in your pond all the time, but generally there is a healthy balance in the ecosystem that keeps the fish healthy. Once the balance is disturbed, such as when fish health is compromised by increased stress, the disease organisms can overwhelm the fish and an outbreak of disease can occur.
Fish do not like temperature fluctuations of more than two degrees. When water temperature changes rapidly, it negatively affects the pH (alkalinity or acidity) of the water. Dramatic temperature fluctuations also cause fish to reproduce! Female fish release a pheromone into the water that drives males crazy and causes them to reproduce. This frenzy of activity can last 24-36 hours. Female fish can be chased, pushed, and shoved to death. Look for the scales on their sides to turn white and, in extreme cases, to be missing altogether.
Male fish are so exhausted from incessant chasing and breeding that they too suffer severe stress and may even die. Spawning fish are easy targets for predators. They are impervious to predators because they are so fixated on reproduction. Raccoons and blue herons are easy prey for the exhausted fish after spawning.
Electrical storms drop the barometer significantly, and all waters are robbed of their precious oxygen. Rain brings pollution and acidity to ponds, and when it falls torrentially, excessive amounts of both are poured into the ponds.
Another common mistake is to overstock the pond with fish. Remember that stocking density for goldfish should be about 1 inch of fish per 1 square foot of water surface. Koi require 250 gallons of well-filtered water each. In heavily stocked or overstocked ponds, good filtration and water circulation is essential. A pond full of algae is always low in oxygen, especially in the summer, so add an air pump to your pond system.
Summer is also the time for lawn care, and it’s not uncommon to have a neighbor who is obsessed with lawn care. Armed with pesticides and lawn sprays, they pose a danger to your fish and plants!
When these highly toxic chemicals are sprayed on lawns, the wind often picks up the drift and carries it off on ponds (up to 1 mile away). Unsuspecting pond owners lose entire fish populations within days of spraying the lawn (depending on the chemical analysis of the herbicide/pesticide).
Stress symptoms may not appear in fish until 14-21 days after a stressful period.
Costia and fluke are among the most common parasitic diseases in pond fish. Costia is a very small protozoan parasite that can cause massive mortality in a short period of time. Fish infested with Costia typically scratch at solid objects in the pond, become grayish and very lethargic, and you’ll notice an increase in foam on the pond surface. Leeches aren’t as aggressive, but many of the clinical signs seen in Costia can occur here as well. The mortality rate is usually much lower, but if left untreated, the fish can also perish from it.
The most common internal fish disease is ulcerative bacteremia caused by Aeromonas hydrophila. The bacterium is found throughout the fish and is carried into the bloodstream. Although mortality is usually not rapid, fish will die if not treated. Most outbreaks can be controlled with common antibiotics, but resistant strains have been observed if used improperly. It’s extremely important to use antibiotics judiciously to minimize resistance. When selecting a regimen, make sure it meets the appropriate labeling. This may be an injection treatment or a medicated feed.
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