For the owner of a pond or lake, there is nothing more terrible than having a sudden mass extinction of aquatic life, also known as a Fish Kill.

Fish deaths come in many shapes and forms: sometimes large fish die, sometimes small fish die, other times all fish suffer the same disappearance. Some fish kills are limited to particularly sensitive fish species, others do not discriminate and affect all fish (including larger fish that continue to fish).

The death of a fish can be as small as 10-20 fish or as large as 10-20,000, and once the fish begin to die, it is usually too late to remedy the situation. The only way to thwart the phenomenon of fish kills is prevention. Before we can prevent fish kills, we must understand the six possible causes behind them:

1. Oxygen depletion

Oxygen depletion is the most common cause of fish death. Oxygen must be present in the water for fish to breathe; An oxygen level of 4 to 5 parts per million is recommended for healthy fish.

When oxygen levels drop to 2-3 ppm, the fish become stressed. Fish swimming close to the surface, sometimes gulping air, is a common symptom of this stage.

Large fish are the first to die in an oxygen depletion death, followed by smaller fish. Fish kills of this type often occur overnight or early in the morning, and generally occur within hours.

2. Extinction of large plants or algae

When a body of water filled with plants and algae suddenly receives less sunlight or receives algaecides and herbicides, major deaths can occur. The resulting decomposing matter pushes oxygen out of the water, suffocating the fish.

As a general rule of thumb, if your pond has more than 20% surface algae or plant cover, avoid algaecides and herbicides and get oxygen into the water as quickly as possible (see solutions).

3. Rotation

Stagnant water tends to migrate to different layers, like a layer cake. Fish typically reside in layers near the surface, where they enjoy warmer water and more dissolved oxygen.

The layer at the bottom is like a no man’s land fish in that it is generally cooler, has little or no oxygen, and is full of accumulated toxic gases that are trapped by layer differences.

In the spring and fall (and sometimes more often if the weather conditions are right), these layers mix, sucking all the oxygen out of the water and introducing toxic gases to the fish. If severe enough, the replacement can easily cause massive fish kills.

4. Surface freezing

When the surface freezes, the ice acts as the difference in temperature mentioned in n. ° 3. Gases poisonous to fish accumulate and can sometimes kill entire populations.

5. Toxins and chemicals

If pesticides or other harmful chemicals get into your pond, they can obviously have a damaging effect on any life in it.

Sometimes the application of herbicides or algaecides can cause fish kills, as the chemicals are lethal to all types of aquatic life.

6. Disease

The disease affects all forms of life at some point and is difficult to prevent. However, symptoms of the disease are usually less severe than most fish kills and occur gradually over time (rather than over the course of a few hours, like normal fish kills).

Diseases generally affect only one species of fish, rarely kill all of them, and rarely occur on a scale of mass fish kill.

Solution

– Add oxygen to the water keeping the water fresh and the fish happy

– Blend the layers to expand fish habitat and break down toxic gases

– Avoid excess algae to take control and absorb oxygen

– Avoid applying chemicals that can harm fish