fish die off?

Question

A big lake here in St. Louis, MO. is stocked by Natural Resource department. Trout and i don't know what. All the catfish have died in last few weeks od below freezing weather. Other lakes in area of same size and type have no die off. What are possible causes?

Answer 1

The same thing happens in ponds.
Oxygen depletion fish kills are most commonly caused by a die-off of the microscopic green plants (phytoplankton) in the pond, or overturns in which oxygen deficient water from the deeper levels of the pond mixes with water in the upper levels. Phytoplankton imparts a green color to the water in a properly fertilized pond. It is essential as part of the food chain and as a supplier of oxygen. A sudden die-off of these plants may occur, especially during periods of cloudy, overcast weather, when the plants use more oxygen than they supply to the pond. As the phytoplankton die and decompose, the remaining oxygen in the pond is consumed and within a short time, a fish kill occurs due to oxygen depletion.

To prevent oxygen shortages due to phytoplankton die-off, proper fertilization should be practiced. However, ponds should not be fertilized to the point where they become a “pea soup green,” with visibility of only two to three inches instead of the ideal 12 to 18 inches of visibility. A herbicide can be used to thin out phytoplankton growth when it becomes too dense. Caution should be used to prevent a fish kill. If oxygen depletion occurs, apply either triple superphosphate fertilizer at the rate of 17 pounds per acre, or liquid fish pond fertilizer at one gallon per acre to re-establish the phytoplankton.

Overturns can lead to oxygen depletion fish kills. During summer, water in a pond will become stratified (form layers), with warmer water in the upper level and the colder water near the pond bottom. This stratification is particularly severe in ponds with dense growths of blue-green or “scum” algae on the surface. The colder water may become oxygen-deficient due to interaction with certain elements in the pond bottom and lack of photosynthesis by phytoplankton at greater depths.

An overturning or mixing of this colder, oxygen-deficient water may occur after a heavy rainfall. If the rainfall is of sufficient quantity, it produces a mixing of the pond water as the cold rainwater sinks to the pond bottom. It displaces the oxygen-poor water, which mixes with the water in the upper levels of the pond. The result is a fish kill due to insufficient oxygen in the water.


Remedial measures for oxygen depletions in ponds can be any method that adds sufficient oxygen to the pond water to prevent or minimize a fish kill. A water pump can be used to pump fresh water into the pond, or the water in the pond can be sprayed into the air and allowed to fall back into the pond. This will oxygenate the water, however, it is important that water that is sprayed is water taken from near the surface and not stagnant bottom water. Any device that agitates and aerates the water sufficiently can be of value. Do no use well water as a source for pumping fresh water into the pond, as it can be very low in oxygen.

Pesticides cause a number of fish kills in ponds throughout Alabama each year. Convulsive, erratic swimming and lethargy are symptomatic of pesticide toxicity.


If an organo-phosphate insecticide is the cause, the pectoral fins of the fish will be reversed. The pectoral fins of a healthy fish point toward the tails, but the pectoral fins of a fish poisoned by insecticide curl up and point toward the head. Generally, the small fish will be killed first and eventually all sizes of fish may die.
Fish ponds should not be built in areas adjacent to crops that are likely to be treated with pesticides toxic to fish. Diversion ditches should be dug around the pond to prevent toxic runoff water from entering it.

Other major causes of fish kills in ponds are parasites and disease. Fish killed or weakened by parasites and/or disease may show visible external signs, such as lesions, hemorrhages or changes in pigmentation. The fish may be sluggish or swimming erratically.

A fish kill caused by parasites or disease will extend over a longer period of time, compared to a kill caused by oxygen depletion, when large numbers of fish are killed within a few hours. The fish kill may occur over a period of several days or even several weeks, with a few fish dying each day. The number of dead fish gradually increases until it peaks, and then decreases as the parasite or disease runs its course.

Swarming of the winged form of the fire ant in later winter or early spring has caused many fish kills. As the swarming ants fall into a pond, bluegills gorge themselves on the ants. If enough ants are eaten, the fish will die, but the majority of fish feeding on the ants will become ill and recover without lasting effects. Fire ant-caused fish kills do not present a serious problem by significantly reducing the fish population. If a fire ant kill is suspected, examination of the fish’s stomach will confirm the problem.

A new fish killing pathogen discovered.
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Answer 2

Over feeding The cloudy water is led to by micro organism growing to be on the uneaten foodstuff and in part damaged down foodstuff. those insects use truly some dissolved oxygen and many the fish would nicely be suffocating. Or the water chemistry has became poisonous. I advise that you regulate 20% of the water interior the tank once you could. provide up feeding the fish for some days. (they wont starve. Siphon the bottom acquarium muck out (it really is observed as mulm). do this quite a few circumstances. also, there would nicely be too many fish for the size of the tank and the quantity of water.The water ought to sparkling up in some days. If no longer substitute 25% extra of the water. (i.e depart seventy 5% of the unique water interior the tank on my own). verify if there's a community acquarium club close to you. they're tremendous human beings and would provide suggestion about fish density and the sorts of fish they advise on your acquarium set up, and suggestion on reliable water filter out set-up. Overfeeding is the most generic acquarists blunders. Dan the solutions-guy. more suitable factors favourite & not at all refused.

Answer 3

Probably low oxygen levels in the lake
this sometimes happens in low oxyengated lakes

this is typically called a FISH KILL