Temperature fluctuations mean trouble in fish ponds

Louisiana fish ponds often have big losses during spring because changing temperatures make fish more susceptible to diseases, according to LSU AgCenter aquaculture specialist Greg Lutz.

“Cold temperatures during winter force fish into a state of slow motion in which they eat very little and their immune systems are suppressed,” explains Lutz. “When temperatures begin to increase in the spring, disease-causing organisms present in pond water can get the upper hand on fish that are in a weakened state.

“Stress caused by abrupt temperature fluctuations, such as many parts of Louisiana experienced in the past several weeks, often aggravates fish health problems by further suppressing immune functions,” continues the expert. “These factors make fish particularly susceptible to other forms of environmental stress during the springtime, especially low dissolved oxygen levels.”

Many Louisiana ponds experience partial fish die-offs during the spring because of a combination of disease and low oxygen levels, according to Lutz.

“Algae produce oxygen during the daylight as a byproduct of photosynthesis, and this is usually a major source of oxygen in fish ponds,” explains the specialist. “As pond water warms during the springtime and the amount of sunlight increases, algae die back. If this happens too rapidly, oxygen levels will drop for several days.

“This type of oxygen depletion may kill some fish directly or cause sufficient stress to weaken their immune systems,” continues Lutz. “In these cases, bacterial infections usually occur within the next several days to two weeks.”

Lutz says oxygen depletions are easy to recognize and can be reversed by mechanical aeration.

“Partial depletions can be recognized by fish hanging at the water surface during the early morning hours or a by loss of appetite and activity in ponds where fish are fed,” he explains. “Lethal oxygen depletions begin with similar symptoms; fish congregate at the pond surface, gulping for air. Emergency aeration will be most effective in smaller ponds, but the success of any aeration practice will depend on the severity of the oxygen depletion.”

According to Lutz, there is no guaranteed approach that will eliminate springtime fish losses to disease or oxygen problems, but keeping population and fertility levels low throughout the year will help minimize the chances of a fish kill in the spring.

“Overcrowding, overfeeding or overfertilizing almost always compounds these problems,” the LSU AgCenter specialist explains, adding, “If pond owners don't thin out their fish through a regular management program, Mother Nature may take the opportunity to do it for them.”

For tips on all aspects of pond management, check out the LSU AgCenter's list of topics on management of recreational and farm ponds in Louisiana on its Website located at www.lsuagcenter.com/farmponds/ponds.html.

Cristina Rocha writes for the LSU AgCenter.

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