Pond owners often notice that fish do not behave the same way throughout the year, according to Scott Jones, small impoundment extension specialist for the University of Arkansas at Pine Bluff.
In spring and fall, fish may be active and easy to catch, while in mid-summer, they often feed early in the morning or late in the evening. During winter, fish can seem almost absent.
Jones said these seasonal changes are not random. One of the strongest drivers of fish activity, health and survival is water temperature.
“Unlike mammals, most fish do not regulate their internal body temperature,” he said. “Their body temperature matches the surrounding water, which means that nearly every internal process — digestion, movement, growth, immune response and oxygen demand — is influenced by temperature. As water warms or cools, fish metabolism speeds up or slows down accordingly. This makes fish highly efficient under ideal conditions, but it also means they are sensitive to temperature extremes.”
Jones said each fish species has a preferred temperature range where growth and performance are highest. For example, largemouth bass grow best in water temperatures near 80 degrees Fahrenheit, while rainbow trout perform best around 60 degrees. These temperature preferences help determine which species are suitable for stocking in a given region and why some species struggle outside their ideal range. When water temperatures move above or below these preferred conditions, fish experience metabolic stress that can affect growth, behavior and health.
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“Cold water presents several challenges for pond fish,” he said. “As temperatures drop, metabolism slows, and fish become less active. Feeding and digestion decline, reaction times slow and swimming strength decreases. While fish require less food during this time, the tradeoff is reduced ability to avoid predators and fight disease. Immune function can be compromised, especially when cold temperatures combine with other stressors.”
A common winter issue in Arkansas ponds is gradual channel catfish mortality. These losses often occur from December through February and may involve one or a few fish at a time over several weeks.
“Affected fish may appear thin, pale or develop fuzzy gray or brown patches on their skin or fins,” Jones said. “Channel catfish are particularly sensitive to cold water in ponds with low hardness. The combined stress of cold temperatures and poor water chemistry can weaken immune defenses, making fish more susceptible to fungal infections often referred to as ‘winter fungus’ or ‘winter kill.'”
Jones cautions landowners that warm water can be just as stressful as cold. As temperatures rise, fish metabolism increases, leading to higher activity levels, faster digestion, greater waste production and increased oxygen demand. At the same time, warm water holds less dissolved oxygen. Fish must work harder to meet their oxygen needs just as less oxygen is available.
“In deeper ponds, fish can find relief by moving into deeper, cooler water,” he said. “A complication with this strategy can emerge, as ponds often run out of dissolved oxygen in deep water during summer from a combination of poor circulation and oxygen-consuming organic decomposition on the pond bottom. In situations where livable deep water is not available, fish may instead seek shaded areas and reduce activity during the hottest parts of the day, becoming more active at night or during early morning and evening hours.”
Prolonged exposure to high temperatures can reduce growth, weaken immune systems and increase susceptibility to disease and predation. If temperatures continue to rise beyond what fish can tolerate, internal systems begin to fail, which can ultimately lead to mortality.
“Fish are rarely affected by a single stressor alone,” Jones said. “While a fish may tolerate slightly suboptimal temperatures, problems arise when multiple stressors occur at the same time. Poor nutrition, low dissolved oxygen, unfavorable water chemistry and temperature extremes can combine to overwhelm a fish’s ability to maintain internal balance. This is why pond owners may experience losses even when no single condition appears extreme.”
Jones said understanding how temperature affects fish helps pond owners make better management decisions year-round. Maintaining good water quality, avoiding unnecessary disturbances during periods of extreme heat or cold, and recognizing seasonal changes in fish behavior can all help reduce stress on pond fish. Healthy ponds give fish the energy reserves they need to withstand winter cold and summer heat, improving survival, growth and overall pond performance.
“By recognizing temperature as a central driver of fish health, pond owners can better anticipate seasonal challenges and take steps to keep their ponds productive and enjoyable throughout the year,” he said.
For more information about pond management, contact Jones at (870) 575-8185 or joness@uapb.edu, or contact your local county extension office.
Will Hehemann is an extension specialist of communications for the University of Arkansas at Pine Bluff School of Agriculture, Fisheries and Human Sciences.