News  Autumn underwater: How seasonal changes affect fish

Leaves are piling up and the nights are growing chilly, unmistakable signs that autumn has arrived. While the season’s changes are easy to spot on land, quieter transformations are happening in the ponds, lakes, and rivers across Massachusetts. Beneath the surface, freshwater fish are shifting their behavior in response to cooler water and shorter days. 

Seasonal changes in water temperature and oxygen levels have a powerful effect on freshwater fish. Because they’re cold-blooded, the surrounding water regulates their body temperature, metabolism, and activity. In general, warm water speeds up their metabolism, while cooler water slows it down. But despite the falling temperatures, many freshwater fish become more active in the fall. 

Signaled by the decrease in day length, fish begin feeding heavily to build up fat for the long winter. Feeding strategies used in the summer may also begin to shift. To conserve energy while still gaining calories, predators like largemouth bass stop chasing quick, small baitfish and favor larger prey for a bigger payoff. Bass, northern pike, and pickerel often gather around remaining weed beds, drop-offs, or currents to wait for an easy meal. 

As temperatures drop and aquatic plants die back, the water holds more oxygen and maintains steadier oxygen levels. This allows fish to feed actively in various areas of a waterbody throughout the day and night. Coldwater fish, like trout, are no longer confined to deeper waters and can spread out across a waterbody. Warmwater fish like bass, pickerel, crappie, and bluegill, spend time in shallower areas, especially late in the day when the water temperatures are higher. 

As you layer up and head out this fall, remember that the fish are making their own seasonal adjustments too. If you like to fish but have never thought of fall as prime fishing season—it’s time to reconsider! Equipped with the knowledge of these seasonal shifts in fish behavior, and these tips for fall fishing, you can take full advantage of one of the most rewarding times of year to cast a line.