By Dr. Hal Schramm

I read a lot of articles that talk about metabolism, and it’s usually in a rather negative sense—bass won’t chase fast-moving baits in the winter because their metabolism is slow, or bass don’t feed often in cold water because their metabolism is slow.

Have you ever heard about a time when metabolism was credited for a hot bite? Something along the lines of, “Dude, I really whacked ‘em today. Their metabolism must have been skyrocketing.”

Before exploring bass metabolism, let’s define it.

“Metabolism is the chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated.”
In application, that definition boils down this: Staying alive requires energy, and metabolism produces and uses energy. Understanding a bass’ metabolism and energy budget can help you put fish in the boat. And, it can help you keep them alive after you catch them.

Some simple truths about metabolism:
•    Metabolism increases with temperature up to near bass’ lethal temperature (about 98 °F). Bass are cold blooded—their body temperature is about the same as the water temperature—so their metabolism is higher in warm water.
•    Metabolism increases with activity. Bass chasing food or fighting the drag of your baitcaster have a higher metabolism than a bass at rest.
•    Metabolism requires oxygen. A bass with elevated metabolism needs more oxygen.

Let’s put this together to make some predictions about bass behavior.

Popular lore is that bass feed when their stomach is empty, and they don’t feed much in the winter because digestion slows. Partly true. Digestion slows in cold water because digestion is largely a chemical process (all chemical reactions are affected by temperature), but food in the stomach has little to do with feeding or, more specifically, hunger. Hunger—the actual (physiological) need for food that triggers feeding—happens when concentrations of circulating energy compounds, usually sugars or fats, drop below a threshold or set point -- sort of a like a biological thermostat.
The faster a bass burns energy (that is, the higher the metabolism), the sooner the energy levels drop below the threshold, and the sooner the bass is again hungry and looking for a meal. A bass living in 80-degree water has a higher metabolism, burns energy faster, and will eat more than a bass in 60-degree water. But be careful—eat more does not necessarily mean eat more often; it could mean get more energy by eating bigger energy packets. Summer is a time to think big baits first, downsize only if necessary.

So how does metabolism account for the bite slowing in the heat of the summer and then revving up again in the fall? I don’t think it’s all about metabolism, and I’ll give you some thoughts to ponder.

First, what summer slow-down? Bass bite all day long in mid-summer in Michigan and Minnesota. But yes, many Southern anglers agree the bite dwindles when the water temp is above the mid 80s and bass’ optimum temperature of 80 to 84 degrees. However, you’re reading surface temperature; bass are in cooler water if they can find it. Also, largemouth bass in the lab feed heavily when water temperature is in the mid to upper 80s. And, for a last point, activity raises metabolism and burns energy. A less-active bass burns less energy and will feed less.

Telemetry studies show bass move less in the summer. In some lakes it’s because the bass are hunkered down in the thermocline for heat relief; in all lakes, the forage is at its annual peak abundance and the bass doesn’t need to burn much energy to capture it. Nevertheless, the warmer the water the higher the metabolism and the more energy bass are trying to consume. The bass are feeding; they’re just harder to catch, or maybe harder to find.

Resting or inactivity is a way to conserve energy. Several bass movement studies indicate that bass have resting areas and feeding areas. One study in Lake Seminole that straddles the Florida-Georgia line found that bass moved from offshore standing timber to near shore vegetation at times that would coincide with feeding peaks. Expect more bass in feeding areas when metabolism is high (summer); expect more bass in resting areas when metabolism is low (winter). Also, bass in the feeding areas were more active. You may need a slower, in-your-face approach when fishing resting areas.

Bass can adjust their buoyancy and remain suspended without activity -- energy conservation in action. Suspending off structure or in deeper, dimly lit water may be the equivalent of a resting area. In the summer, the cooler thermocline can be the ideal resting area. If so, expect these bass to be less feeding oriented and possibly require a different presentation, maybe like a big, slow-moving Money Minnow or a Yumbrella rigged with match-the-hatch-size grubs, Money Minnows, or Mud Minnows.
Understanding bass metabolism will help you keep bass alive and healthy in the ‘well. Good for the resource, and good for cashing that check. But like a D-back that intercepted a pass and ran it back 40 yards, that bass you just caught probably has a high metabolism and an oxygen debt and needs a lot of oxygen.

Keep your livewell well aerated. In warm water, bass have higher metabolism and need more oxygen. Cool water holds more oxygen, and cooler bass use less oxygen. When water temperatures climb, add ice to cool your livewell. Half gallon milk bottles filled with water and frozen are perfect. But don’t overdo it. The following table gives you desirable livewell temperatures. You will not only weigh in more live bass, you will increase their survival after release. Try it. You will quickly see that bass from your cool livewell water are more vigorous and have a healthy slime coat compared to limp, dry-feeling bass from your buddy’s livewell with water temperature above 85 degrees.