Age of Bass

When talking to anglers, fisheries biologists are often asked, "How fast do bass grow?" This is particularly true for big fish. An angler who catches a big bass wants to know, "How old is it?"

Fish can be aged by examining scales or various bones. Hard body parts grow as the fish grows, adding annual rings similar to the rings in trees. Because the growth in the diameter of the hard body parts is proportional to the growth in length of the fish, examination of these structures reveals not only the age of the fish but also its length at each birthday.

By examining a sample of bass, information can be obtained about the growth history of a lake’s bass population. Alabama Wildlife and Freshwater Fisheries Division biologists collect this type of information on a regular basis. Most of the fish examined are five years old or younger, but we have seen a few largemouth bass as old as 16.

Growth can vary greatly between individuals. Without examining scales or bones it is not possible to say exactly how old a particular fish might be, even within a single population. Growth is dependent on the abundance of the right size forage and its availability. Food availability varies seasonally, annually, between reservoirs, and even between locations within reservoirs. Knowing this, it is possible to make some general observations about bass growth. The following table shows the average growth of largemouth bass and spotted bass in Alabama reservoirs. 

A brief look at the table can reveal much about bass growth. First, note that growth in length is greatest in the first year and decreases each year thereafter. Old fish increase in length very little from year to year. This does not mean that they stop gaining weight. The relationship between length and weight for the first years of life is such that the longer a fish is, the more weight it gains for each inch its length increases. Second, bass need to be about three years old before they are large enough to interest most anglers. The fish many anglers call "yearlings" are actually two-year-old fish. True yearling bass are too small to be caught with most bass baits.

One growth aspect mentioned above that the table does not reveal is the variability between individuals. Fish of the same age, in the same population, can have quite different growth rates. For bass, there is usually a range of about four inches between the largest and smallest individuals of the same age. That is, although the average three-year-old largemouth bass is 13.3 inches long, some will be as small as 11 inches and others as large as 15 inches. That’s why we can’t tell how old a fish is without examining the scales or other hard parts. A 15-inch bass might be an average four-year-old, a fast growing three-year-old or a slow growing five-year-old. A big bass, say five pounds, might be anywhere between six and 16 years old.

Growth rate is an important aspect of the biology of bass and all other fish species, and it takes a careful examination of many fish to provide information of value to Division biologists. The average growth rate of fish in a population is one important factor in determining whether a size limit would improve fishing.

James J. McHugh

Former District IV Fisheries Supervisor

Montgomery, Alabama