With a lot of practice, this method of aging can be very accurate but is not always definitive. Since Texas has very mild winters, it can be challenging to see these annuli as fish often still exhibit some growth through the winter. The annuli present on the scale allow us to count the number of winters (slow growth) the fish has been alive. The circuli widen back during periods of rapid growth, usually associated with the warmer season (Figure 2). Typically, this slow growth is associated with winter. But instead of counting each ring, like on a tree, we count “Annuli.” Annuli are formed by a tight grouping of “circuli” (individual rings) and indicate a period of slow growth. Reading a fish scale is similar to counting tree rings. We often choose to use scales to determine the age of a fish over more definitively accurate methods simply because taking a few scales from a fish does not harm the fish, and they will regenerate the missing scales. Circuli is each band/ring, and Annuli are formed by many circuli packed close together by a period of slow growth. Using Scales to Age Fish Figure 2: Fish Scale Diagram, Radii are the ridges extending from the focus to the edge of the scale. Having the secondary metric of age to reference draws a more detailed “picture” of the population condition and allows us to create a better management plan. In many instances, relative weights can be inflated by recent meals or spawning season (females), making the fish seem more closely related to the national average for its size class. Knowing the age allowed me to realize and address an issue that I would not have been able to see by just analyzing relative weights. A five-year-old bass should realistically be around 5-6 pounds. In a pond setting, bass can put on around 1 pound per year of weight. The bass referenced had a relative weight of 93%, which is very good, but the fish was five years old. One example of this would be a fish I surveyed last year that was 15.5” and weighed 1.9 pounds (Figure 1). We draw these comparisons in addition to calculating the relative weights of each fish because it is possible for a fish to be within the desired relative weight percentage but be much older than it should be. We often compare the estimated age and current size of the fish against the expected size for a fish of the same age-based upon species-specific growth rates. We age fish to understand the condition of the fish in your lake or pond. We use these scales to estimate the age of the fish, which gives us a better understanding of what is going on in your lake or pond’s ecosystem, Why age fish? Figure 1: Scale from a fish captured during electrofishing. In addition to environmental measurements, you may also see us collecting a few scales from each fish. We use length and weight data of the targeted species of fish to calculate the relative weights of the fish we record.
While conducting our electrofishing surveys, we collect many different metrics of data.
Whenever possible, we use fish scales to determine age because doing so doesn't harm the fish. To ensure your fish are achieving their optimal annual growth potential, when we conduct a survey, we gather a complete set of data, including the age of the fish.
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