Dating and Aging Trophy Largemouth Bass


Most bass anglers would agree the qualification criterion for a true trophy largemouth bass is 10 pounds. Why is it bass anglers are obsessed with catching a bass meeting or exceeding this weight?

Ten-pounds is the mark we all strive for regardless of the reason, and as interest in catching trophy bass increases so too does the anglers pursuit of knowledge concerning the life history of his quarry.


People ask me all the time how long it takes for a largemouth bass to grow to 10-pounds. I always struggle to answer this question, because the answer isn’t simple or straight forward.

Growth of all fish is a complex process, is highly variable across both space and time, and is a synergism of many factors. Growth rates for any particular lake are in a constant state of change due to the dynamic nature of aquatic ecosystems. In this article I’ll do my best to simplify the complexities of fish growth and give a very general idea on how many years it takes for a largemouth bass to grow to 10-pounds.

Growth can be described in terms of either length or weight, and is a component of a fishs’ energy balance equation where consumption= total metabolism + waste losses + growth.


Simplified, this equation says that the total calories consumed by a fish are partitioned into three major physiological processes.

The percentage of consumed calories dedicated to each process differs between herbivores and carnivores. For the typical carnivore living in a habitat under average environmental conditions, the energy budget can be approximated as 100 percent of consumed calories = 44 percent total metabolism + 27 percent waste losses + 29 percent growth.

As a fish consumes more calories growth increases because more calories can be allocated to growth. Caloric content varies among prey items. Prey items having higher levels of lipids and protein have a higher caloric content per unit size so to speak.

A bass population whose primary prey is high in calories will, all other factors held constant and being average, have above average growth rates. California anglers probably won’t be surprised to learn that trout and kokanee have very high levels of lipids and protein when compared to more traditional prey items.

Keep in mind the above energy budget is highly generalized and each process shows high variation. The variation is primarily introduced from differences in environmental conditions, prey resources, and predator/prey densities and interactions. For example, we all know air temperature, and therefore water temperature, has spatial gradients.

Growth gradients follow temperature gradients so what you see is slower growth at northern latitudes when compared to southern latitudes. Variation in temperature across the landscape influences growth at a broad scale, while other factors show variation at much smaller scales.


What I mean by this is many factors influencing bass growth function at the lake level. Two superficially similar lakes located close to each other can show very different growth rates. Growth may differ due to differences in water quality, the balance between predator and prey populations, harvest regulations, and genetics.

One lake may have superior water quality (no pollution, good dissolved oxygen content, optimal fertility) and the other shows poor water quality, maybe because of raw sewage input or agricultural runoff.

Poor water quality can cause stress which can reduce growth rates. Likewise, one lake may have the perfect number of bass given the amount of available prey while the other lake has too many bass for the amount of prey.

The later case is a bass crowded situation and the resultant stunted population has very poor growth rates. Caloric content of prey items, as mentioned, can strongly influence growth and thus the number of years it takes for a bass to grow to 10-pounds.

Given a choice of fishing adjacent lakes, I personally would always choose the lake having populations of trout and kokanee.


So, how long does it take for a largemouth to grow to 10-pounds? The only way to answer this question with any level of confidence is to have data, and data concerning the age of such a limited resource are limited. There are several reasons for this. Ageing fish using the traditional method of fish scales is only accurate for fish up to about 4 to 5 years of age. With heavier and older fish, to get a truly accurate age, otoliths are used and this requires sacrificing the fish. Managers and fisherman alike are not likely to sacrifice a trophy fish for any reason. Therefore there is a lack of age data for double digit largemouth. However, based on my experience, I can provide some generalities.

I would say it takes on average seven to 11 years for largemouth to grow to 10-pounds in regions and lakes that consistently produce double-digit largemouths. Don’t hold me to these numbers because I have aged fish from different places in California, where the age seriously surprised me! For example, I wouldn’t be surprised if certain lakes in Southern California produce double-digits in four to five years. I never would have thought this possible until I aged a few true giants from that region. On the other side, I have aged fish from Northern California that were much older than I expected.

Courtesy photo Image showing a sectioned and polished otolith from a 7-year-old largemouth bass. N = nucleus which represents when the fish hatched; A = annulus number or growth ring number.


Double-digit largemouths are a limited resource in any region. In many places it takes much longer than 7 to 11 years for a bass to grow to such weights. I can’t stress enough how important it is to take good care of these fish when captured. Always plan ahead by making sure you have a good camera, accurate scale, and a measuring tape.

If you fish alone make sure you have devised and tested a way for you to take good photos of yourself with your catch. Excellent reproduction mounts can be made provided an angler gets an accurate weight, takes good photos, and takes length and girth measurements. Harvesting large fish for mounting is no longer necessary.


Plus, releasing a giant largemouth and watching it swim away healthy is an indescribable feeling that increases the personal satisfaction of catching that fish by tenfold. Try it sometime, I promise it is addicting.

For example, a largemouth from the California Delta that weighed 9.69 pounds was 12-years-old, while a 7.94 pounder from Berryessa was 10-years-old.

Consider this before you take these numbers to heart. These fish were only one fish and do not necessarily represent the population average. Population averages can only be determined, at least statistically, through many samples. Getting enough samples to get a better picture of the age structure of a lakes trophy population is always a major barrier.

Steve Pagliughi was a fisheries and wildlife biologist in Sacramento, CA. He was involved in an independent study of the age and growth characteristics of trophy bass from California waters. Samples for this study are acquired from anglers and managers who have a trophy bass expire on them during either fishing activities or management activities.