Selective breeding yields faster growing largemouth
For bass anglers, bigger is better. This mantra has stimulated fisheries management agencies to introduce larger-growing, Florida-strain largemouth bass into northern fisheries where water temperatures remain sufficiently warm for their survival. Texas, which has long maintained an aggressive Florida bass-stocking program, went one step further: stocking the progeny of bass bred from the biggest bass caught in Texas.
Selective breeding has been practiced for centuries by agriculturists to produce crops and livestock with better yields or other desirable characteristics. The Texas Parks and Wildlife Department’s ShareLunker program began in 1986 to promote angler involvement in fisheries management and, relying on the fundamentals of selective breeding, produce bigger bass. A study by TPWD biologists provides a first look at whether selective breeding can produce bigger bass.
The ShareLunker program involves mating trophy female largemouth bass donated by anglers with pure, Florida-strain largemouth bass males and raising the progeny for stocking into Texas reservoirs. The cost of producing these selectively bred ShareLunker bass is 20 times greater than the cost of producing Florida-strain bass. After 30 years of pursuing a “good idea” and with advances in genetic analysis that allow definitive identification of a bass’s parentage, it was time to see if the expensive effort was actually working.
Samples of 4-year-old bass were collected from six Texas reservoirs stocked with ShareLunker progeny. All lakes previously had been stocked with Florida-strain bass, so the resident bass naturally spawned in the lake had Florida bass genes and the potential to produce outsized bass. Modern genetic techniques and computer programs that allowed identification of the parental fish from fin clips enabled the ShareLunker bass to be distinguished from the resident bass.
The ShareLunker bass were longer and heavier than the resident bass in five of the six lakes, and the lengths and weights of age-4 ShareLunker bass were significantly greater than resident bass in three lakes.
Among all six lakes, the average length and weight of age-4 ShareLunker bass was 16.6 inches and 2.62 pounds, while age-4 resident bass were 16.0 inches and 2.18 pounds.
Adding Florida-strain bass to a population of northern largemouth is known to produce larger bass, both from the stocked pure Florida-strain bass and their hybrids with the existing northern bass population. The ShareLunker progeny from the largest bass caught in Texas produced faster-growing bass than bass with some Florida-strain genes. Selective breeding appears to work, but 4-year-old 2-pounders are hardly trophy bass.
Growth to double-digit weight, even for fast-growing Florida-strain bass, takes at least 10 years in Texas waters. The validity of extending the TPWD’s results to predict the growth of fish more than twice as old as the age-4 bass studied requires understanding a little about bass growth.
Fish have “determinate” growth — if they survive to old age, they achieve a certain maximum size. This is largely controlled by genetics.
Bass have a consistent growth trajectory. They grow quickly in length at young ages, but the annual growth increment decreases as the fish get larger. As a bass continues to grow, the annual growth increment diminishes to nearly zero, becoming asymptotic to the maximum length — the determinate length — for the population. This asymptotic length is a population characteristic, and individuals will vary, some growing larger before they die of old age, some dying before they reach asymptotic length.
Fast growth = bigger fish?
An often-repeated adage in fisheries is “grow fast, die young.” So, is the greater length and weight of ShareLunker progeny at age-4 a good indicator that these bass will achieve larger size?
While grow-fast-die-young is sometimes true, it is also often incorrectly applied. Faster-growing largemouth in the South die younger — commonly at 10 to 14 years old — than slower-growing largemouth in the North that die at 18 to 20 years old. The bass growing season is shorter in the North, but both northern and southern largemouth grow to similar determinate lengths — they just get to that length sooner in the South. Size, not age, is a more important determinant of how long bass live.
A more definitive test of the ShareLunker progeny producing larger trophy bass requires analysis of trophy-size bass, but this is not easily done.
First, trophy sized bass are rare in the population. Collecting a sufficient number of fish for a meaningful analysis would be extremely difficult, if not impossible.
Second, comparing growth rate requires knowledge of the age of the bass. Old bass can be accurately aged with otoliths, but collecting otoliths requires sacrificing fish. This would be counterproductive to the goals of TPWD’s trophy fish program and would cause a firestorm with anglers.
The aging problem is partly solved: the same genetic analyses that allow determining a ShareLunker progeny’s parentage can be used to assign a spawn date. The problem, however, remains for aging the wild-spawned resident fish.
Other approaches can be used to assess the contribution of Share Lunker fish to the trophy bass population, so further support for selective breeding to grow bigger bass may be forthcoming. At this point, I would conclude that the effort, although expensive, can produce bigger bass.
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