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May 11, 2009
Size Large Genes
Florida Largemouth Bass Changed Texas Fishing Forever
ATHENS, Texas — If shooting fish in a barrel is easy, showing why Texas bass are bigger than ever is even easier.
While not even the editors of the American Heritage Dictionary of Idioms can come up with an explanation of where or how the expression "shooting fish in a barrel" originated, even this humble writer can ascertain why bigger bass are found in Texas today than 40 years ago.
Three words: Florida. Largemouth. Bass.
But you don’t have to take my word for it. Texas Parks and Wildlife Department (TPWD) inland fisheries geneticist Dijar Lutz-Carrillo has been using the latest technology to analyze DNA from 147 bass weighing 13 pounds or more that have been entered into TPWD’s ShareLunker program since 1995. (Samples were not available from all the entries during that period.)
First, a little background. The largemouth bass native to Texas are commonly called northern largemouth bass (Micropterus salmoides salmoides), and the Texas record for this subspecies was caught in 1945. It weighed 13.5 pounds.
Florida largemouth bass (Micropterus salmoides floridanus) were introduced into Texas public waters in the early 1970s by TPWD. This species is known to attain weights greater than 20 pounds.
Soon the Texas record began to go up, and up and up. The current Texas state largemouth bass record stands at 18.18 pounds and came from Lake Fork in 1992.
In what might qualify as a classic case of "Duh," Lutz-Carrillo found that of the 147 fish mentioned above, 76, or 52 percent, were pure Florida largemouth bass. Another 58, or 39 percent, were crosses between Florida and northern bass in which the Florida influence was stronger. That’s a total of 91 percent in which the Florida bass genes dominated.
That comes as no surprise, but it’s scientific confirmation of what TPWD inland fisheries biologists have been saying for years: TPWD’s fish stocking program works.
But there were some surprises in the data, too.
Fish from Lake Fork, which has been stocked only with Florida bass (no northern bass) since its construction, produced 47 of the fish Lutz-Carrillo analyzed. Yet only 30 percent of those fish were pure Florida. Another 53 percent had more Florida than northern genes. And four of the fish actually had more northern than Florida genes. Where did the northern bass genes come from? Most likely there were northern bass present in streams feeding the lake, and nature took its course.
Lake Alan Henry, near Lubbock, has also been stocked exclusively with Florida largemouth. Yet not all the 23 big fish analyzed had only Florida bass genes. Either northern largemouth somehow found their way into the lake, or some stocked fish had both northern and Florida genes. Genetic testing of just a few years ago was not as precise as it is today.
Falcon International Reservoir had four fish in the study. None of the fish in the study were pure Florida, but Florida genes dominated in all of them.
One thing does come through loud and clear from the figures: Not one single fish of the 147 was a pure northern largemouth, the native species. The impact of stocking Florida bass on the genetic make-up of the population couldn’t be more evident. Florida genes make bigger bass, even in Texas.
Yet even bigger bass may be in Texas anglers’ future. TPWD’s ShareLunker program uses 13-pound or bigger bass donated by anglers in a selective breeding program, stocking the resulting fingerlings into public waters. Most are stocked as 1.5-inch fingerlings (some 78,000 in 2008), but a portion are designated as Operation World Record (OWR) fish and are reared to six inches before being stocked (more than 59,000 in 2008).
The growth of the OWR fish is being monitored and compared to growth rates of wild fish by TPWD biologists. Now in its fourth year, the program collected fish from Lake Raven, a small lake in Huntsville State Park, that give a hint of what may lie ahead.
While the average four-year-old wild fish from Lake Raven weighed 2.23 pounds, the average OWR fish weighed 2.88 pounds. And one of those OWR fish was 23 inches long and weighed a whopping 7.23 pounds!
Allen Forshage, now director of the Texas Freshwater Fisheries Center in Athens, where the ShareLunker and OWR programs are headquartered, was one of the biologists who worked with the Florida bass introductions. "The introduction of Florida largemouth bass and the implementation of regulations that protect larger fish have had a profound impact on Texas bass fishing," said Forshage. "The ShareLunker program has documented the catch of large fish and has provided the resources such as funding for the DNA research and the brood fish to make fishing even better."
Fingerprinting Fish: Who’s Your Daddy?
Using the same DNA fingerprinting techniques portrayed in television shows about forensics laboratories, TPWD geneticist Dijar Lutz-Carrillo can identify stocked progeny of ShareLunkers. He can tell which fish were their parents, too.
While it sounds like magic, what’s really involved is many hours of tedious laboratory work. "Since January 2004 tissue samples have been collected from every fish entered into the ShareLunker program," Lutz-Carrillo explained. "Prior to that archival of the tissue was sporadic. The samples, preserved in cryovials filled with ethanol, have been archived in a superfreezer at -80°C.
"Over the years the methods for evaluating the taxonomic status of lunkers has changed considerably," Lutz-Carrillo continued. "The ShareLunker program was established in 1986, and until October 2005 all the entries were evaluated using one to three diagnostic genetic markers or not at all."
But bass fishing was changing in Texas, and so was the science used to analyze the tissue samples from big fish. "Methods based on nucleic acids rather than amino acids were on the horizon," Lutz-Carrillo said. "These new methods allow less invasive sampling techniques, easier preservation methods and the analysis of a greater number of markers, which gives more accurate results."
Using equipment funded by the ShareLunker program sponsor, Lutz-Carrillo refined the DNA testing on largemouth bass. "In 2005 we optimized reactions to amplify six microsatellite loci in largemouth bass," he said. "Two of these were diagnostic for taxonomy. Soon after, the National Institute of Health’s National Center for Biotechnology posted 1,391 bases from the largemouth bass genome on GenBank. In the middle of this sequence the motif CA (for the bases cytosine and adenine) was repeated 18 times in a tandem array-a classic microsatellite. We quickly designed primers and optimized methods for amplifying this repetitive sequence in our lab."
Lutz-Carrillo found that the northern and Florida largemouth bass have different numbers of repeats in the sequence, which gave him a third diagnostic microsatellite.
"At the same time we were partnering with another lab to identify new microsatellites in the largemouth bass genome," Lutz-Carrillo said. "By 2008 our results were published and available on national and international sequence databases. We identified 52 novel microsatellites, several of which could be used to resolve taxonomy."
Lutz-Carrillo now uses six diagnostic markers to classify every entry into the ShareLunker program and eight polymorphic (highly variable) markers to resolve parentage. Some ShareLunkers are pure Florida and some are hybrids between Florida and northern largemouth. Some hybrids’ genes are dominated by Florida largemouth influence and some by northern.
Significantly, not one single ShareLunker analyzed to date has been a pure northern largemouth. Lutz-Carrillo’s work confirms that the introduction of Florida largemouth bass did indeed change the world of Texas bass fishing.
A Lake Is a Lake Is a Lake...Right?
Given the impact that stocking Florida bass into Texas waters has had on the size and number of big bass caught, it would seem that all you have to do to produce swarms of big bass in any lake is put some Florida bass in and wait a few years.
It’s not quite that simple.
According to an analysis of stocking history and bass size from 89 Texas reservoirs conducted by TPWD Inland Fisheries biologist John Tibbs of Waco, not all lakes are equal when it comes to taking advantage of Florida bass genetics. "In general, nutrient-poor reservoirs in South Texas had significantly higher rates of Florida gene influence than nutrient-rich North Texas reservoirs," Tibbs said. "The size of bass that anglers caught seemed to be influenced more by local reservoir conditions than by Florida genetic influence. Anglers generally caught larger fish in large, shallow, young reservoirs with a high incidence of Florida genetic influence. Largemouth bass growth rates increased from west to east and as elevation decreased."
While Tibbs cautions that his study is not definitive, it seems clear that the most successful stocking policy will result from putting Florida bass into reservoirs that offer the best conditions for bass to express their genetic potential. The downside is that not every lake will probably be a trophy bass lake. The upside is that TPWD can make the most of anglers’ dollars by putting them to work where they will do the most good.
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