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DNA & Lake Ontario Bass Diets

DNA approach provides valuable insights into Lake Ontario bass diets

With shows like CSI on TV, most people are familiar with the potential use of DNA to catch criminals. These days, scientists are also using DNA approaches in many other interesting ways. This post describes how we are now using a DNA approach to improve our understanding of the prey consumed by Smallmouth and Largemouth Bass in Lake Ontario. If you are interested in learning more about this, some additional information is provided below…

Understanding “who eats who” in food webs is a challenging problem, but it is very important information for biologists who are trying to understand how ecosystems function. From an angling perspective, knowing what bass really eat is also extremely valuable information.

Traditional methods for diet analysis that rely on visual identification of stomach contents can be frustrating because many food items are often partially digested. Not surprisingly, many things end up being classified as “unknown” items using this approach. When DNA is extracted from stomach contents, however, the power to identify prey items can be greatly increased.

The first photo in this post shows 17 items found in the stomach of one Smallmouth Bass from Lake Ontario. Only one of these fish could be easily identified as a Round Goby using visual methods. After extracting DNA from these samples, however, and then running a simple test to determine if it came from Round Goby (see second photo), we can conclusively identify all 17 items as Round Gobies.

For Smallmouth Bass, DNA methods have resulted in a list of identified prey items that is now 5 times longer. Not surprisingly, most of the items in Smallmouth stomachs are Round Gobies, but others are Alewife and crawfish. For Largemouth Bass, DNA methods have allowed us to see that the diet is much more variable and includes many species that had previously gone undetected. Anglers who fish for Largemouth will appreciate the fact that the list of diet items looks more like a list of whatever swam too close. These fish are definitely opportunists! In addition to many Round Gobies, Largemouth stomachs contained Crawfish, Bluegill, Pumpkinseed, Golden Shiner, Rock Bass, Alewife, Brown Bullheads and even a small Bowfin!

The stomach contents of Lake Ontario Smallmouth Bass #289. This fish weighed 4 pounds, 7 oz and actually had 17 prey items in its stomach! This was the highest number of prey items found in any of our fish to date. Only one of these fish items could be easily identified as a Round Goby using traditional (visual) methods.

Huck Nelson at work on this project in the Freshwater Fisheries Conservation Lab. Huck has excellent skills in molecular biology and this study is the basis for his 4th year thesis.

This is what the results look like for the experiment run on the DNA from the remaining 16 “unidentified” items shown in the 1st photo. The bright bands in the 1st two rows show that the appropriate “barcode region” of DNA has been isolated for these experiments. The bottom row (Round Goby Test) shows the results of a test that will snip this DNA into 2 pieces if it is from Round Goby. For each of these stomach items, the test resulted in 2 bands – confirming that this Smallmouth had actually eaten 17 Round Gobies!

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