Using high-tech science to test old-school management.
Farm ponds provide abundant recreational fishing opportunities, and a simple fish community of largemouth bass and bluegill — or bluegill and redear sunfish — is a proven recipe for producing satisfying fishing in thousands of ponds.
Both bass and sunfish are desirable sportfish, the sunfish provide necessary forage for piscivorous bass, and bass control the numbers of the prolific sunfish. Many pond owners provide pelleted feed to improve the growth and reproduction of sunfish that may, in turn, improve the better growth rates of bass. Stocking threadfin shad is also recommended by pond managers if trophy bass is a management goal.
Benefits of supplemental feeding can be evaluated by measuring sunfish and bass growth, but many factors can affect growth. Diet studies are needed to assess the effects of supplemental feeding.
Diets of fish historically have been assessed by examining stomach contents. What is in the stomach is clear evidence of what the fish ate in the few hours before sampling but does not, without repeated sampling, describe the diet over longer time frames like a season or a year. Stable food isotopes are incorporated in fish tissue. Thus, stable isotope ratios, particularly carbon and nitrogen, in fish tissues provides insights about food resources consumed.
A study by Auburn University fisheries researchers evaluated the effects of supplemental feeding with pelleted feed and threadfin shad by measuring changes in bass and bluegill growth rate and also measuring stable isotope ratios to track the flow of energy through the simple ecosystems.
Ten 1/4-acre ponds were drained and dried to ensure no unwanted fish were present, then filled and stocked with young bluegill and largemouth bass in the spring. Two ponds received one of five feeding rates ranging from zero to 4 pounds of pelleted food per acre daily. Fish were harvested at end of summer.
Bluegill body weights and ovary weights were positively related to feeding rates. Nitrogen isotope ratios suggested bluegill were feeding on the pellets. Bass body weight and stable isotope ratios were not related to the feeding rate.
Thirty fertilized bass-bluegill ponds, 2 to 58 acres, were assessed. Ten ponds were not fed (control ponds), 10 ponds received pelleted feed (fed ponds), and 10 ponds received pelleted feed and were stocked with threadfin shad (fed-shad ponds).
Growth rates for bluegill, indexed by length at age 2, and relative weight, a measure of body condition or plumpness, did not differ among feeding treatments. Bluegill nitrogen isotope ratios did not differ among feeding treatments and were not related to growth rate. Bluegill carbon isotope ratios were similar to the carbon isotope ratios of the pelleted feed.
Largemouth bass growth rate, indexed by length at age 2, was greater in the fed-shad ponds than in the control ponds but not different from the fed ponds. Nitrogen isotope ratios did not differ among feeding treatments and were not related to growth rate. Carbon isotope ratios in the fed and fed-shad ponds differed from the control ponds but were not related to growth rate. Carbon isotope ratios were similar to pelleted feed but different from threadfin shad.
What does it mean?
The correlation of bluegill body weight with feeding rate in the research ponds suggests feeding increases bluegill growth, and the nitrogen isotopes confirm that the energy for growth was coming from the pelleted feed. But similar results were not obtained in the fed, established ponds. This was likely a result of low feeding rates. Average feeding rate in the established ponds was only 0.9 pounds per acre per day. If you are investing time and money feeding bluegills, feed enough to make it work.
How much feed is enough? Consistently high growth in the research ponds was achieved at 4 pounds of feed per acre per day. Although the growth of bluegills in the research ponds was positively related to feeding rate, wide variation in growth at lower feeding rates in this study precludes estimating a minimum feeding rate that benefits bluegill growth lower than 4 pounds per acre per day.
Dr. Wes Neal, fisheries extension specialist at Mississippi State University, offers some simple guidance for feeding bluegills: use a floating feed, and feed as much as sunfish can eat in 5 to 10 minutes. A floating feeding ring keeps the feed where the fish can get it and where you can monitor consumption. And now is the time to start feeding.
Bass growth in the established ponds was related to the presence of threadfin shad. Bass growth was not related to feeding pellets in either the research or established ponds, yet carbon isotope measurement indicated that bluegills that fed on pelleted feed were, in turn, eaten by the bass. The study authors interpreted these results as bluegill are the predominant forage of bass in these ponds, but threadfin shad provide additional energy to boost bass growth. If this is the case, pond owners interested in good bass fishing should maintain a robust bluegill forage base and view threadfin shad as a supplement to that forage base.