A hybrid is a cross between two different species. A significant amount of the research has been done on the female red ear sunfish being crossed with the male bluegill. The red ear sunfish is native to the southern U.S. but not the northern states. Consequently, the hybrid cross that could be raised in the northern states uses a female green sunfish and a male bluegill. There is less research on this cross, but Dr. Joe Morris from Iowa University has done some work on this hybrid. The following is a quote from his work.
“The sex of a selected parent species affects the F1 (first generation) offspring performance and sex ratios. For example, the most common hybrid parents are the green sunfish female and bluegill male; this cross produces F1 offspring with many desirable characteristics (skewed sex ratio, rapid growth rate); however, the reverse cross does not.”
Determining the sex of each specie being used is critical to achieve the results Dr. Morris is referring to. Both the male and female green sunfish are a drab green, and are not easy to tell apart unless it is spawning time. Just before spawning the female’s enlarged gut can carry 2,000 to 26,000 eggs. Many fish producers skip this sex differentiation step and just put green sunfish and bluegills in a pond together and let them spawn. So the prospective buyer may be getting a mix of all kinds of young, including green sunfish instead of hybrids. The only certainty is that the young coming from this first generation you purchase, will have young that are green sunfish, not bluegill.
Predator fish normally eat green sunfish only after they have consumed most of their other food sources. Green sunfish are not the PREFFERED food for any fish. Knowing that small females can carry 2,000 to 3,000 eggs, you can see how after just a couple of years your pond can be overrun with small green sun fish. A true hybrid will grow more rapidly than a regular bluegill. They demonstrate what is termed hybrid vigor, in other words aggressive feeding behavior. They out compete their fellow pond inhabitants for the available food. So the growth of other fish is diminished by the hybrids aggressive behavior. This diminished growth of your other fish is also a negative for your eco-system. There is still much more that could be said about their effect on the all-important zooplankton populations in the pond and therefore the overall food chain. If you are interested in a further discussion of this topic call Jim in the evening (just not on Tues.) at 920-982-6623.