Bill, the question was asked, but never answered. CNBG need even warmer water than straight, northern bluegill. Even the intergrade crosses of BG and CNBG often found in Arkansas fish farms frequently die if the ponds just get ice glazed in the winter. Since southern fish farms also stop feeding CNBG in the milder winters, I am sure the CNBG metabolism slows at a higher temperature than BG, since CNBG are less cold tolerant.
Not only are the ponds in different climate regions very different, the species used often are as well.
