I wonder if the CC are disrupting the nesting of the other fish by rooting around in the nest where the fish lay eggs? If the RES are not big enough to run them off, that may be the reason for low recruitment. CC eating the eggs in the nests.
Size of RES are not an issue as we have caught some close to 2#. I do think the CC group up and raid the nest during spawning. I also wondered if the CC eat a lot of the feed that RES would normally eat. Anyway I never seem to have had much recruitment of RES when combined with higher stocking volume of CC.
