I'm "mature" and a giller too...but never ran into that. I ran into a strange insect hatch on sept 29 one yr on a local lake that had fish making small circle waves on the surface but never saw them with their fins sticking out of the water. Maybe some strange stratification of the oxygen to the surface or zoo plankton on the surface maybe? On a side note, I talked to a neighbor today that said he already had gills spawning in his pond. We are a good deal south and warmer than you though. I usually think the prime for that is mid may.
HHD
GnawMart Tenderloin Sandwich Prostaff, Gnawbone Indiana