It is the time of year I setup home aquarium to breed Bantam Sunfish. This round the tank is larger around 125 gallons so able to keep a range of sizes in addition to multiple males and females. This go males are all small age-1 as are the females. Males will be the smallest I have attempted to breed but they seem to be getting into the mood without trouble. Largest male pushing 1.25 inches and before in the mood had dorsal spot of juveniles and females. As males start getting into breeding mode they periodically loose the spot but when relaxed the spot is restored. Females can drop spot while actually spawning.
I am wondering what the spot does for the fish. With really small Bantams is may play the same signalling role it has with Bluegill and Green Sunfish. Tanks I have been using may causing a container effecting masking behaviors the spot might be important for.