Anton Wernher I have no experience with this lovely darters, but here's some info/sites I happened across a while back...not sure if it will help.....
USGS
Ontario Freshwater Fishes Database
Artical taken from here:
Minnesota Aquarium Society
Etheostoma caeruleum, The Rainbow Darter:
caeruleum = blue or a shade of blue
The rainbow darter is one of the more common species of darters in the small rivers and streams of southeast Minnesota. It adapts well to life in an aquarium despite the fact that its preferred habitat is the swift water of riffles and rapids.
As its common name implies, the rainbow darter is one of the more colorful species of darter inhabiting Minnesota waters. In fact, breeding males may display all the colors of the spectrum. The fish's body is olive colored with blotches of dark olive on the back and upper body. There are about 12 bars of indigo blue that extend downward and backward. The spaces between the bars are brilliant orange and the chest is orangish red. The first dorsal fin has blue and orange horizontal bars. The females are a subdued brownish gray color on their body and fins. Of both fish the body is moderately robust, and compressed laterally. The average length is 64mm (2.5in). The snout is rather pointed and the mouth almost horizontal with the lowerjaw slightly included within the upper jaw. The first or spiny dorsal fin has 8-13 spines and the second dorsal fin has 10-15 rays. The anal fin has two spines and 6-8 rays. The pelvic fin is thoracic and the pectoral fin length is generally slightly shorter than the head length. The lateral line is incomplete with 20-34 pored scales.
The male is larger and his anal fin, first dorsal fin, pectoral fin, and pelvic fins are longer than are the females. The male's urogenital papilla is small and conical. The female's is swollen, broad, and flat topped.
Etheostoma caeruleum typically inhabit creeks and small rivers of moderate gradient and riffles composed of coarse gravel and rubble. They are sometimes the most abundant darter under such conditions and are captured with a greater variety of other darters than any species with the possible exception of Etheostoma flabellare. The rainbow darter ranges from southern Minnesota to eastern Ontario and south to Alabama and Arkansas. In Wisconsin the rainbow darter was found most frequently in clear water at depths of 0.1-0.5 meters over substrates of sand (25%), boulders (25%), gravel (25%), silt (13%), rubble (11%), clay (2%), and mud (2%). It has been collected from swift to moderate currents in streams - from riffles (40%) and from pools (60%). It was present in streams from 3 meters to more than 100 meters in width but reached its greatest numbers in streams 12-24 meters wide.
Breeding reaches its peak as water temperatures reach 17-18°C. Males have shifting, ill defined territories and practice intimidation on intruding males. Females enter the spawning ground from pools downstream and lay eggs in the gravel at the foot of riffles. Several days are required for a female to deposit a maximum 800 eggs. An abrupt drop in water temperature will interrupt spawning, as will increased turbidity, since vision is the most important sense used by rainbow darters in spawning activities. The spawning area consists of fine gravel, large gravel, rubble, or a mixture of gravel and rubble in swift riffles about 0.3m deep with a flow of 23 meters per minute.
The large, brightly colored males defend territories which are generally restricted to specific areas, often where there is a large rock or a depression in the gravel with the largest, most colorfull males establishing the territories in the center of the spawning grounds.
When a female darter enters the spawning ground, a male comes up from behind and follows, swimming parallel to the female and prodding her side with his snout. When the female is ready to spawn she will bury the ventral portion of her body and her pectoral fins then the male will mount her to fertilize the eggs. Three to seven eggs are released with each spawning act. After the female has completed a few spawnings, she will return to the pool to rest.
Mature Etheostoma caeruleum eggs are 1.0-1.8mm in diameter, yellow to orange in color, with a single oil droplet. They are left buried in the gravel and receive no further care from either parent. Neither the spawning pair nor other darters in the area have been observed eating their eggs in their natural setting but they were seen eating the eggs in the laboratory. Hatching occurs in 10-11.5 days at 17-18.5°C (63-65°F).
Robert Thomas of the North American Native Fishes Association has published in the October 1985 issue of American Currents an account of spawning these fish in an aquarium. He kept three pairs of these fish in a 20 gallon low tank. They spawned for him using spawning mops made from dark brown dacron rug yarn sunk down to the bottom of the tank - which had no gravel. He removed the eggs from the mops and placed them in a petri dish. After hatching, he moved the fry to a shoebox. The fry became free swimming in about 4-5 days and were able to eat microworms right away.
When placed in the home aquarium, males are found to loose their bright colors gradually. In experimental tanks with controlled temperature and light cycles, the rainbow darter is more responsive and undergoes considerable seasonal change.
