It's easier and cheaper to get an annual MI fishing license and collect your own fish. Sunfish and other game fish can be kept in tanks if caught legally and are legal size, and non-game fish such as darters, minnows, and "forage fish" can be kept as well.
Max size seine net in MI is 12' x 4' I believe; I use 8' x 4' as it's easy to use.
All sunfish can be easily caught on hook/line. File off or pinch down the barb of the hook to lessen the injury to the fish.
Peak time for Darter coloration is late Feb. into March when they are spawning in shallow rocky riffles of clean local streams. Wear waders and dress warm.