My first stint at keeping South American killifish was in the mid-seventies. At that time, the killies classified as Rivulus were affectionately known as brown worms by most hobbyists. When I returned to the hobby some twenty years later, the ugly duckling Rivulus had been transformed into a very diverse and colorful genus of killifish. With some 92 known species more are being discovered every year. Today there are more species of Rivulus than Aphyosemion.

Most species of Rivulus, as their name implies, inhabit rivulets and other shallow marginal habitats such as springs, swamps, roadside ditches, and have even been found occupying water-filled hoof prints left by cows that had come to the river to drink. A few species prefer brackish water and some can even tolerate full-strength seawater.

THE FISH OUT OF WATER
Rivs are seldom seen in nature unless one is looking among dense vegetation. Wet leaves are a common habitat. They feed strictly on live food (face it, they have teeth) and eat larvae and insects that fall into water. As hunters, they dart and sit awhile watching for prey, then move to a new spot and again sit very still. Rivulus will actually come out of the water onto the bank to get ants and other ground insects. That is why you will often find your Rivulus out of the water, laying on top of the plants or the cork of the mop. Although they are very sedentary by nature, they are capable of moving considerable ...

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