You have mentioned that rainbowfish are known aquatic plant eaters. This is a great shame. I had visions of keeping large schools of rainbowfish, but considering the damage just five have done (they tear shreds off crypts, as well as stem plants), I don’t think an aquarium with them would look too good after a while. I wondered if you had any ideas on how to minimize the plant-eating behavior of these fishes. I thought about feeding a greener diet, and I also wondered about school size and how this might affect behavior.
For many months there were just three dwarf neon rainbowfish in the aquarium, and it was only a while after I added three more that I noticed damage. Any ideas (except muzzling them) would be appreciated. Also, are Nannacara likely to damage aquatic plants? Are dwarf cichlid fish in general renowned aquatic plant nibblers?
While there are certainly fish that will mow a planted aquarium right to the ground (silver dollars come to mind), there are many fish that will eat at least some greenery, but can be managed in a planted aquarium. Many aquatic gardeners, including myself, successfully keep rainbowfish in heavily planted aquariums. If your plants are growing well and your fish are well fed, the damage caused by rainbowfish and many other fish should be minimal.
There are several tricks to keeping fish in a planted aquarium. Make sure your aquarium is really heavily planted, and that your planting includes lots of fast-growing stem plants. Then provide conditions that ensure your aquatic plants grow rapidly and well (good light, correct substrate, trace element supplements and adequate carbon dioxide).
The use of fast-growing aquatic plants, like Hygrophila polysperma and water sprite (Ceratopteris thalictroides), has two advantages. First, these tender plants are usually most attractive to plant-eating fish, so they tend to leave more decorative slow-growing species alone. Second, the plants grow so quickly that they can usually more than keep up with the depredation of the rainbowfish. And yes, feeding green fish food, such as Spirulina flakes or blanched zucchini, can help take the pressure off in a situation where the fish are really damaging the aquatic plants.
Because the term “dwarf cichlid” only denotes that the fish is a cichlid fish of small stature, it would be a mistake to generalize too much about the habits of these fish. Still, there are many dwarf cichlid fish that are excellent candidates for the planted aquarium. Some, such as Nannacara anomala, are actually much more likely to exhibit natural behaviors when kept in the comforting surroundings of a densely planted aquarium, and will not damage the plants.