Tropical Fish Hobbyist

One of the 50 display tanks featured at the “Cichlid Days” display at the 2007 Duisburg Ornamental Fish and Aquarium Show put on by the German Cichlid Association (DCG) was an unusual yet stunning aquarium of tilapia cichlids put together by Marco Hasselmann of the Berlin Zoo. The tilapia that first drew me to the tank were the three fish with black markings around the mouth and throat—Sarotherodon melanotheron melanotheron—which I had never seen before. There were also five bigger Sarotherodon galilaeus galilaeus, another species that I had not seen. A trio of large yellowish-colored Tilapia mariae and a pair of Chromidotilapia guentheri guentheri completed the tilapia lineup, but there was also a trio of beautiful Hemichromis elongatus and a group of colorful but smaller Hemichromis guttatus.

The Display

These cichlids were housed in a conventionally large aquarium, but due to the size of these fish, there was barely enough room for all of them for the four-day display. There certainly would have been trouble had a pair of any of them decided to spawn. The substrate for the aquarium bottom was fine white sand, which was littered with two dozen or so smooth gray boulders, some arranged in piles to give some of the smaller fish a base to anchor around. The water in this

display was moderately hard and alkaline (DH around 10, pH around 7. 5) with the temperature maintained near 25°C ( 77°F) by two large heaters. Water quality was maintained by two large external canisters that contained a sponge filter to remove particulate debris. These canisters also had several compartments for other types of media, one of which offered a large surface area for colonies of nitrifying bacteria that efficiently converted ammonia and nitrites to nitrates; these nitrates would be reduced by water changes.

I was mesmerized by the large cichlids in this tank and spent a lot of time watching their behavior and photographing them, although they took little notice of my activity. For the most part, the larger cichlids cruised around in pairs or groups, ever so dignified and peaceful, only occasionally stopping to explore the crevices among the rocks. The C. g. guentheri pair, however, was a little reticent and stayed in one corner of the tank for the most part of the first day. The small H. guttatus, on the other hand, were the most aggressive; having claimed a central pile of rocks for their home, they were trying to drive huge fish away, to little avail.