Cichlids often gauge the safety of their environment by watching other fish.
Paul V. Loiselle
Q. I bought two jewel fish from my local pet store and put them in my 75-gallon community aquarium with an assortment of barb fish, danios and tetras. While they were in this aquarium, the jewels were always out and visible until someone approached the aquarium. Their behavior was very outgoing, but as they grew larger, some of the smaller fish began disappearing. So I decided to move the jewels into a 29-gallon aquarium well furnished with clay flowerpots, rocks and driftwood. The water temperature in the aquarium is 73 to 75 degrees Fahrenheit, and filtration is provided by an outside power filter containing carbon.
Since they were put in this aquarium the jewels only come out if the room is dimly lit and empty of people. This is the only time I can give them fish food with any expectation that they will eat. Even then, they will only eat canned dog food and earthworms in small amounts.
Why this change in behavior now that they are alone? Is there anything I can do to coax them out of their hiding places? It isn't much fun having fish I never see! Also, what can you tell me about the spawning behavior and needs of jewel fish?
A. Jewel fish, like many cichlids, appear to monitor the behavior of the schooling fish that share their habitat in nature as a means of assessing their own vulnerability to predation. If the fish that share their habitat are swimming freely about, the cichlids can feel secure that no predators are about. If and when these schooling fish abruptly disappear, cichlid fish take cover. Those that fail to take such hints rarely live long enough to breed, so this behavior remains strong over generations.
Students of animal behavior and aquarists alike have long used such "dither" fish to overcome the shyness of cichlids in an aquarium setting and elicit the the full range of their fascinating behaviors. You were inadvertently using the dither principle to overcome the shyness of your new arrivals when you placed them in your community aquarium. The problem, as you have discovered, is choosing companions whose size and behavior allows them to function effectively in this role with minimum risk of making a one-way career shift from dither fish to live food!
Jewel fish are efficient predators, but their relatively small mouths and modest adult size limit their selection of potential prey. Typically, sexually inactive individuals of these Hemichromis species will ignore schooling companions two-thirds their own length or larger. This affords you a pretty wide selection of possible dither fish for your 29-gallon aquarium. If you strive for biogeographic accuracy in your freshwater aquarium fish, both Brycinus longipinnis, the African longfin tetra, or Phenacogrammus interruptus, the Congo tetra, grow too large to make a convenient mouthful for any of the so-called "red jewel fishes."
If you do not mind housing fishes from different parts of the world together, you have many more options to choose from. From South America, Buenos Aires tetras (Hemigrammus caudovittatus) are large and fast enough to stay out of harm's way, as are the silver dollars of the genera Myleus and Metynnis. From Southeast Asia, suitable dither species include Danio aequipinnatus, the giant danio, and mid-size barb species, like Barbus filamentosus, B. everetti and B. lateristriga. Finally, good-sized specimens of such Australasian rainbowfishes as Melanotaenia trifasciata, M. splendida and Glossolepis incissus can also coexist successfully with Hemichromis species.
Hemichromis are substrate-spawning cichlid fish that typically deposit a compact circular plaque of yellowish-white to olive-green eggs on a flat surface previously scrubbed clean by the pair. Male and female share custodial and hygienic duties, although the male usually devotes more time to defending the integrity of the pair's breeding territory. Both parents are ferociously protective of their mobile fry and will attack and even kill fish too large to eat if their aquarium is too small to allow such perceived threats to move beyond the pair's territory. Thus, in a 29-gallon aquarium, the presence of dither fish after the cichlid fish have spawned would be problematic — I would anticipate no problems in your 75-gallon aquarium.
Hemichromis are not, in my experience, picky eaters. I suspect the behavior you describe is due to the combination of low water temperature and the fact that your isolated pair does not feel comfortable in the 29-gallon aquarium. You can solve this by introducing suitable dither fish and raising the water temperature about 5 degrees.