Some aggressive fish should be paired with other aggressors. Take for instance rainbow sharks, tough guys who will bully smaller and more docile fish, and cichlids, some species of which are extremely aggressive. It's a suitable if not tense arrangement: The right cichlids will stand up for themselves but won't predate your plucky shark.
Choose the Right Tank Mates
Choose cichlids that are the same size as or slightly larger than your shark. Rainbow sharks antagonize fish smaller than themselves; African jewel cichlids and South American ram cichlids are docile and may be targets for harassment from your shark. Avoid very large, very aggressive cichlids like the red devil (Amphilophus labiatus) or the green terror (Andinoacara rivulatus), both of which can reach 12 inches long.
Choose cichlids that are aggressive but not too aggressive. Rainbow sharks will pick on larger fish that are docile. By filling your tank with aggressive or semi-aggressive cichlids they will stand up for themselves against the shark. Avoid nonaggressive cichlids, like the jewel cichlids, that your shark will most likely harass.
Populate the tank with a school of cichlids and only one rainbow shark. Rainbow sharks won't tolerate living with members of their own species. Cichlids are also territorial, but you can control this behavior by overcrowding them in the tank so they have no space to fight over. Include about one cichlid per 8 to 10 gallons of water in your tank.
Mix cichlids of different species if necessary. Some cichlid species get along with their own kind while others fight relentlessly with fish that resemble themselves. The demasoni (Pseudotropheus demasoni), for instance, will attack fish of his own species. You can keep the firemouth, one of the most popular cichlid varieties, in a school or a pair.
Provide the Proper Environment for All Species
Choose the right size of tank for your rainbow shark and the number of cichlids you want to keep with him. Cichlids don't need a lot of tank space, but rainbow sharks need at least a 30-gallon tank, and 55 or more gallons is preferred to house these fish comfortably.
Keep the water quality suitable for all your fish. Rainbow sharks aren't picky about their pH level, but the 6.5 to 7.5 range is ideal. Cichlids like a higher pH, around 7.5. Rainbow sharks like their water between 72 and 82 degrees F. Cichlids like it a bit warmer, between 75 and 85 Fahrenheit, so a 75-to-80-degree range is ideal. Both cichlids and rainbow sharks like hard water, so in this aspect they are good tank mates.
Decorate the tank in a way that suits both the cichlids and your shark. Rainbow sharks do well when they have plenty of free-swimming space at the top of the aquarium to do their laps. Adding decorations and plants at the bottom of the tank provides hiding places for fish who need an escape from each other.
- If your fish are fighting, separate them immediately and rethink your strategy for keeping aggressive fish together. In the worst cases, one of the fighting fish will need to be rehomed.
Madeline Masters works as a dog walker and professional writer. In the past she has worked as a fitness columnist, fundraising copywriter and news reporter. Masters won two Pennsylvania Newspaper Association Awards in 2009. She graduated from Elizabethtown College with a Bachelor of Arts in English.