Saltwater Fish Compatibility Compatibility problems arise for a number of reasons. Natural aggression, territory disputes, breeding and feeding habits account for most of the compatibility problems in community saltwater tank environments. In the wild, individuals and groups of fish can often find relief from the relentless attacks, but in the restricted tank environment, compatibility issues often result in death for the less aggressive or smaller fish. Signs of incompatibility are obvious - fin nipping, endless chasing, hiding, lacerations, and, of course, dead or missing fish. Many saltwater fish seek hiding places at night and disputes often arise over sleeping places. Whatever the reason or cause of incompatibility, little can be done on the part of the keeper to modify the behavior and is best to remove the aggressor or the victim to another tank. A general rule of thumb in keeping saltwater fish together is the more the fish resemble each other in size, shape and color, the more likely there will be compatibility problems. Most fish books recommend keeping one member of each species together in the aquarium. Schooling fish, such as cardinals and yellow tangs, can be kept in groups if they are introduced to the tank at the same time. Survival dictates that all species aggressively look for and protect food sources and territory, but some species are more naturally aggressive than others. Usually aggression is a predator/prey behavior where the smaller, less aggressive fish is beaten up or eaten. In the tank, this situation is unavoidable and it is best to keep aggressive fish with other fish that can hold their own. Fish, like may other species, are territorial. There are no hard and fast rules about territory in a saltwater tank except one - have as much territory per fish as possible. The smaller the tank the greater the competition for space. Competition for space even in large tanks can be fierce if the tank is overcrowded. When disputes persist or when adding new fish, rearrange corals and other decorations so all tank mates begin establishing territory at the same time. Compatibility problems can develop with fish that have been kept together for a year or longer. Like other animals, as fish mature physically and sexually their behavior changes and they can become aggressive and begin to cause problems. Incompatibility can have larger implications to the overall health of the aquarium. Relentless aggression by a single fish results in a stressful situation to all tank mates, even if they are not the primary recipients of the abuse. Reluctance to feed and hiding are common coping behaviors of tank mates affected by an aggressive environment. If the victim is not killed within a few hours but lingers with open wounds that become infected, pathogens can spread to other fish. Intervention on the part of the keeper can restore order by rescuing a brutalized fish or removing a bullying offender. A net and a cage are essential until a permanent solution can be found. Better aquarium shops are reliable sources of information about fish compatibility and most discourage keepers from mixing species with a history of incompatibility. These stores often have return policies that prevent keepers from returning incompatible fish if they were warned in advance that a particular fish will either cause or suffer problems. Responsible fish keepers follow good advice and take the necessary steps to maintain a peaceful, healthy environment. Saltwater Compatibility Chart Back to Aquarium Home Page