Royal Gramma Compatibility

Can you keep royal grammas together in the same aquarium?

Q. Thanks for the great publication. I have one question. I was in a local pet store and, lo and behold, there were two royal grammas in the same “cube.” Cube is the best way I can describe this pet store setup. An employee informed me that one of the fish jumped over the divider to be with the other fish! Any thoughts? Any past articles I may have missed? (I have a closet full of AFIs). I have always read and been told that there should only be one royal gramma per tank.

A. It is possible to keep more than one royal gramma (Gramma loreto) in the same tank, although I would provide much more space than is available in a typical holding “cube.” Grammas can be kept in groups in the aquarium, but they should not be overcrowded and should be of varying sizes. Although several juveniles can be kept in aquariums as small as a standard 30-gallon tank, an aggregation containing adult specimens should be housed in nothing less than a 55-gallon tank.

Field studies show that royal grammas defend a territory varying from approximately 20 to 560 square inches in area. A standard 55-gallon tank has a surface area of about 670 square inches. Ideally, a group should be composed of one medium-size or large individual and two or more smaller specimens (the latter number depends on how large the aquarium is). If you are keeping more than one large specimen (male) in an aquarium, I believe the tank should have a surface area of more than 1000 square inches.

The only difference between the sexes is size — on average, males are larger overall than females and attain a greater length. Therefore, by placing one larger fish and several small fish in an aquarium, you’re increasing the chances that you will acquire only one male and several females. If you have a smaller aquarium (less than 30 gallons) you should keep only one gramma, or possibly a male-female pair.

Royal grammas will viciously defend a preferred hiding place from intrusion. They will threaten members of their own species, as well as other fish, by swimming toward them with their mouths open wide. If aggression escalates between two grammas, they may lock jaws and headshake, or nip at each other’s fins and bodies. If this kind of interaction becomes frequent or reaches this level, it is best to separate them before permanent damage occurs. I have seen individuals severely injure the skeletal elements of the jaws during these ritualized battles.

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