Why all this sudden aggression?

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One of our readers has noticed that one of his male rams has started chasing the all the other fish in his tank, Max Pedley offers his advice…

Q: I have a pair of Bolivian rams, which I believe to be a male and a female, in a 200 l tank with X-ray tetras and a couple of nerite snails. When I first added the rams about 18 months ago, one bit a chunk out of one of the tetras but since then they have been getting along fine. Recently, the ram that I believe to be male has started chasing all the other fish, including the other ram. Is this a problem or just mating behaviour? They have had a few batches of eggs in the past but never successfully bred. The tank is well planted with real and artificial plants and various hiding places.

RICHARD DODDS, VIA EMAIL

A: Max says: I’ve always had the best success when keeping Bolivian rams in small groups. Like many other members of the Geophagus subfamily, they are quite gregarious fish.

In small numbers, dominant fish often become overwhelming, taking their frustration out on other fish, especially conspecifics.

To reduce aggression, it’s a good idea to increase the group size up to six individuals or so. This helps to spread and therefore dilute the aggression. Of course, established pairs may be fine together, but repeated, failed spawning attempts often lead to a ‘relationship breakdown’, and this can result in aggression, which is what seems to have happened in your case.