Article © Julian Dignall, uploaded May 01, 1998.
This mimic is the most frequently imported of "imitator" Pimelodids which are as a group not often seen by hobbyists. This is a great shame as their small size makes them the most suitable of this South American family for the community tank. They are a scaleless species which look very much like those of the melanistus group of Corydoras. There are also similar Brachyrhamdia that look like C. natteri and C. adolfoi. When I kept an individual with a shoal of Corydoras I noticed that the corys often had nibbled fins. I never caught the culprit red-handed (or finned!), but I am sure it was the impostor in their midst. Perhaps this forms at least part of the reason for this fish evolving in such a way?
Another (possibly complimentary) theory is that an utterly peaceful shoal of Corydoras containing a few Brachyrhamdia may well pass within easy reach of the latter's prey; this behaviour would be difficult to observe meaningfully outside of the natural habitat. In terms of "safety in numbers", there may also be benefits for the Pimeloids fry being raised within the a larger group of armoured Corydoras fry. Spawning of this species is unreported, but any attempts should perhaps take rhe previous suggestion into account?
In the group I kept, this fin-nipping behaviour was curtailed by the addition of two more imitators which shoaled with the original and the six Corydoras delphax also present. Perhaps like Tiger Barbs the presence of more conspecifics reduces aggressive behaviour. At that time I was unable to house enough C. delphax to prove if the ratio of Corydoras to Brachyrhamdia is significant.
From the number of questions raised by the above it is clear we have a lot to learn about this fascinating small group of catfish.
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