Hoplosternum does not mingle with other members of its species
I have had (probably) 4 Hoplosternum cf. magdalenae for about 6 weeks. At least the pictures of these species come closest to my fish. I purchased them in the specialized trade, their color is black and brown with a black dotted white belly.
One of them, however, looks different: bright brown. It does not mingle with the other members of his kind. The fins appear clamped, belly shape is normal, there are no outer disease symptoms. It swims very slowly and is considerably smaller than the other three ones.
I understand it this way that the fish (except for the clamped fins) looked like this from the beginning and did not change its color in the meantime (fright coloration, skin slime due to an infection etc.). In that case it is very likely that it is not of the same species but from another one (which does not occur too rarely, at least with wild caught fish - think of a 'bycatch'). It is actually possible that the fish is ignored or even suppressed by the other ones, which would explain the behavior. Provided I interpreted the situation correctly, there is only one solution: Get the fish "real" members of its own kind (I know this is difficult with bycatches...), and possibly (depending on available and required space) keep them in another tank.
The catfish takes part when I feed them, and it also takes up food. Your guide booklet about fish diseases did not provide me with a clear hint. What would you recommend?
Besides the above mentioned, it is advisable to examine a skin swab (that is not much effort after all, povided you can catch the fish - just be careful about the hard fin spines!). This will allow you to detect a possible skin infection.
Dr. Bodo Schnell