I've got a 31,7 gallon tank in which about 35 fishes live. For cleaner fishes it is: 2 Antenna catfish (black and brown) and since almost 4 weeks now also 5 armored catfish (others are all non cleaner fish).

While 1 antenna catfish was lazy to start with the other (black) was always very very (hyper)active. Moving along the glass window constantly and cleaning / eating. Also he was within minutes on a fodder tablet when it was thrown in.

A good week ago his behaviour changed almost over night. He is almost constantly only at 1 location and ignores the fodder tablets completely. He still changes places on the glass, but not constantly like before but more like 1-3 times per day in total.

Other things I noticed

  • The fish is under 1 year in age. He is in the tank since 2-3 months.
  • If a fish gets too near and tries to bite him...he reacts as aggresively as in the past
  • When he moves a bit along the glass I do not notice any lack of strength with him holding onto the glass (thus as strong as always)
  • There is nothing on his body that seems like it changed (no inflated stomach or visible fungus, ...)
  • There was a problem with the filter 4 weeks ago which quite a few fishes their lives (I overlooked that I had to remove the filter compltely to see if it is too dirty to work any longer....lesson learnt even if it was a very sad one back then). Aside from that and one homicidal fish in the tank there is nothing that seems to have changed or is out of order.
  • Fishes are fed with the tablets and flake lining (same as since months).

As I know from past experiences a sudden behvaioural change is almost never a good sign I'm quite a bit distressed there, but at a loos as to what to do (or if I'm overreacting and that change is normal).

So the question is: Is there anything I can do there or look out for?

  • As a small update that one fish died today. But dtill interested in what i could have done additionally
    – Thomas
    Mar 1, 2019 at 15:21
  • Someone mentioned to me that its not antenna catfish (a straight translation into english) but instead Suckermouth Catfish. I corrected the title appropriately, but could someone clarify if that is correct so? tnx
    – Thomas
    Mar 1, 2019 at 22:46
  • hei @Thomas your tanks is small for a Hypostomus plecostomus, check your water parameters and say it, is important to know how is your water for determiante what happend here.
    – Gawey
    Mar 25, 2019 at 14:41
  • @Gawey not sure I correctly calculated it (size). it is a 120L tank. From what I heard that fish needs at least a 100L tank? or am I wrong?
    – Thomas
    Mar 25, 2019 at 15:03
  • u are wrong, just search "plecostomus" size and u will see that is a 60cm of fish. So is a best option for this tank one ancistrus than him.
    – Gawey
    Mar 26, 2019 at 7:22


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