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Sedentary cory

Gypsum

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One of my black corys has become rather lethargic relative to its four pals. It spends a lot of time sitting in one place on the substrate while the others zip about. However, it joins the feeding frenzy when I feed everyone and doesn't look distressed. Not breathing heavily and no unusual marks on it. Water parameters are all copacetic, and I did a big water change yesterday.

Should I be concerned or is this normal behaviour for this species? I've had false julii corys for a while now but these are relatively recent additions. Do I need to increase the black cory school or treat this guy with something or not worry about it?

Tank is 240L.
 
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Gypsum

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I've been watching the cory most of the day. It goes through short periods of activity -- swimming to the surface or 'corying' in the substrate, then periods of inactivity, which are significantly longer than the inactive phases I've observed in the other black corys and the false juliis.
 

Byron

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I would not worry about this. You are correct to observe the respiration, that is a major clue when it comes to fish and cories always respirate faster under any form of stress. Respiration will increase during feeding which obviously is normal, or during activity including pre-spawning. But more rapid respiration when resting for some time may be an indicator of trouble.

Adding any treatment/medication is generally inadvisable unless you are certain there is a specific problem and know which problem it is. All additives will stress the fish more, regardless, and this will only make things worse. Treating a definite issue may be needed, but only when certain. Water changes usually achieve far more. Not that I'm suggesting anything here, just stating the case. Regular weekly partial water changes of no less than 50% and preferably 60-70% of the tank volume (at one time) is beneficial to all fish, provided the parameters (GH, pH and temperature) of tank water and tap water is reasonably the same.

I have had some 50 cories of several species for over ten years now; some species are more active, others considerably less so (a couple I only see during feeding time!). Individuals within a species may be more or less active.
 
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Gypsum

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I did a 50% water change yesterday when I noticed the cory being less active. It hasn't made much difference. We've only had the black corys for a little over a week and they were all pretty manic that first week.
 

Byron

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I did a 50% water change yesterday when I noticed the cory being less active. It hasn't made much difference. We've only had the black corys for a little over a week and they were all pretty manic that first week.
Corydoras fish do not like being moved at all. So when they are acquired and placed in a new environment, they will be very stressed. This can play out in different ways. Sometimes with completely hiding and no swimming about, sometimes with heightened activity. It can take hours to days to even weeks before they may settle. Individual fish may be different from one another in this process. So again, I would not worry.

My point about water changes was a general one; a substantial water change once each week will really go a long way to healthier cories, and all fish for that matter. But don't expect miracles; the fish are stressed and need quiet to settle down in their new home.
 
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Gypsum

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My sedentary cory is looking worse. Today, it hasn't moved since this morning, its fins are clamped, and when I threw some sinking pellets at it, it didn't respond at all (but everything else in the tank did). Still no marks or spots on it, but it's definitely not right.

Any ideas on what my next step should be? Removing it from the tank to treat it with something?
 

Byron

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My sedentary cory is looking worse. Today, it hasn't moved since this morning, its fins are clamped, and when I threw some sinking pellets at it, it didn't respond at all (but everything else in the tank did). Still no marks or spots on it, but it's definitely not right.

Any ideas on what my next step should be? Removing it from the tank to treat it with something?
Leave it alone. As i have already explained, without knowing exactly what the issue is any "treatment" other than clean water and quiet will only make things worse. The cory may recover or it may die; it may be something genetic, it may have been injured in netting (this is common), it may have something.
 
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