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Cory consistently on surface

Gypsum

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One of my c. trilineatus has been hovering on the surface of the water with its nose poking out, blowing bubbles, whenever the tank lights go off. It doesn't go up and down very much -- it just stays there. I have seventeen corys of various species in this tank, and this is the only one which shows this behaviour to a strange degree (the others might occasionally dart to the surface, but then go straight back down -- normal behaviour). It's a planted tank, and I'm aware oxygenation levels change at night due to plant 'behaviour,' but I have two airstones, a Fluval 307, and a Fluval U4, all turned up to 11 for maximum water movement. Tank is 240L (55g), and water parameters are all copacetic -- zero ammonia, nitrite, nitrate, soft water because Scotland, etc.

Any explanations? Is there anyone bored on lockdown who has a theory?
 

JuiceBox52

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Theory: the cory wants to be a bird and is learning to breath air to he can learn to fly

I am not sure why this might be... other members may be able to help
 

Byron

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It is likely a problem, but which could be difficult to determine. Water conditions (ammonia, etc) seem OK (assume temperature is normal?) so that is one possible issue eliminated. As the other cories and fish are apparently OK, that eliminates a likely water issue like a toxin. That leaves us with a genetic issue, or an injury, or aggression from another fish (certainly not a cory, they don't do this).
 

Colin_T

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It could be looking for food or having trouble breathing.

Is the fish the same size as the others or smaller?
A smaller fish could indicate it has some sort of parasite or disease that is stunting its growth. Gill flukes would make it harder for a fish to breath and can slow the fish's growth. The Corydoras could be responding to this by taking air from the atmosphere to compensate for the breathing difficulties in the water.

Most catfish can breath air from the atmosphere. They swallow air and absorb the oxygen from it while it passes through their digestive tract. Then they fart the air out.
 
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Gypsum

Gypsum

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It's the same size as the others and looks okay on visual inspection.
 

Colin_T

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Any chance of a video and some pictures of the fish doing its thing?
If you have trouble putting the video here, upload it to YouTube and copy & paste the link here. We can view it at YouTube.
 

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