Mirror, mirror, on the tank

[Lynnzer]

Why the hell do fish seem to swim endlessly up and down the glass?
Can they see their reflection and try to join with it, or are they trying to pass across into the adjoining tank?
Perhaps they're eating algae off the glass as they swim up and down?

 

[I Like Rare Fish]

It’s called ‘glass surfing’. My Senegal Bichir, the most active Bichir, glass surfs often. He is a carnivore, so not eating algae. I’m sure someone will post some science article BS about studying fish who glass surf, but in my opinion they’re trying to find what is outside, or explore their territory.

 

[Colin_T]

Sometimes because they see their reflection and either want to kill it (male betta splendens), or school with it (tetras).

Other times they are new to the tank and can't work out how big it is. So they move along the glass for the first few days trying to work out why they can't go through the invisible wall. This can be reduced by having algae on the back and sides of the tank.

 

[Lynnzer]

The mirror, mirror bit is derived from an earlier experience.
I was keeping about half a dozen Odessa Barb and one of them was so damned annoying. He couldn't stand any other fish coming anywhere near him and bullied the hell out them.
I stuck a small makeup mirror on the front of the tank so that when he passed, he saw himself.
He tried like hell to kill himself and in the end he backed off and calmed down a lot. I think he became subservient to his own reflection

 

[jaylach]

Depending on the lighting outside of the tank the glass can act as a one way mirror. This is true with glass, don't know about acrylic. this will normally occur when the room's ambient light is less that that of the tank.

 

[Deleted member 149562]

When I first transferred my fish from their small aquariums into the larger one, there was alot of glass surfing. It was quite funny tbh cos each surf they ventured further and further down the length of the aquarium. Once they figured out that their puddle had turned into a lake, they pranced about all over all 4 sides for hours at a time.

Now though some of them have discovered the TV that is near to one end of the aquarium and they jockey for the best spot to watch the TV.....many are transfixed by the colour changes and movement off the screen (it is about 4ft away from them).....my surfing dudes and dudettes have turned into telly addicts

 

[Sgooosh]

After more thAn a year the cories still sometimes do it. Think they are trying to eat stuff in the 4th dimension

 

[Byron]

In the majority of cases, glass surfing is a sign of stress. This came up in my discussion with Neale Monks the other day over the thread about fish emotions. Neale said that many think cories and other fish are "playing" and having fun, but it is a sign of stress. Newly introduced fish often do it but not beyond maybe a few days, as they settle into their new environment. After all, how would any of us feel if someone picked us up and plunked us down in a totally different environment. This is especially problematic if the environment (water parameters, habitat features, other fish) is not what the fish expects.

 

[lottabubbles]

could be a fish is looking for a way out of there

 

[outofwater]

Neale said that many think cories and other fish are "playing" and having fun, but it is a sign of stress.

Besides the stress situation, does this happen specifically with female cories when they're about to spawn?

Those are the only ones (that I own) who seem to do it every other week, then they calm down for the next week, then I see it ramp up again. Or when they're hungry. There are days when these girls won't stop patrolling the entire tank searching for something to eat.

 

[Byron]

Cories will rapidly swim up the glass sides of the tank when spawning, but you would see one or more males with the female.