Thankyou will try these things... I have just seen him leave this position/state and act semi-normal, following the other silver shark swimming together etc (this is what they usually do) and then return to the exact same position and just do what it was doing before, slight movements of its...
Have a 134L tank with under 20 fish - tanks been setup for 3-4 months, temperature is correct.
The fish in question is a silver shark (not sure if that’s the official species name)
It isn’t young or small and is in the tank along with a similar sized fish of the same species, they were...