I was gifted this tank but it came without a power socket, I need the right kind of fitting to connect it to the power source
That is a socket.
Looks like a standard barrel connector.
There should then be a plugpack/wall wart that plugs into the mains with a matching barrel plug on it's lead.
Most will have that type of connector or swappable tips, including that one. It is by far the most common type and typically positive on the pin, negative on the outer ring.
You need to figure out the voltage and current draw though. Check for a label on the light, if there is an actual globe there may be markings for power and voltage.