Your fish is sick.. VERY sick...
Make sure you start doing regular water changes, at least every couple of days til your fishy friend gets better. As mermaid suggested, make sure you have oxygen going into your tank as well as using water conditioner when doing water changes.
You could use MELAFIX to medicate the tank however one drop of tea tree oil works exactly the same. If you add one drop of tea tree oil and tap water conditioner to a couple of litres of water, then put the new water in the tank, he should liven up a bit.
Hope this helps,
Lauren
