Fish Disapeared Without Trace.

There are a couple of possibilities.
You have already discovered one - fish jumping out of the tank. Sometimes they end up down the back of the tank where you've got to look for them rather than just come across them, or possibly ending up inside a dog or cat if you have any of those.
Fish are very good at hiding - have you looked everywhere in the tank, including inside decor and the filter?
And living fish are very good at removing bodies. I have had fish disappear without trace including some biggish ones. Smaller fish are eaten faster, often within hours. I have on occasions found spines when I have been cleaning a tank, everything else has gone.
You don't say what other fish are in the tank, but I think this last one is the most likely scenario.

Thank you for your replies. I have no other pets so not that. Its only a small tank with fold down lid it would be easy to see any escapers. Also I noticed this before starting a water change making sure none were sucked up the pipe and into the bucket the ornament's are washed in the used water and checked with no trace of the fish or remains. There are 3 other fish with 3 black strips down and 3 with black pattern towards the tail. Could be an Alien encounter. 

Like Sue I've lost quite a few fish and never found the carcasses. Bodies degrade fast in tropical water and you might not even get an ammonia spike if the filter bacteria is hale and healthy and a dead fish becomes food to a lot of different species.

I lost an oto 4 days ago, couldn't see him anywhere...until today.