You were correct. They were hiding. I have no idea how as the pond is outside of my window where I can see into it most of the day and when I had mosquito fish which were the same size or smaller, I could see them okay in there.

I went to great lengths in the end to try to find those rainbow fish. Some may find this story funny.

I took every single plant and rock out of the pond. Caught all my frogs and took them out (that one wasnt easy!! Swamp frogs swim well). I then bucketed most of the water out and scrapped all the dirt from the bottom of the pond with a container and then later used my hand.. allowing all the sediment to sink again so I could see bottom fairly well. No fish at all were to be seen so I became completely convinced they were gone.

I refilled pond and put everything back in. 5 days later I suddenly saw two of the murray rainbow fish chasing each other!!! I couldnt believe my eyes. How on earth did they hide from my nearly emptying whole pond out to look for them?

Then cause I'd emptied the pond like I had.. I'd messed the pond up and it then developed for the first time ever, horrid stringy green slime algae which coated over some of my more delicate plants so killed them. It was getting so thick I was worried the frogs would get caught in this and I was pulling it up in big slime handfuls but it would quickly grow again. So Ive had a nightmare trying to get my pond back to how it was!

I brought new plants of the ones which previously growing great before this slime issue occurred as I'd ruined obviously some delicate pond balance.. but they died too due to the slime. Im only now just starting to get the pond good again (I ended up putting benefical bacteria into the pond, maybe that helped as its got better some again since). All these troubles just over some fish!!

Lesson learnt, some fish are very very sneaky. Today Ive found the murray rainbow fish have had babies, I havent seen their parents since but I trust they are there. (I'd better not have missed a mosquito fish which I removed about 6mths ago) and I have my first naturally got there tabpoles in the pond too (neither of those were there yesterday).

Anyway, if anyone has Murray River Rainbow Fish in a pond, do not expect to see these fish thou they are "supposed" to be surface feeders. (I guess only saw them just after I'd cleared out the pond spashing around at surface.. cause they would of had no wigglers left to chase due to me emptying water out and clearing out sediment at pond bottom).