My dad built a fishpond 3 years ago and has had fish in there ever since.  About 3 months ago they all disappeared and thought that the cats or a bird must of taken them away.  Well last week, 3 popped up and were swimming around and they've now disappeared again,  could they be preggers or is there any other reason for this.  The pond isnt very big but my mum said that the 3 that re-appeared had really grown.

Hi Diane, whats the temp like where you are.  Its still quite cool here and my lot are only just coming to the surface now.  I just started feeding them again around April. My goldfish come to the surface earlier than the Koi, who have only just started to rise. But they do prefer to be deeper that the others, and they have nearly doubled in size from last October.  My fish produced babies last year around August/September but they did not survive the winter. The females may be carrying eggs, so watch for the fun of fertilisation, its fascinating.  During the summer the fish were really playfighting and rubbing against each other at the surface of the water, the males fertilising the female eggs.  It is very noticable and goes on for days, at least it did with my lot. I love wasting time pondwatching.  But it would all depend on the weather temp and the temp of the water.

What type of fish do you have?  I have Ghost Koi, goldfish, Silver Orf, and Green Tench, 5 newts 3 frogs and the odd toad as a visitor

Second that, they're probably just starting to get active again.  Mine have been out and about for a few weeks, but even now they're quite secretive.

What's the plant situation like in your pond?  I find my fish will swim around much more when the plants are in full swing, especially with plants like water lilies that spread over the surface, gives them something to hide under.  As Kayc said, if your fish were spawning you'd actually see more of them - the males can get very enthusiastic in chasing the females, regardless of who's watching!

It could be that whatever took some of the fish ahs made them wary - fish aren't as dim as most people think, they learn and remember things (especially big hungry things!!) quite well.  I've seen less of my fish since my brother's cat moved in 2 years ago and ate half of them!!

Your pond sounds nice Kayc, going by the populous - I've got golds and shubunkins in mine of all sizes (not big enough for orfe or koi, sadly - garden too small!), as well as half a dozen frogs (some froglets also :) ), about 20 newts and for summer, a common pleco from my big tropical tank.

I'll go with what's said.
I've a 9 acre lake and the carp go crazy early spring time when the water warms up. Unfortunately many of them are false spawning as the temperature of the water is fairly critical.
Your fish will gain weight over the summer months and will use the energy they gained to survive the colder months. They prefer the deeper water due to thermal layers and once the water warms up they became more active.
Carp need large ponds to survive and the larger they grow the more chance you have of fatalities as the oxygen levels drop. A thunder storm can mean disaster if the conditions are poor so a good aerating weed or a pump system will help them through the summer.
The off spring tend to get eaten by the parents as well and clear ponds with no weed will not be ideal conditions for the fry to survive.
Koi are a member of the carp family but where common, leather and mirror carp are hardy, Koi tend to be less hardy due to the genes which have been messed about to produce the colours.
I've 30lb plus carp in my lake along with large tench, perch, roach, rudd and pike. When they do spawn in their hundreds they totally wipe out some of the reed beds around the lake and if you're careful you can almost touch them in the shallows.
If you feed your fish on a daily basis they will became accustomed to you and will in the end take the food from your hand. Trout pellets are great for this as they contain a good level of proteins and this will help them gain weight for the cold weather.
Word of warning, there are some diseases that target carp and the result is awful. If you own Koi and wish to add more make sure you get them from a recognised source which will help cut down the chance of infection. Unfortunately about 10 years ago some one put their gold fish in our lake which resulted in a parasite infection. Also the carp cross bred resulting in some weird looking goldfish.