I agree with the other ladies here - the fish is dead, don't say anything else.

I'm open with my DS; I'm aware that no-one he knows is likely to drop dead soon and so I'll point out hearses in the street (along with tractors, diggers, busses, lorries, cars... all the usual!) and say that someone has died now and that means they're not on this earth any more, but we'll probably meet them again in the next life.

Death doesn't hurt, it isn't scary, it is just the end of life in this world - we have the next one to look forward to and that will be better because it will be with God.

As for experts (just my own bone to gnaw now...) - my granddad died when I was about 6 and I remember that clearly, remember being told, knowing what it meant. He'd been very ill with leukaemia for the last few months and we'd known he wasn't going to make it, so we had loads of time to have this explained to us. So some children may not get death until 8-9, others will understand earlier. Don't rely on experts whom have never met you tell you about your child's understanding.