Predators is the first thing that crossed my mind too. I haven't lost any of my pond fish, but whenever I've lost fish in the aquarium, they typically float or get caught in the filter's uptake tube.

When a heron takes fish, there usually isn't any indication that they were there, except for the missing fish. My pond was uncovered until I saw a heron standing on the ground in a park a mere block away, and immediately put a net over the pond. I would much rather leave it uncovered, but it really doesn't look that bad.

Speaking from experience, in a large lake I have seen some dead fish submerged up to several feet (bottom depth being 10 feet and more). They looked intact, but bleached out, so were not freshly dead. I don't know what sort of 'cycle' or changes a fish carcass in water goes thru, but perhaps at some stage they do sink, or maybe only after they decompose some. Once at the bottom of a lake, the other critters would clean up the remains - part of life's food chain.

What I mean is, maybe if a dead fish were hidden by a lily pad or something it might go unnoticed for a day or two and then sink.

Just a thought, but I'd be worried about predators too. Either way, sorry about your fish.

Disappearing fish are likely due to a predator taking them from the pond. Sorry you lost your fishies.

As far as a deceased fish floating? It depends largely on the cause of death, water temperature and time of death before being discovered in the water.

If the cause of death was a swim bladder issue then the fish likely will float at the time of death. If the fish died of other causes it likely will sink initially and as the bacteria within the GI system and other internal structures multiply gaseous by products of their increased population and tissue decay will cause the deceased to float. After a time there will be a release of some of the gaseous by products and the corpse will again sink.

The time it takes for the deceased to rise to the surface will greatly depend on the size of the body as well as the temperature of the body of water in which it lies. Smaller fish + warmer water = faster rise and subsequent decent as decay progresses.

C3D

I was losing fish right and left to herons and racoons until the plants got big enough to hide them. It was a new pond and the plants hadn't filled out. We recently put in a second pond and this time I waited until there was a good amount of plant growth before putting fish in. If they did die I wouldn't worry about finding much of anything left of them when you clean the pond.
Karyn

Im having the exact same problem. I have two small backyard ponds where ive had six goldfish thrive in for two years. And they were healthy and fairly big. I also had a number of mosquito fish that were multiplying rapidly. About a month ago i went out to do my usual feeding and the goldfish were gone. As well as a large number of mosquito fish. Ive never seen a heron anywhere near my neighborhood nor a raccoon. I live in the eastern suburb of los angeles btw. Now i could possibly believe that a predator may have taken my goldfish. Although there were no sings of any prints on the surrounding sand. But why are my mosquito fish disappearing? Theyre really small, very fast swimmers and i have tons of plants and broken pots submerged for them to hide in. Im baffled with this.