One would have to believe that very few species would not eat eggs, unless brood care comes from their nature. Primarily, some fish has injested food, broken down that food and excreted all the useless fillers and roughage and unuasable nutrients in the food -- not a terribly efficient process -- to make this egg. And you know the egg is full of good nutrients, as the fry have to live off the egg-sack for at least some time. So, to most fish, eggs are just about the best food ever.
And, of course, secondarily, many fish are gang spawners, with groups of 100s or 1000s mating at once, and nature takes over again; fish are compelled to eat others' eggs to give their own brood a slightly larger chance at surviving. In the aquarium, the fish don't realize that there are only 10s of them (or 1s!) and even though it is their own eggs present, nature still compels them to try to eat as many as possible.
And, of course, secondarily, many fish are gang spawners, with groups of 100s or 1000s mating at once, and nature takes over again; fish are compelled to eat others' eggs to give their own brood a slightly larger chance at surviving. In the aquarium, the fish don't realize that there are only 10s of them (or 1s!) and even though it is their own eggs present, nature still compels them to try to eat as many as possible.