On iGoogle fish aquarium why do some fish disappear the next day?

In the igoogle fish aquarium, some fish may disappear the next day due to a few possible reasons. One common explanation is that they might have "died" due to neglect in their care or environmental conditions, such as poor water quality. Additionally, the game could have a built-in mechanic where fish randomly disappear over time to simulate a dynamic ecosystem. Lastly, if the user doesn't visit the aquarium regularly, fish may vanish as part of the gameplay design.