Siamese fighting fish
Sleep behavior

Betta fish can exhibit unusual sleep behaviors, often resulting in new betta owners assuming that their betta fish has died. In an aquarium, betta fish sleep anywhere in the tank they feel comfortable, including at the bottom on the substrate, floating at the mid-level, or at the surface. Betta fish will sleep on their side, upside down, with their nose pointing up, or with their tail pointing up. They are also known to curl up or wedge between tight spaces, such as behind a heater. One of the more unusual sleep behaviors that betta fish exhibit is their ability to sleep out of the water, resting on a leaf or any other flat object protruding from the water. This is made possible by the betta's labyrinth organ, which acts like a human lung, pulling oxygen from the air instead of from the water. When betta fish sleep, their bright colors will often fade, and when combined with their unusual napping positions, they can appear dead. Predatory fish will often avoid eating a dead fish because of the risk of contracting diseases and parasites, making this an excellent defensive mechanism.
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