These are a shelter designed for shrimp to sneak into to evade fish and feel safe. Caution should be used with fish such as bettas as they can try to fit into the holes and could become stuck. Don't mix with fish where that could pose a problem. Most all other community fish would be fine with these shelters. Can also be used to get a moss shelter going as well by putting moss under the shelter and letting it grow through the holes. The shrimp shelter measures 2 inches wide by 1 inch tall.