|Gobies are small elongated fishes with rounded or depressed heads. Eyes are usually on top of their head and close together. The pelvic fins in most are fused together to form an adhesive disk. Males and females may differ in coloration and body patterning. This family contains the largest number of marine fishes. It also contains the smallest fishes in the world. Some species form symbiotic relationships with other fishes and invertebrates. They live in the shallow Gulf, estuaries and sometimes freshwater. Some species are catadromous (live in freshwater but migrate to saltwater, usually to spawn). They live on soft mud substrates but also can be found around reefs and other hard substrates. These are popular aquarium fishes.