Tropical fish include fish found in tropical environments around the world, including both freshwater and salt water species. Tropical fish are popular as aquarium fish, due to their often bright coloration. In freshwater fish, this coloration typically derives from iridescence, while salt water fish are generally pigmented. Fishkeepers often use the term tropical fish to refer particularly to those requiring fresh water, with saltwater tropical fish referred to as marine fish. Tropical fish kept for home aquaria include the following: Wild-caught specimens. Single-species individuals born in captivity. The latter category includes lines selectively bred for special physical features, such as long fins, or particular colorations, such as albino. Hybrids of more than one species. Recreational SCUBA divers are often enthusiasts of tropical fish as well. Some keep lists of fish species they have observed while diving, especially in tropical marine environments.