Fishkeepers often keep tropical fish in freshwater and saltwater aquariums. Ponds may be freshwater, saltwater, or brackish. It is an area rich in shellfish, freshwater fish and saltwater fish. Estuaries form a transition zone between freshwater river environments and saltwater maritime environments. Egrets hunt and live in both saltwater and freshwater marshes. Pearls can form in both saltwater and freshwater environments. Fisheries can be marine (saltwater) or freshwater. Breeding for freshwater species is more advanced than for saltwater species. Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They can be saltwater or freshwater, wild or farmed. There is strong biological diversity, including intertidal vegetation like freshwater cattails and saltwater cordgrasses. Estuaries occur where there is a noticeable change in salinity between saltwater and freshwater sources. These freshwater algal blooms should not be confused with those in saltwater environments. Tony is seen many times throughout the show engaging in both freshwater and saltwater angling. Ponds may be fresh, saltwater, or brackish.