such as different sizes of drumming muscles and pectoral spines. Due to these constraints, some fish may not even be able to produce a specific sound. In several different species of catfish, aggressive sound production occurs during cover site defense or during threats from other fish. More specifically, in long-whiskered catfish, drumming sounds are used as a threatening signal and stridulations are used as a defense signal. Kaatz investigated 83 species from 14 families of catfish, and determined that catfish produce more stridulatory sounds in disturbance situations and more swimbladder sounds in intraspecific conflicts. Economic importance Aquaculture Catfish are easy to farm in warm climates, leading to inexpensive and safe food at local grocers. About 60% of U.S. farm-raised catfish are grown within a 65-mile (100-km) radius of Belzoni, Mississippi. Channel catfish (Ictalurus punctatus) supports a $450 million/yr aquaculture industry. The largest producers are located in the Southern United States, including Mississippi, Alabama, and Arkansas. Catfish raised in inland tanks or channels are usually considered safe for the environment, since their waste and disease should be contained and not spread to the wild. In Asia, many catfish species are important as food. Several airbreathing catfish (Clariidae) and shark catfish (Pangasiidae) species are heavily cultured in Africa and Asia. Exports of one particular shark catfish species from Vietnam, Pangasius bocourti, have met with pressures from the U.S. catfish industry. In 2003, The United States Congress passed a law preventing the imported fish from being labeled as catfish. As a result, the Vietnamese exporters of this fish now label their products sold in the U.S. as "basa fish." Trader Joe's has labeled frozen fillets of Vietnamese Pangasius hypophthalmus as "striper." There is a large and growing ornamental fish trade, with hundreds of species of catfish, such as Corydoras and armored suckermouth catfish (often called plecos), being a popular component of many aquaria. Other catfish commonly found in the aquarium trade are banjo catfish, talking catfish, and long-whiskered catfish. Catfish as food Catfish have widely been caught and farmed for food for hundreds of years in Africa, Asia, Europe, and North America. Judgments as to the quality and flavor vary, with some food critics considering catfish excellent to eat, while others dismiss them as watery and lacking in flavor. Catfish is high in vitamin D. Farm-raised catfish contains low levels of omega-3 fatty acids and a much higher proportion of omega-6 fatty acids.