Rainbow Trout

Rainbow Trout, Oncorhynchus mykiss

The Rainbow Trout, Oncorhynchus mykiss, whose common Spanish name is trucha arcoiris, is a species in the Salmon and Trout or Salmonidae Family, known collectively as salmones and truchas in Mexico. Globally, there are 17 species in the genus Oncorhynchus, of which two are found in Mexico’s freshwater systems.

The Rainbow Trouts have fusiform bodies and a blue to olive-green coloration with a pink or red band extending along the body of fish found in freshwater. They have dark spots on their body, dorsal fin, and tail. Their adipose fin has a black edge. Coloration varies with habitat, size, and sexual state.

The Rainbow Trouts are a freshwater species commonly found in fast flowing streams and open lakes; they require high quality, unpolluted, and well-oxygenated water year-round. The Steelhead Trouts are a population of Rainbow Trout that are migratory, spend most of their lives in oceanic waters, and are found only in the Pacific Northwest. They reach 1.22 meters (4 feet) in length and 16.3 kg (36 pounds) in weight. Juveniles consume zooplankton and adults feed on aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fish. Reproduction occurs in fast-flowing well-oxygenated freshwater streams and rivers multiple times per year with eggs deposited in gravel bottoms. They reach sexual maturity in approximately two years and have a lifespan of eleven years.

In Mexico the Rainbow Trouts are found throughout the highlands of Central Mexico.

The Rainbow Trouts were introduced to Mexico at the end of the 19th century with formal farming commencing in 1937 and providing a product of high economic and nutritional value with local employment opportunities within rural communities. The optimal water temperature for egg development is between 8oC (46oF) and 12oC (54oF). They are fast growing reaching 0.5 kg (1 pound) in a year and 4.5 kg (10 pounds) in three years in captivity. They are highly disease resistant, can be fed artificial high protein high fat diets, and can tolerate different environments, thus are prime candidates for aquaculture. They are fed the synthetic pigments astaxanthin and canthaxanthin (yuk!) in aquafeeds to generate pink-colored meat. They are the focus of significant research on genetic manipulation and cross-breeding to improve growth rates, resistance to disease, prolificacy, and meat quality. In Mexico, production currently occurs in about 1000 individual farms in 15 Mexican states within the Sierra Madre Mountains with the largest production taking place in the states of Mexico, Puebla, Tamaulipas, and Veracruz. They are raised in raceways, ponds, and cages with recirculating systems. Mexico currently ranks 17th in global Rainbow Trout production. They do not reproduce in captivity and are sustained mainly with imported eggs which are prone to viral and bacterial infections. They have been genetically manipulated to reduce the “hook” shape of their jaw to increase consumer appreciation and to ensure that introduced individuals or escapees cannot reproduce. Fish are normally harvested in 7 to 12 months and generally weigh about three-fourths of a pound. They are marketed fresh, frozen or canned in fillets or whole and can be smoked or processed into breaded fillets. They can be found in the fine restaurants of Mexico City and are desired for their flavor, meat texture, high nutritional value, and low fat content; they are mostly consumed domestically with limited exports. They have a poor shelf-life and suffer from a negative public opinion related to genetically altered food. In the wild, their populations have declined significantly, generating strong conservation efforts. From a fishery management perspective there is concern that they will hybridize with the Mexican Golden Trout, Oncorhynchus chrysogaster. Globally they are heavily regulated and considered Endangered. Interestingly they are currently on the list of 100 most invasive exotic species in the world.

Note: this fish will show up occasionally in the fresh fish section of many major supermarkets in the greater Los Cabos area. They are always “old”, beat to hell with badly faded color, of very poor quality, and sold at high prices.

Rainbow Trout, Oncorhynchus mykiss. Commercial fish purchased at Wal-Mart, Cabo San Lucas, Baja California Sur, December 2012. Length: 32 cm (13 inches). The fish color is typical of a hatchery fish and the eroded caudal lobes are an indication of fish held in a raceway.