U.S. tilapia farmers generally raise tilapia in low-risk, closed re-circulating systems (Goldburg and Triplett 1997; Fitzsimmons, pers. comm., 2006). Since tilapia are tropical fish, farms in colder regions must use water heated by geothermal processes or by the waste heat from industrial sources (USDA 1995; Boyd 2005).

In some southern states, some farmers raise tilapia in cages located in ponds (Fitzsimmons, pers. comm., 2006). However, the great majority of U.S. tilapia farms use re-circulating systems, so we chose to award a high score of 3.00 points here.

Tilapia raised in re-circulating systems are stocked at high stocking densities (AU and USDA 2004).

Some southern tilapia producers use polyculture techniques in their operations, in which they stock tilapia with catfish or with shrimp and algae (Williams 2000; Fitzsimmons 2001). Raising strategically selected species together can help reduce the amount of nutrients and waste in the system and in the effluent. Only a few farms, however, use this innovative method, because fish sorting at harvest requires more time and energy and raises production costs (Williams 2000). Therefore we chose to not award points for this factor.

States regulate the siting of farms (Fitzsimmons, pers. comm., 2006).

Although tilapia are herbivorous and can survive on a plant-based diet, tilapia farms use feed that contains as much as 8% fishmeal (Boyd 2005). However, this high-fishmeal feed is reserved for fingerlings (Boyd 2005), while adults typically receive feed containing 5% or less fishmeal (Goldburg and Triplett 1997; Fitzsimmons, pers. comm., 2006).

Fish products constitute less than 8% of tilapia feed (Boyd 2005).

Feed conversion ratios (FCRs) in tilapia aquaculture vary depending on several factors, including fish size, water temperature, and amount of fishmeal in feed (Boyd 2005; Fitzsimmons, pers. comm., 2006). Typically, FCRs range between 1.7 and 1.9 for farmed tilapia (Fitzsimmons, pers. comm., 2006). Since these ratios are higher than 1.3, we chose not to add here.

Since tilapia are stocked at a high density and intensively fed, wastewater from tilapia farms is high in nutrients, organic matter, and suspended solids, making its treatment an important environmental concern (AU and USDA 2004). The U.S. Environmental Protection Agency requires fish farms to hold National Pollution Discharge Elimination System permits. These permits require them to minimize their discharge of chemicals and excess feeds, maintain water treatment systems, keep records of operations, and develop and implement best management plans (EPA 2004). Since tilapia farms in the U.S. typically use low-pollution re-circulating systems, which re-circulate water and release only small amounts of effluent (Goldburg and Triplett 1997; Fitzsimmons, pers. comm., 2006), we chose to award a high score of 3.00 points here.

Tilapia are resistant to most diseases; therefore, farming tilapia species rarely, if ever, requires the use of antibiotics, drugs, and other chemicals (Boyd 2005).

The Environmental Protection Agency strictly regulates wastewater treatment at tilapia farms with the Clean Water Act's National Pollutant Discharge Elimination System permit program (EPA 2004).

Tilapia are not native to the U.S. and are a threat to native freshwater fish. They reproduce quickly, eat the eggs and juveniles of other fish species, and caused the endangerment of native fish species in the lower Colorado River, where they were intentionally introduced to control aquatic vegetation (Fitzsimmons 2001).

Because of this apparent risk of tilapia farming, the majority of tilapia farms in the U.S. use closed re-circulating systems and are located in areas where tilapia have already become established in nearby rivers and lakes or where cold winters kill escapees (Boyd 2005; Fitzsimmons, pers. comm., 2006). Some tilapia farmers in southern states raise tilapia in cages located in ponds, however. We chose to award a medium score of 2.00 points to account for tilapia being non-native and for the higher-risk pond operations for tilapia aquaculture.

The establishment of non-native tilapia in the rivers and lakes of the U.S. is well documented (Canonico et al. 2005). Tilapia can survive in poor water conditions, moderate salinities, and are resistant to disease. In addition, they mature as early as 2 months old and reproduce year-round. These characteristics enable tilapia to thrive in environments in which they are not native (Boyd 2005).

Prior to tilapia aquaculture in the U.S., tilapia were imported to control aquatic weeds in irrigation canals. They escaped from these canals and now dominate the fish fauna of the lower Colorado River system, endangering native fish species (Fitzsimmons 2001; Boyd 2005).

Tilapia are voracious eaters and compete with native fish species for food (Fitzsimmons 2001). Although generally herbivorous, tilapia also feed on the eggs and young of other fish species native to an area (Boyd 2005; Canonico et al. 2005).

Incidence of disease in tilapia farms is low (Boyd 2005).

Open-pond tilapia farms are banned in much of the U.S. due to the ability of tilapia species to establish breeding populations in new environments (USDA 1995; Fitzsimmons, pers. comm., 2006). For this reason, most U.S. tilapia production occurs at farms using closed re-circulating systems (USDA 1995). In addition, states regulate site locations for new farms, as well as and stocking practices for tilapia (Fitzsimmons, pers. comm., 2006).

Tilapia farms in the U.S. are most often located in areas currently or formerly used for agriculture (Williams 2000).

Re-circulating systems isolate tilapia from potential predators; therefore, predator deterrents are unnecessary at the majority of U.S. tilapia farms.

Hatcheries that use domesticated stocks supply seed to all U.S. tilapia aquaculture operations (Fitzsimmons 2001; Fitzsimmons, pers. comm., 2006).