Aquaculture Salmon Cataracts and Welfare

Cataracts are a significant welfare and production problem in farmed salmon with established nutritional causes and preventive solutions.

Key Facts

Cataracts affect up to 80-100% of farmed Atlantic salmon in some production cycles, particularly at high water temperatures
Histidine deficiency is the primary nutritional cause, with plant protein diets displacing histidine-rich marine ingredients
Cataracts cause progressive vision loss that impairs feeding efficiency, schooling behavior, and predator avoidance responses
Blind or visually impaired salmon show reduced growth rates, increased stress responses, and higher injury rates during handling
Supplementing feeds with adequate histidine (minimum 0.6% of dry matter) essentially eliminates nutritionally induced cataracts
UV-B radiation from sunlight exposure in surface net pens contributes to cataract development alongside nutritional factors
The Norwegian salmon industry has made significant progress in reducing cataract prevalence through nutritional standards

Welfare Considerations

Salmon cataracts represent a welfare problem with an identified cause and a known solution, yet prevalence remained unacceptably high for decades due to economic optimization of feed composition that prioritized cost reduction over welfare. Vision is critical for salmon in multiple behavioral dimensions: feeding (salmon are visual predators), schooling (visual coordination with conspecifics), and predator detection. Visually impaired fish show measurable changes in feeding behavior, schooling dynamics, and stress responses that indicate reduced welfare relative to sighted conspecifics. The solution — ensuring adequate dietary histidine — adds minimal cost to feed and has been shown to effectively prevent cataracts when implemented. Regulatory standards requiring minimum histidine in salmon feeds would eliminate this welfare problem across the industry, though progress through voluntary nutritional standards has been significant in leading-producing countries.

What You Can Do

Purchase salmon from producers in countries with advanced nutritional standards like Norway that have reduced cataract prevalence
Support research into UV-B protection for surface net pens as an additional cataract prevention measure alongside nutrition
Advocate for minimum dietary histidine standards in aquaculture feed regulations as a straightforward preventable welfare harm
Support alternative protein development for salmon feeds that maintains essential amino acid profiles while reducing dependence on wild fish meal