Salmon Cataract Welfare in Aquaculture

Cataracts affecting sight in farmed salmon cause chronic welfare harm and are a widespread industry problem with identified nutritional solutions.

Key Facts

Cataracts affect over 80% of farmed Atlantic salmon in many operations, causing progressive vision impairment and blindness
The primary cause is deficiency of the amino acid histidine during smoltification — an identified and preventable nutritional problem
Blind salmon cannot compete effectively for feed, suffer reduced food intake, and display abnormal behaviour patterns
Navigation difficulties in blind fish cause repeated collisions with net pen infrastructure, causing physical injury
Histidine-supplemented diets during the smoltification period dramatically reduce cataract prevalence in preventive protocols
The welfare cost of widespread industry cataract prevalence represents millions of fish living with preventable disability

Welfare Considerations

Salmon cataracts represent one of the clearest cases in aquaculture where a major welfare problem has an identified solution that is not universally implemented. Histidine deficiency during the metabolically demanding smoltification period allows lens crystallin proteins to aggregate, producing the opacification of cataracts. The nutritional correction — histidine supplementation in smolt feed at the critical developmental period — is relatively simple and proven. Yet cataract prevalence remains high across the industry, indicating that the economic incentive to implement preventive nutrition does not yet outweigh the cost for many producers. The welfare case is compelling: blindness in a visually dependent predator causes chronic disadvantage, injury risk, and likely negative affective states. Welfare-conscious certification schemes increasingly specify cataract monitoring as an outcome indicator.

What You Can Do

Support salmon certification schemes that include cataract prevalence monitoring as a welfare indicator requirement
Advocate for mandatory histidine supplementation standards in salmon smolt feed as a welfare intervention
Choose salmon from operations that publish cataract prevalence data as part of their welfare transparency reporting
Back research into other nutritional factors affecting cataract development in farmed salmon
Support welfare education for aquaculture nutritionists about the preventability and welfare significance of salmon cataracts