Rapid classification of nuclear cataracts lake trout

To examine lake trout (Salvelinus namaycush) in the field for cataract and noncataract eye abnormalities, we developed a procedure with a circular 1.7‐power illuminated magnifying lamp. A box in which the lamp is mounted facilitates its transport and provides a support base for the lamp during use in the field. A classification system was developed for assigning nuclear cataracts to four stages based on cataract size as a percentage of the total cross‐sectional area of the lens. When the method was used by newly trained technicians to screen 200,000 fall lake trout fingerlings into cataract and noncataract groups, the error rates were 1.7 and 7.7%, respectively. A technician could examine up to 2,800 fingerlings, 1,300 yearlings, or 700 3‐year‐old fish per day.