Chronic CO2 exposure markedly increases the incidence of cataracts in juvenile Atlantic cod Gadus morhua L.

A study was undertaken to test the affect of chronic exposure to elevated dissolved carbon dioxide on juvenile Atlantic cod. The CO2 treatment concentrations were designated as low (1–2 mg L− 1, 1000 μatm), medium (8 mg L− 1, 3500 μatm) and high (18 mg L− 1, 8500 μatm), and the fish were reared at 10 °C and 20‰ salinity. A marked observation at the end of the 55 day trial was that an increase in the incidence of eye lesions correlated with increasing CO2 concentration. Typical lesions included unilateral and bilateral exopthalmos, gas bubbles under the sclera and cataracts, and these were quantified in all fish (n = 757 individuals) using field methods. The most notable difference between CO2 treatments was the prevalence and intensity of lenticular cataracts, which were primarily diffuse rather than nucleated. Nearly 75% of all fish from the high CO2 treatment were found to have some degree of cataractous lesion, compared with 10–13% for the other treatments. The severity of the cataract was most pronounced at the highest CO2 concentration, with many fish presenting complete bilateral cataracts. These data indicate that chronic exposure to high CO2 concentrations can cause cataracts in juvenile Atlantic cod. To our knowledge this is the first report of CO2 as a causative agent or aggravating factor for cataracts.

► Juvenile Atlantic cod were exposed to three CO2 levels for 55 days.
► Cataract severity was much higher at 18 mg L− 1 CO2 compared to lower CO2 levels.
► This is the first report linking elevated CO2 exposure to lenticular cataracts.