Fig. 4.

Simplified diagram of purine nucleotide catabolism in fish, resulting in production of hydrogen peroxide (H₂O₂) that can be: (1) reduced to H₂O by glutathione peroxidase given adequate glutathione SH:SS ratio maintained by the pentose phosphate pathway, or (2) used to oxidise haemoglobin to methaemoglobin molecules that link to form Heinz bodies, modified from Sanchez-Muniz et al. (1982) and Berg et al. (2015)