Thiamine (
vitamin B1) is required by all living organisms in multiple metabolic pathways. It is scarce in natural systems, and deficiency can lead to reproductive failure, neurological issues, and death. One major cause of
thiamine deficiency is an overreliance on diet items containing the
enzyme thiaminase.
Thiaminase activity has been noted in many prey fishes and linked to cohort failure in salmonid predators that eat prey fish with
thiaminase activity, yet it is generally unknown whether evolutionary history, fish traits, and/or environmental conditions lead to production of
thiaminase. We conducted literature and GenBank BLAST sequence searches to collect
thiaminase activity data and sequence homology data in expressed
protein sequences for 300 freshwater and marine fishes. We then tested whether presence or absence of
thiaminase could be predicted by evolutionary relationships, trophic level,
omega-3 fatty acid concentrations, habitat, climate, invasive potential, and body size. There was no evolutionary relationship with
thiaminase activity. It first appears in Class Actinoptergyii (bony ray-finned fishes) and is present across the entire Actinoptergyii phylogeny in both primitive and derived fish orders. Instead, ecological factors explained the most variation in
thiaminase: fishes were more likely to express
thiaminase if they fed closer to the base of the food web, were high in
polyunsaturated fatty acids, lived in freshwater, and were from tropical climates. These data provide a foundation for understanding sources of
thiaminase leading to
thiamine deficiency in fisheries and other organisms, including humans that eat uncooked fish.