Demersal fish were sampled over 3 years to describe sealwormPseudoterranova decipiensinfection levels in relation to the size of a local colony of common sealsPhoca vitulinain Hvaler, Oslofjord, Norway. More than 2000 fish were examined for worms, and five fish species were found to be infected, codGadus morhua, four‐bearded rocklingEnchelyopus cimbrius, plaicePleuronectes platessa, long rough dabHippoglossoides platessoidesand dabLimanda limanda.A detailed analysis of worm accumulation in cod, the only infected species present in large enough numbers, shows a net decrease in worm transmission following the phocine distemper virus epizootic which killed two‐thirds of the seals in Hvaler in 1