Macroscopic intersexuality in salmonid fishes

Abstract

Abstract The occurrence of individual salmonids with macroscopically identifiable, simultaneous male and female gonads is an uncommon reproductive disorder. Individual specimens have been described, but no larger synthesis of the condition has been made. We first describe two simultaneous in‐tersexual Pacific salmon ( Oncorhynchus spp.) specimens, encountered during rearing operations in New Zealand and Chile, confirming that the phenomenon occurs beyond the natural range of the genus. A review of these and other isolated specimens within the Salmonidae ( Oncorhynchus, Salmo, Salvelinus, Coregonus, Thymallus ) suggests that the disorder takes at least two distinct anatomical patterns, which we call lobular and mosaic. These are consistent with differences in either the degree or onset time of aberrant development from protogynous or neutral gonadal primordia. The disorder has a low natural incidence (one in several thousand), but the extensive use and study of salmonids makes it likely that natural macroscopic hermaphrodites will be encountered regularly. Isolated specimens have been attributed to environmental contamination, but their widespread occurrence suggests they are primarily a natural phenomenon.