Age Validation of Monkfish

Monkfish, Lophius americanus, are an important component of commercial fisheries in the Northeastern United States, but assessment of this species is less reliable due to uncertainties with age determination.  Vertebral growth rings are presumed to follow an annual pattern and are counted to estimate age.  However different calcified structures, illicia and otoliths have been used to age other Lophius species.  To validate the vertebral ageing method, monkfish were injected with a chemical marker, oxytetracycline or fluorexon, and reared for a year in the laboratory while being subject to seasonal cycles of temperature and light. Wild-caught monkfish were also injected and released as part of a data-storage tagging study.  The injected chemical marks the growth ring that is forming at the time of injection and is visible under ultraviolet light. Vertebrae, illicia, and otoliths were sampled from fish that lived six months or more after injection (both laboratory and field), and digital images of these structures were captured under ultraviolet light.  Annuli were counted in reflected light and compared with the marked image.  Results did not validate the vertebral ageing method, nor were annual rings identifiable on otoliths. Therefore, the illicia ageing method should be explored further for this species.