Annual dietary shifts of lumpfish (

Background: Lumpfish ( Results: Both morphological and DNA metabarcoding revealed significant differences in lumpfish diet composition across sampling years. Morphological analysis showed that 2018 was high for caprellid amphipods, krill, and "other"; 2020 was high for formulated salmon pellets and for ctenophore/cnidarians; and 2023 was high for caprellid amphipods and salmon pellets. DNA metabarcoding confirmed morphologically-identified species and enabled identification of soft-bodied and quickly-digested prey items, such as the salmon louse, to the genus and species levels. PERMANOVAs analyses of DNA metabarcoding showed that year explained 15.7% of variance at the genus level and 10.4% variance at the species level. Generalized Additive Models (GAMs) explained 64-84% of the deviance in temperature and 37.4% of the deviance in salinity, indicating that consistent seasonal environmental trends differed significantly among the 3 years. Conclusions: Changes in temperature and salinity were associated with variation in lumpfish diets across the three years, but additional annual surveys are needed to understand the mechanism. The highest summer seawater temperatures at 5 m occurred in 2023, the year when company SCUBA divers reported unusually low lumpfish survival in late October, and when the diets of those that remained alive contained no wild Norwegian krill. We suggest that rising sea temperatures may reduce the suitability of lumpfish as cold-water cleaner fish in southern Newfoundland. The continued deployment of lumpfish may require sea cage designs that provide access to deeper, and cooler water refuges. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1186/s44479-026-00008-x.