Metabarcoding demonstrates dietary niche partitioning in two coexisting blackfish species

A problem for fisheries ecologists who carry out dietary analysis on their specimens is dealing with contents that are difficult to identify, particularly when the contents comprise digested prey. We used a DNA metabarcoding approach to determine the diets of two co-occurring black fish species (Gadopsis bispinosus and Gadopsis marmoratus) to circumvent any issues with trying to apply microscopic methods to identify diets. We examined the frequency of occurrence of taxa across all specimens and the proportion that taxa contributed to total diet. In this way we hoped to demonstrate that a DNA-based method could resolve dietary differences of coexisting taxa. We showed that 10 macroinvertebrate taxa dominated the diets of both species and, of these, 7 occurred in all specimens of both taxa, indicating they were an important component of the diet of both species. Twelve taxa were present only in the G. bispinosus diet and four of those were terrestrial invertebrates; six taxa were found only in G. marmoratus. Our DNA-based approach to examine the taxa in the guts of two co-existing Gadopsis species provided sufficient resolution to show a significant degree of dietary partitioning.