Host, seasonal and habitat influences on incidence of Lernaeenicus radiatus (Copepoda: Pennellidae) in the mid-Atlantic Bight

Lernaeenicus radiatus is a pennellid copepod with a 2-host life cycle that exhibits high host-specificity to their first host, black sea bass Centropristis striata. This parasite was prevalent in the gills of black sea bass juveniles and adults along the coast of New Jersey, USA, April to December 2019. Parasite incidence was high in the summer and fall in near-shore areas and dropped significantly in fish from deep waters further off-shore in December. Heavy infections of L. radiatus occurred in gills of adult black sea bass inhabiting reef-associated structures, in which parasite incidence rate was 2-3.7 times higher than in non-structure habitat. Less host-specificity occurred in second hosts which support female metamorphosis. In total, 7 fish species were confirmed as second hosts, with the most common being Atlantic menhaden Brevoortia tyrannus and bay anchovy Anchoa mitchilli. Incidence of L. radiatus depends on host abundance and habitats that support interactions of the preferred fish hosts, which may explain the heavy infections in reef habitats. The L. radiatus anchor process in metamorphosed females was highly polymorphic, depending on tissue tropism. Parasite length varied considerably, with neck and trunk measurements of L. radiatus from adult menhaden being 2-4 times larger than those from smaller host species. Mitochondrial cytochrome oxidase c subunit I (COI) sequences demonstrated all parasites to be L. radiatus, with sequence divergence limited to 0.3%. These findings show that morphology of the metamorphosed females has poor taxonomic value, and polymorphisms instead are related to attachment site and host characteristics.