Quantifying circulating antibody activities against the emerging environmental pathogen, Streptococcus agalactiae, in wild captured bull sharks, spotted eagle rays, bottlenose dolphins, and loggerhead turtles

•Streptococcus agalactiae is an emerging environmental pathogen in the aquatic environment.•Monoclonal antibodies were generated against bottlenose dolphin IgG and against spotted eagle ray and bull shark IgG.•A previously generated monoclonal antibody against loggerhead sea turtle IgY was used to compare marine vertebrate responses.•Relative antibody titers against S. agalactiae were quantified and compared to calculated antibody activities.•Calculated antibody activities are more sensitive than simply relative antibody titer data.