A stinging tale? Looking for Catostylus jellyfish nematocysts in the gills of trawled-and-discarded fish in southeastern Australia

Nematocyst cells ejected by gelatinous zooplankton (e.g. cnidarians and ctenophores; ‘jellyfish’) are harmful for many organisms, including humans. Despite more frequent blooming events in warm, productive coastal waters, the effects of nematocyst cells on wild-fisheries catches remain understudied in Australia and elsewhere. During a study to maximise the survival of discarded bycatch from penaeid trawls in New South Wales, Australia, jellyfish (Catostylus spp) in the catch (between 16 and 80% by weight) had a significant, deleterious effect on the survival of surf bream (Acanthopagrus australis), Castelnau’s herring (Herklotsichthys castelnaui) and common silver biddy (Gerres subfasciatus). Further, surviving surf bream showed a positive relationship between their blood glucose and potassium concentrations and the abundance of jellyfish in catches. During a subsequent study, gill histopathology on trawl-caught surf bream identified sloughing and congestion of tissue, but no nematocyst cells. However, this result may reflect relatively low catches of jellyfish.