Detached tentacles of lion’s mane jellyfish Cyanea capillata can injure aquaculture fish

Abstract

Gelatinous zooplankton can cause fish mortalities and economic losses for aquaculture companies. While protective measures against jellyfish blooms are increasingly implemented, free-floating tentacles have not been considered. Tentacles with active cnidocysts, both whole and fragmented, can cause potential damage to fish for an unknown duration after the jellyfish bloom has passed. In this pilot study, we measured for how long detached tentacles of the lion’s mane jellyfish Cyanea capillata can cause injuries/catch zooplankton prey. Controlled experiments were conducted in late summer 2007 using in situ collected specimens from northern Iceland. Jellyfish tentacles maintained their full ability to capture brine shrimps Artemia salina for 24 d. However, no prey could be immobilised from Day 26 onwards. To our knowledge, this is the first experimental evidence showing how long cnidocysts in tentacles can catch prey and thus potentially harm aquaculture fish after detachment (about 3.5 wk); this information should be considered when making any hypothetical risk assessment.