One of my clients rang me in distraught. Soon after installing a wave maker, his magnifica anemone that had made a home for itself and hadn’t moved from the one spot for nearly a year, decided to “walk”. And walk it did, but only briefly until it encountered the powerhead and minced itself in the propeller blades. Within 4 hours, all fish species in the tank started becoming ill and died. The clinical signs they presented include listlessness, respiratory distress and death.
This reminded me of a case in aquacultured fish during my time working as a veterinary fish pathologist in a state veterinary laboratory. Usually, the netting used for aquacultured fish become fouled with aquatic organisms, and they are regularly taken ashore to be pressure cleaned and dried before re-use. But one time, the management thought it would save time and money to pressure clean the nets in-situ. But soon after this was done, high mortalities began to appear. Those fish that were affected were moribund and showed respiratory distress. Microscopic analysis of the organs of the fishes showed widespread, multiple pin-point skin and gill damage as well as severe splenic and liver damage. Such a pattern of damage was similar to previously reported cases of jellyfish stings. In this case of aquacultured fish, it was discovered that one of the “fouling” organisms on the nets included hydrozoans. These are very closely related to jellyfish and have stinging cells known as nematocysts. The pressure cleaning is suspected to have pulverised the hydrozoans, showering the fish with the stingers. Ever since this event, the management has decided not to take short cuts with cleaning their nets.
So, back to this ornamental aquarium fish case. It is suspected that fishes were exposed to toxins within the nematocysts that were released from the “suicidal” anemone, induced by mechanical stimulation/damage. There is no rescuing severely affected fishes. The only things you can do is to remove your fishes from the dangerous waters. Try to catch the fishes out and house them in separate tank. Alternatively, very large water changes would be needed to dilute the dangerous toxins. Chemical filtration and protein skimming may also help.