Penis-eating fish introduced into New Zealand

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An unusual species of fish from Australia is preying on penises in New Zealand.

The Australian oyster blenny, Omobranchus anolius, which is believed to have been introduced into New Zealand from Australia (see distribution map), is reportedly preying on local barnacles and eating their penises.

Student Jeremy Barker is researching the species in an attempt to determine how far it has spread.

Barker told Stuff.co.nz: "We have found a large number of penises inside their stomachs. It's not killing the barnacles but it will stop the next generation being produced.""We have found a large number of penises inside their stomachs..."

Dead oysters

The blenny, which often lives inside the shells of dead oysters, is most commonly found in the water in or under submerged objects such as large boulders at low tide.

Around half of all specimens found are present inside the shells of dead Crassostrea gigas oysters, or live among colonies of oysters and the calcareous polychaete tubeworms.

The species was first officially recorded from east Auckland in 2004 and identified using taxonomic and molecular characters.

The study, which revealed specimens ranging from small juveniles to large mature males (around 7cm long), concluded that the Australian oyster blenny is either breeding in New Zealand, or has managed to find its way there several times.

Australian oyster blennies are capable of surviving in small quantities of water and experts believe that the species might have been introduced to New Zealand with oysters or oyster shells.

Eradication or control

However, the study said that if eradication or control of the species was considered desirable, the chances of success would be higher than they would be for most other introduced species.

"The intertidal habitat makes the fish accessible at low tide. However, we cannot rule out the possibility that some individuals occur subtidally, and further work is required to determine this."Rarely, individuals enter small crevices or tubes and become trapped as they grow...""Oyster blennies do not flee when found, and have been reported to move by pushing backwards with the pectoral fins rather than swimming forwards.

"Rarely, individuals enter small crevices or tubes and become trapped as they grow, their bodies changing shape to match that of their cell.

"Apparently, O. anolius are not very active or mobile, and they probably do not disperse naturally as adults: movements may only be of the order of metres or perhaps tens of metres.

"Furthermore, larvae are released at a large size, and they too may have limited dispersal."

Unlike the eggs of many other marine fishes, those of the Australian oyster blenny are adhesive and therefore aren't released into the plankton to be dispersed.

For more information see the paper: Francis MP, Walsh C, Smith PJ and MF Gomon (2004) - First records of the Australian blenny, Omobranchus anolius, from New Zealand. New Zealand Journal of Marine and Freshwater Research, vol 38: 671-679.