Parasite found in Mahurangi mullet

The Ministry for Primary Industries has confirmed that a number of Yellow Eyed Mullet (Aldrichetta forsteri) are infected with the myxozoan parasite Myxobolus episquamalis. These fish are located in the Mahurangi River in Warkworth, Auckland.

Myxobolus episquamalis has been previously found in grey mullet (Mugil cephalus) in New Zealand in 2013, from the same region. However, this appears to be the first confirmed case in YEM.

YEM and grey mullet have overlapping populations, so M. episquamalis may have been present in YEM since 2013. 

Myxobolus episquamalis cause granular lesions across the surfaces of the body, which may lead to secondary bacterial infection, but has not been associated directly with mortalities.

The factors that contribute to the increased prevalence of M. episquamalis in affected populations are unknown. Possibilities include changes due to the parasite’s secondary host life-cycle or increased host stress in YEM due to spawning or environmental factors.

YEM and grey mullet are popular fish, often used for bait, and a commercial species. Using affected fish as bait can spread this disease.

There is some evidence in literature that Myxobolus sp. can make people unwell if affected fish are ingested. Additionally, affected fish are susceptible to secondary bacterial infections that can affect people (e.g. Vibrio, Flavobacterium).

We advise people do not consume fish with lesions and wash their hands thoroughly if they have come into contact with them.

Affected fish are highly visible and lesions may be of concern to members of the public.

The notifier has also indicated that affected fish may have been seen in a different river system further north. No follow up information has been provided yet.

Biosecurity NZ has encouraged the notifier to continue to submit reports on this issue and will continue to monitor further notifications from the area to gain further information about prevalence and distribution. They have also been asked to pass this message on within their community.