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New record of an introduced parasite in Southern Waters

28 October 2016
FOR IMMEDIATE RELEASE

Discovery of a new fish parasite in the South Island thankfully poses no risk to humans and overseas research indicates there will be minimal impact on the fishery.

Doctor Clement Lagrue from the University of Otago has led the efforts to identify the parasite after an angler contacted the Ecological Parasitology Laboratory at the University of Otago following their discovery in a fish they caught in Lake Hawea (see pictures below).

Morphological and genetic analyses conducted at Otago, and particularly by Doctor Bronwen Presswell, have confirmed the identity of this parasite as Ligula intestinalis, a large cestode introduced from the Northern Hemisphere.

Before going into details about the little critter, be assured that this parasite if of no health concern and does not pose a risk to human health.

Fish infected with the parasite can safely be eaten and anglers should have no apprehension about consuming their catch or even about any change of taste.

Ligula intestinalis has what is called a complex life cycle where the parasite needs three different host species to complete a generation; fish are actually only part of the parasite development and not the end point.

Adult parasites live in the guts of fish eating birds, most likely Crested Grebes and shags in New Zealand central lakes, and the eggs are released in the water with the bird feces. The life cycle of the parasite then goes as shown below.

Although this parasite was anecdotally recorded from New Zealand previously, it had never been documented from the South Island.

It was thought to have been introduced occasionally to the North Island by infected birds (the definitive hosts) travelling from Australia where Ligula intestinalis is also present, and appeared not to persist for long in New Zealand waters.

However, these new records show that it is indeed present and that a variety of fish from Lake Hawea serve as hosts to the parasite.

Although the parasite is unlikely to significantly affect fish populations as a whole, and thus salmonid fisheries, it can have fairly severe pathological effects on its individual fish host when numbers get high.

Effects include reduced body condition and fecundity, tissue inflammation (see picture of the salmon above) and mortality.

Before drawing any conclusion on the distribution and potential effects of this new parasite in South Island lakes, we need to gather information as quickly as possible and that’s where anglers can help.

If you catch salmonids from central lakes, please check for the presence of the parasite and if you do find it record the location of the catch, fish species, number of individual parasites in the fish and total fish weight and length.

Please report this to: clement.lagrue@otago.ac.nz or Otago Fish and Game: otago@fish-game.org.nz.

Once enough information is gathered and we have a clearer picture of the situation, information will be transmitted back to Fish and Game, and then to anglers.

Members of the Otago Parasitology team will also be present at the Lake Hawea fishing competition in November to collect samples and provide information to interested parties.

Collaboration from anglers at this time will be much appreciated. Once again, information gathered then will be shared with anglers once results have been analysed.

ENDS

WHAT IS FISH & GAME?

Fish & Game is a statutory public entity, established by Parliament under the Conservation Act, to manage, maintain and enhance sports fish and gamebirds, and their habitats. It is not a lobby group but an organisation with specific responsibilities under Acts of Parliament, including the Conservation, Resource Management, Walking Access, Public Finance and Overseas Investment Acts.

The New Zealand Fish & Game Council represents the interests of anglers and gamebird hunters nationally. The Council and the 12 regional Fish & Game councils are collectively known as Fish & Game New Zealand. Fish & Game receives no money from the government. All funding is provided by freshwater anglers and gamebird hunters – a “user pays, user says” tradition dating back 150 years.

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