Warnings anglers should not eat trout caught in catchments below 1080 drop zones tarnishes New Zealand's reputation as an international fly fishing destination, say angling experts.

International angler numbers and trout fishing licence sales could take a hit on the back of research showing trout which eat mice carrying sub-lethal levels of the poison breached 1080 food safety levels.

The trout fishing season opens today and Nelson Marlborough Fish and Game ranger Lawson Davey said with a fair chunk of the region covered by Department of Conservation and TB-Free operations there would be few catchments in Tasman and Marlborough without 1080 drops this year.

"People can go fishing, just don't eat the fish. With the majority of drops planned for October and November, I suggest anglers get out early and make the most of it now."

Preliminary results of the research, commissioned by DOC and undertaken by Cawthron Institute, show trout that ate mice containing the toxin have levels of 1080 exceeding New Zealand Food Safety Authority limits. The result came as a surprise with the risks higher than previous modelling suggested, he said.

"The concern is that in eating a single mouse [containing a sub-lethal does of 1080], it has been shown a trout poses a risk to human health . . . It suggests there is an issue and further work is needed."

In February DOC rejected the Federation of Freshwater Anglers' claims that people should not eat trout or eels because of a risk the poison could be present.

Davey said the research, combined with trout's migratory tendencies and the fact the poison can last in the trout for 18 days, meant anglers should be wary of fishing downstream of 1080 zones.

He said fly fishing tourism was likely to be impacted. "We have already had a call saying the news has gone global. Tourists tend to catch and release but they have come to expect they are fishing in pristine waters - they do not want to be fishing where poison may have been dropped.

"How big the impact will be is something we have to wait and see, but tourist anglers tend to be among the highest spenders in New Zealand."

Davey said while he has not been involved in the 1080 debate the research raised questions about the sub-lethal effect of 1080 on target and non-target species.

Nelson fly fishing guide Tony Entwhistle said the news was not a good look for New Zealand.

"We have sold New Zealand as the pinnacle for trout fishing in the world. We hold this reputation and people's imaginations have been captured by the ability to go back into the wild and fish in a pristine environment."

Murchison fishing guide Peter Carty said he understood people should avoid eating trout from rivers flowing from 1080 drop zones - affecting nearly all of the region's rivers.

International anglers did tend to catch and release, but those who flew into the backcountry for prolonged guided trips often had trout on the menu, he said.

Murchison fly fishing guide Scott Murray said the research raised questions about previous advice that 1080 broke down in water. "Now they are saying don't eat the trout. To the international angler it looks like some sort of circus - it's a massive contradiction."

DOC boss Lou Sanson has played down the risk of eating 1080-laced trout.

"You would have to eat tonnes of trout to be affected," he said. "Overall the risks are very low."

The research involved feeding trout high levels of 1080 in the lab and preliminary results show that trout take up small amounts of 1080 into their flesh which breaks down over a number of days.

The laboratory tests were not peer reviewed and would need to be replicated in the field to establish credibility, he said. DOC was expressing the need for caution but anglers could still go fishing.