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Frequently Asked Questions About Toxic Shellfish Events

Are the shellfish for sale in shops safe to eat?

Yes - all the commercial shellfish growing areas have in place a strict monitoring programme for shellfish toxins. For more information see the "Marine Biotoxin Status for Commercial Shellfish Growing Areas in New Zealand" page.

How quickly can toxin levels change?

Toxicity in shellfish can change quickly - sometimes overnight so you may have got away with eating shellfish from a site one day and not do so a few days later. The area affected by closure is determined by the nearest point at which toxins were either absent, or at levels below the closure level. Areas adjacent to closed areas are usually monitored more intensively in case a bloom spreads.

How variable are the toxins within a shellfish species?

Overseas studies have shown that shellfish from the same area can have very different toxin levels. Some neighbouring shellfish have been found to vary by over 30 times. It is not possible to tell from looking at the shellfish which is toxic and which is not. This may be because blooms can be very "patchy" and may be found at specific depths in the water. It is also not possible to say how quickly levels of toxins can change in shellfish from any given site. What was safe to eat last week may be a very different proposition this week.

Do the toxins affect the flesh of fish?

The NZFSA advises people that it is safe to eat the muscle of fish, but not the guts of fish that feed on algae or shellfish. The gut contents of these fish should be disposed of carefully, so that animals like cats and dogs cannot feed on them. There have been reports of cats and dogs becoming seriously ill from eating toxic shellfish, and possibly the guts of fish. Cooking does not destroy the toxin and can spread it from the gut to other parts of the fish so it is important to gut species that may feed on shellfish or plankton before cooking.

Are marine species other than shellfish affected?

Crabs that feed on shellfish may accumulate toxins in the area (hepatopancreas) under the top shell (carapace) of the crab. We therefore advise the public that this area of the crab should not be eaten until we can review its safety. Crabs and crayfish should be gutted prior to cooking as cooking the animal whole may spread the toxins from the gut to the flesh.

How are the shellfish monitored?

The NZFSA manages a monitoring programme that regularly tests shellfish for toxins and seawater for toxic algae around the main recreational shellfish harvesting areas in New Zealand.

During a bloom, extra monitoring is carried out, firstly to track the progress and spread of the bloom and secondly to study what is happening with the particular event and its effect on the toxicity of different kinds of shellfish.