By Gio Braidotti
Few people in Australia had ever heard of scombroid fish poisoning prior to the tragic death of Queenslander Noelene Bischoff, 54, and her daughter Yvana, 14, while holidaying in Bali, Indonesia, in January 2014.
Public surprise over the deaths – along with the difficulty initially identifying the cause of death – is understandable in retrospect. Scombroid poisoning is rare; however, the chances can be almost eliminated entirely with good cooling and refrigeration of fish catches.
More typically, scombroid poisoning causes symptoms that resemble an allergic reaction, including skin flushing, a throbbing headache, oral burning, abdominal cramps, nausea, diarrhoea and palpitations. Symptoms usually occur within 10 to 30 minutes of eating affected fish.
Australian food safety researcher Alison Turnbull says she too was initially perplexed by the reported deaths, despite chairing SafeFish. SafeFish is a partnership of seafood stakeholders (including funding agencies the FRDC and the Australian Seafood Cooperative Research Centre), regulators and researchers that advise on food safety and hygiene issues, particularly their effects on Australian seafood trade and marketing.
Based at the South Australian Research and Development Institute, where she is leader of the seafood sub-program, Food Safety and Innovation, Alison Turnbull explains that there are two basic types of agents that cause fish poisoning but it is extremely rare for either to cause sudden death.
The first type are biological agents such as bacteria, parasites and viruses that are present in a fish’s growing area or contaminate the fish during processing and packaging. These are well controlled in Australia.
The second type are chemical agents. This category includes heavy metals such as methylmercury (which can cause developmental problems if present in high levels) and cadmium (a carcinogen) for which there are industry standards in place in Australia.
This category also includes harder to detect ‘biotoxins’ that are made by marine algal microorganisms and then accumulate within marine food chains and ultimately can poison humans.
Scombroid straddles the biological and chemical categories since poisoning is due to a chemical (histamine), the post-catch production of which is dependent on enzymes produced by the concurrent overgrowth of fish bacteria.
The key is preventing the bacterial overgrowth. This can be done through proper post-catch handling, in particular cooling and refrigerating caught fish. These two factors are important in preventing poisoning.
Of all the potential causes of food poisoning, the most common in Australia are due to the ciguatoxins found in warm-water finfish from both commercial and recreational catch.
Alison Turnbull explains that the ciguatoxin precursor compounds are produced by algae that grow in warm tropical reef areas, often as a result of ecological and/or climatic disruptions.
However, she says the geographical range of these organisms appears to be expanding (possibly associated with climate change) as the algae were recently found off the coast of southern New South Wales.
Not all fish accumulate ciguatoxins in their fat deposits but when they do, it is generally older (therefore bigger) specimens that cause problems for human health.
Recommendations about which species and sizes to avoid consuming are available to consumers (see page 39), but a simple golden rule is to avoid overly large predatory reef fish.
OzFoodNet data from 2001–10 shows there have been a total of 283 ciguatoxin poisonings in Australia during that decade (compared with 94 cases of scombroid poisoning).
Recent occurrences include cases in northern Queensland and the Gold Coast, with many poisonings resulting from the consumption of Spanish Mackerel (Scomberomorus commerson).
“There is a rule of thumb that you shouldn’t be eating Spanish Mackerel heavier than 10 kilograms,” Alison Turnbull says.
“That is a management strategy developed by Sydney Fish Market and most fish wholesalers will be aware of these recommendations but the message also needs to spread to recreational fishers.”
The problem with ciguatoxins is their high toxicity, which results in debilitating illness (ciguatera) of unpredictable duration. Most commonly poisoning causes gastrointestinal symptoms (nausea, vomiting and diarrhoea) and neurological effects (headache, tingling and numbness, dizziness, extreme itchiness and hallucinations) or, in more severe poisonings, cold allodynia in which the perception of hot and cold are reversed.
Symptoms resolve over a few days, weeks or months but in extreme cases (or perhaps in a subset of especially susceptible people), a chronic multi-symptom illness can develop that lasts for years.
Currently, there is neither a treatment for ciguatera nor a simple diagnostic test for ciguatoxins, although one is needed since these biotoxins do not affect the appearance, odour or taste of fish and are not destroyed by cooking.
Furthermore, once ciguatoxin-exposed people have recovered they are likely to experience worse symptoms if they consume the toxin again.
“There is a lot of work going on around the world to develop a commercial ciguatoxin test, particularly a screening method that can be used to test fish catches before they reach the market,” Alison Turnbull says.
“However, knowing which species and sizes to avoid consuming is an effective food safety strategy and fish you buy from a retailer is safe to eat. It is equally important for recreational fishers who keep their catch to be aware of the species and sizes.
“It is important to realise that poisonings are rare, whereas consuming seafood confers many benefits: it is an important source of protein and nutrients such as iodine, selenium, vitamins A and D, and omega-3 fatty acids.”
Generally, there are geographical ‘hot spots’ for ciguatera around the world, including coastal and oceanic waters off Queensland and the Northern Territory.
However, recreational fishers need to be aware that in February 2014 the NSW Food Authority reported four ciguatera food poisonings resulting from the consumption of a large Spanish Mackerel caught by a licensed fisher on Chaos Reef, south-east of Evans Head, NSW.
Internationally, the high-risk areas generally occur around the tropical band – the South Pacific, Hawaii, the Caribbean and the Gulf of Mexico.
Although biotoxins are also a potential problem in shellfish, the Australian Shellfish Quality Assurance Program has been effective in preventing illness. There are four major groups of shellfish biotoxins, three of which are present in Australian fisheries but actively managed. These are the paralytic, diarrhoeic and amnesic shellfish toxins.
Overall, Alison Turnbull says very few people become ill in Australia from fish poisoning. “Generally, fish poisoning tends to be more of a hazard in developing countries that do not have any management in place and where there is a large percentage of the population subsisting on recreational fishing,” she says.
Adding to consumer protection is the establishment two years ago of a centralised laboratory in Sydney to detect marine biotoxins (other than ciguatoxins) using advanced chemical analysis technology. Prior to this testing was done by mouse bioassays.
“With all these issues, consumers need to be aware that there isn’t just a risk associated with eating seafood – there are also important health and nutritional benefits to seafood, especially to the cardiovascular and immune systems,” she says.
“That is why Food Standards Australia New Zealand analyses both the risks and benefits when deriving its recommended national dietary guidelines that currently recommend two to three serves of fish a week for adults other than pregnant women (or one serve of shark or billfish).”
A summary of hazards in seafood can beviewed here
Sydney Fish Market will not sell any of the following species:
||All warm water ocean fish|
The following Queensland waters:
All warm water ocean fish
||All warm water ocean fish|
The following Northern Territory waters:
The following species
||Coral Trout (Plectropomus spp.)|
||Size limit (kilograms)
|Pickhandle Barracuda (Sphyraena jello)
|Coral Rockcod (Cephalopholis miniata)||N/A||3||N/A||N/A||3|
|Coral Trout (Plectropomus spp.)||6||6||6||6||Reject|
|Kingfish (Seriola spp.)||N/A||10||N/A||N/A||10|
|Mackerel [various] (Scomberomorus spp.)||10 (whole) or 8 (for headed and gutted fish||N/A||N/A||10|
|Giant Queenfish (Scomberoides commersonnianus)||N/A||10||N/A||N/A||10|
|Red Emperor (Lutjanus sebae)||N/A||6||N/A||N/A||6|
|Lined Bristletooth [also known as Surgeon Fish] (Ctenochaetus striatus)
|Spangled Emperor (Lethrinus nebulosus)
|Spanish Mackerel (Scomberomrous commerson)
||10 (whole) or 8 (for headed and gutted fish||N/A||N/A||10|
|Trevally (Caranx spp.)||N/A||6||N/A||N/A||6|
|Tuskfish (Choerodon spp.)||N/A||6||N/A||N/A||6|
Source: Sydney Fish Market pty ltd
FRDC Research Codes: 2009-752.10, 2013-054, 2013-234
Alison Turnbull, firstname.lastname@example.org