Fish and Sea Foods Questions and Answers

Q: Fish families implicated in histamine poisoning are characterised by a high content of

Correct answer: free histidineScombroid poisoning is confined to fish with a naturally high free histidine content - tuna, mackerel, bonito, sardine, mahi-mahi and their relatives. Without the substrate the bacteria cannot make the toxin, which is why cod and other white fish are not implicated however badly they are handled.

Q: Which symptom is typical of histamine poisoning?

Correct answer: Flushing and headacheThe symptoms are those of an allergic reaction because histamine is the mediator of one: flushing, headache, palpitations, sweating, an urticarial rash, sometimes a peppery taste in the mouth. Onset is within minutes to an hour and recovery is usually within a day, which distinguishes it from a bacterial infection.

Q: The European maximum limit for histamine in fresh fish is

Correct answer: 200 mg/kgThe European criterion sets a mean of 100 mg/kg with no sample above 200 mg/kg for fish species associated with a high histidine content. The limits are set well below the levels that cause symptoms, so exceeding them indicates a control failure rather than an immediate hazard.

Q: The practical control against histamine formation is

Correct answer: rapid chilling and temperature controlSince the toxin survives every subsequent process, the only effective measure is preventing its formation - chilling the fish on capture and holding the chain unbroken to the consumer. Cooking, washing and later freezing are all useless once the histamine is present.

Q: Vibrio bacteria naturally live in

Correct answer: coastal salt and brackish waterVibrio species are part of the natural marine flora, particularly in warm coastal and estuarine water, and their presence indicates nothing about sewage contamination. This is why they cannot be eliminated at source and why shellfish harvesting controls concentrate on temperature and on treatment after harvest.

Q: Which Vibrio species causes the most severe and life-threatening infections?

Correct answer: Vibrio vulnificusV. vulnificus causes septicaemia rather than a self-limiting gastroenteritis, invading the bloodstream from the gut or through a wound exposed to seawater. It is far less common than V. parahaemolyticus but vastly more dangerous, and it is the reason raw oysters carry warnings for at-risk groups.

Q: Approximately what proportion of people infected with Vibrio vulnificus die?

Correct answer: About one in fiveThe case fatality rate for V. vulnificus septicaemia is around twenty per cent, and higher still in those with liver disease. Death can follow within a day or two of onset, so treatment depends on recognising the infection early in someone who has recently eaten raw shellfish.

21.

Fish families implicated in histamine poisoning are characterised by a high content of

A.free histidine
B.trimethylamine oxide
C.fat
D.calcium

Answer: A

Correct answer: free histidine

Scombroid poisoning is confined to fish with a naturally high free histidine content - tuna, mackerel, bonito, sardine, mahi-mahi and their relatives. Without the substrate the bacteria cannot make the toxin, which is why cod and other white fish are not implicated however badly they are handled.

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22.

Which symptom is typical of histamine poisoning?

A.Loss of hearing
B.Flushing and headache
C.Paralysis of the limbs
D.Jaundice lasting weeks

Answer: B

Correct answer: Flushing and headache

The symptoms are those of an allergic reaction because histamine is the mediator of one: flushing, headache, palpitations, sweating, an urticarial rash, sometimes a peppery taste in the mouth. Onset is within minutes to an hour and recovery is usually within a day, which distinguishes it from a bacterial infection.

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23.

The European maximum limit for histamine in fresh fish is

A.2000 mg/kg
B.5 mg/kg
C.200 mg/kg
D.20 mg/kg

Answer: C

Correct answer: 200 mg/kg

The European criterion sets a mean of 100 mg/kg with no sample above 200 mg/kg for fish species associated with a high histidine content. The limits are set well below the levels that cause symptoms, so exceeding them indicates a control failure rather than an immediate hazard.

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24.

The practical control against histamine formation is

A.cooking thoroughly before sale
B.washing the fish in fresh water
C.freezing after two days held at ambient
D.rapid chilling and temperature control

Answer: D

Correct answer: rapid chilling and temperature control

Since the toxin survives every subsequent process, the only effective measure is preventing its formation - chilling the fish on capture and holding the chain unbroken to the consumer. Cooking, washing and later freezing are all useless once the histamine is present.

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25.

Vibrio bacteria naturally live in

A.coastal salt and brackish water
B.inland freshwater lakes only
C.dry soil well away from the coast
D.the human intestine and nowhere else

Answer: A

Correct answer: coastal salt and brackish water

Vibrio species are part of the natural marine flora, particularly in warm coastal and estuarine water, and their presence indicates nothing about sewage contamination. This is why they cannot be eliminated at source and why shellfish harvesting controls concentrate on temperature and on treatment after harvest.

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26.

Most people acquire vibriosis by eating

A.cold-smoked salmon served in thin slices
B.raw or undercooked shellfish, particularly oysters
C.white fish such as cod, thoroughly cooked through
D.commercially canned tuna packed in brine

Answer: B

Correct answer: raw or undercooked shellfish, particularly oysters

Oysters filter large volumes of water and concentrate whatever is in it, and they are commonly eaten raw and whole - gut included. The combination of concentration and no cooking step is what makes them the dominant vehicle for vibriosis.

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27.

Vibrio are found in higher numbers in coastal water during

A.no particular season
B.only after heavy rain
C.May through October
D.November through February

Answer: C

Numbers rise from May through October, when water temperatures are warmer. The seasonality of the organism is reflected in the seasonality of the illness, since more organisms in the water means more concentrated in the shellfish that filter it.

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28.

Why does vibriosis show a seasonal pattern?

A.Shellfish are only ever harvested during summer
B.People eat fish only during the summer months
C.Colder water increases the number of Vibrio present
D.Vibrio numbers rise as water temperature rises

Answer: D

Correct answer: Vibrio numbers rise as water temperature rises

Vibrio multiply in warm water, so their numbers in coastal water and in the shellfish filtering it rise sharply through the summer. The old advice about months with an R in them reflected this before refrigeration, and warming seas are extending the season and the geographical range.

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29.

Which Vibrio species causes the most severe and life-threatening infections?

A.Vibrio vulnificus
B.Vibrio parahaemolyticus
C.Vibrio alginolyticus
D.Vibrio fischeri

Answer: A

Correct answer: Vibrio vulnificus

V. vulnificus causes septicaemia rather than a self-limiting gastroenteritis, invading the bloodstream from the gut or through a wound exposed to seawater. It is far less common than V. parahaemolyticus but vastly more dangerous, and it is the reason raw oysters carry warnings for at-risk groups.

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30.

Approximately what proportion of people infected with Vibrio vulnificus die?

A.Fewer than one in a hundred
B.About one in five
C.About one in a thousand
D.About half

Answer: B

Correct answer: About one in five

The case fatality rate for V. vulnificus septicaemia is around twenty per cent, and higher still in those with liver disease. Death can follow within a day or two of onset, so treatment depends on recognising the infection early in someone who has recently eaten raw shellfish.

Discuss in Forum

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