Fish and Sea Foods Questions and Answers

Q: The organisms driving spoilage of a particular food are collectively called

Correct answer: the specific spoilage organismsOnly a small fraction of the flora present on a food actually causes its spoilage, and those are the specific spoilage organisms. The distinction matters practically: shelf life correlates with the growth of that subset, not with the total viable count, which may be dominated by organisms doing nothing at all.

Q: Which genera predominate among the specific spoilage organisms of fish?

Correct answer: Pseudomonas, Shewanella and AeromonasThese are Gram-negative, psychrotrophic and aerobic, which is precisely the combination suited to chilled fish stored in air. They grow well at ice temperature and produce the volatile compounds responsible for the characteristic off odours, so they set the shelf life of iced fish.

Q: Trimethylamine oxide in fish serves spoilage bacteria as

Correct answer: a terminal electron acceptorMarine fish carry trimethylamine oxide as an osmolyte, and spoilage bacteria such as Shewanella respire on it when oxygen runs short, reducing it to trimethylamine. That is why marine fish develop the characteristic fishy ammoniacal smell and freshwater fish, which contain far less of the oxide, do not.

Q: Which compound is regarded as an excellent indicator of fish spoilage?

Correct answer: TrimethylamineTrimethylamine is the reduced product of the fish’s own trimethylamine oxide and is essentially absent from fresh fish, so its concentration rises directly with the activity of the spoilage flora. It is easily measured, it is what the nose detects, and it correlates well with sensory rejection.

Q: Which organism is described as a main destructive agent of marine fish at low temperature?

Correct answer: Shewanella putrefaciensShewanella putrefaciens is psychrotrophic, reduces trimethylamine oxide and produces hydrogen sulphide, making it the dominant spoiler of iced marine fish stored aerobically. The species name records exactly what it does.

The organisms driving spoilage of a particular food are collectively called

A.the specific spoilage organisms
B.the general indicator organisms
C.the added starter culture
D.the total viable count

Answer: A

Correct answer: the specific spoilage organisms

Only a small fraction of the flora present on a food actually causes its spoilage, and those are the specific spoilage organisms. The distinction matters practically: shelf life correlates with the growth of that subset, not with the total viable count, which may be dominated by organisms doing nothing at all.

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Which genera predominate among the specific spoilage organisms of fish?

A.Saccharomyces, Candida and Aspergillus
B.Pseudomonas, Shewanella and Aeromonas
C.Lactobacillus, Streptococcus and Bacillus
D.Salmonella, Shigella and Escherichia

Answer: B

Correct answer: Pseudomonas, Shewanella and Aeromonas

These are Gram-negative, psychrotrophic and aerobic, which is precisely the combination suited to chilled fish stored in air. They grow well at ice temperature and produce the volatile compounds responsible for the characteristic off odours, so they set the shelf life of iced fish.

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Trimethylamine oxide in fish serves spoilage bacteria as

A.a source of dietary calcium
B.an inhibitor of growth
C.a terminal electron acceptor
D.a sole source of carbon

Answer: C

Correct answer: a terminal electron acceptor

Marine fish carry trimethylamine oxide as an osmolyte, and spoilage bacteria such as Shewanella respire on it when oxygen runs short, reducing it to trimethylamine. That is why marine fish develop the characteristic fishy ammoniacal smell and freshwater fish, which contain far less of the oxide, do not.

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Reduction of trimethylamine oxide by bacteria produces

A.hydrogen peroxide
B.lactic acid
C.ethanol
D.trimethylamine

Answer: D

TMAO is reduced to trimethylamine, and TMA is responsible for the characteristic fishy odour of spoiling fish. Its accumulation is used as an indicator of spoilage, because it tracks bacterial activity closely and is straightforward to measure.

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Which compound is regarded as an excellent indicator of fish spoilage?

A.Trimethylamine
B.Glucose
C.Lactose
D.Ascorbic acid

Answer: A

Correct answer: Trimethylamine

Trimethylamine is the reduced product of the fish’s own trimethylamine oxide and is essentially absent from fresh fish, so its concentration rises directly with the activity of the spoilage flora. It is easily measured, it is what the nose detects, and it correlates well with sensory rejection.

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Which organism is described as a main destructive agent of marine fish at low temperature?

A.Aspergillus niger
B.Shewanella putrefaciens
C.Bacillus subtilis
D.Lactobacillus plantarum

Answer: B

Correct answer: Shewanella putrefaciens

Shewanella putrefaciens is psychrotrophic, reduces trimethylamine oxide and produces hydrogen sulphide, making it the dominant spoiler of iced marine fish stored aerobically. The species name records exactly what it does.

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Hydrogen sulfide in spoiling fish arises from bacterial metabolism of

A.starch stored in the muscle
B.oil held in the tissue
C.sulfur-containing amino acids
D.trimethylamine oxide alone

Answer: C

Shewanella putrefaciens degrades sulfur-containing amino acids and proteins to hydrogen sulfide, which is considered a main source of fishy odour alongside trimethylamine. The two products together account for most of what the nose detects in spoiled fish.

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Several days after capture, which genus dominates TMAO reduction in fish from cold water?

A.Pseudomonas
B.Lactobacillus
C.Clostridium
D.Shewanella

Answer: D

The dominant reducer depends on where the fish came from: Shewanella in cold-water fish and pseudomonads in warm-water fish. Either way the reaction produces trimethylamine, so the spoilage endpoint looks the same even though the flora differs.

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In a warm-water species held for several days, the leading reducer of TMAO would be a member of

A.the pseudomonads
B.the shewanellae
C.the photobacteria
D.the aeromonads

Answer: A

Pseudomonads take the leading role in warm-water fish, where Shewanella dominates in cold-water fish. The product, trimethylamine, is the same in both cases, so the odour of spoilage does not reveal which genus was responsible for producing it.

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10.

Which organism reduces TMAO in vacuum-packed fish along with Shewanella?

A.Bacillus cereus
B.Photobacterium phosphoreum
C.Staphylococcus aureus
D.Listeria monocytogenes

Answer: B

Photobacterium phosphoreum and members of the Vibrionaceae join Shewanella putrefaciens in using TMAO as an electron acceptor once oxygen has been excluded from the pack. Removing oxygen therefore changes which organisms spoil the fish rather than preventing spoilage.

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