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collected and concentrated through levels of the food chain (e.g., molluscs, crustaceans, and finfish) and ultimately are consumed by humans (Ward and Hart 1996).
Algae, one of the natural parts of the aquatic food chain, are photosynthetic
organisms ranging from single cell to complex multicellular structures. Algae reproduce enough to accumulate on the water surface in the presence of favourable ambient conditions for their reproduction and this disrupts the aquatic balance. This
rapid increase in algae population is called algae bloom and causes the water to turn
into red, green, or brown. As a result of excessive reproduction and toxin production
of some algae species, a condition called harmful algae bloom arises that threaten
human health. In some of the harmful algae reproduction, various poisons are synthesized depending on the type of microalgae that show excessive reproduction.
Although these poisons exhibit different properties in fresh-brackish water and
marine species, they are all temperature resistant compounds and do not degrade at
cooking temperature (He 2015) This means that even well-cooked bivalves might
still present a risk to consumer’s safety. Accumulation of toxic marine algae in raw
or light cooked shellfish has been associated to Paralytic Shellfish Poisoning (PSP),
Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP),
Amnesic Shellfish Poisoning (ASP) and Azaspiracid Poisoning (AZP) occurrences
(Oliveira et al. 2011).
Bivalve molluscs, especially oysters, are consumed raw in most countries, and
many are marketed as live bivalve molluscs. Because it is difficult to preserve live
shellfish outside their natural environment, this also results in the need for rapid
assessment of their sanitary safety. Factors affecting the occurrence and accumulation of toxic algae cannot be controlled, and the prediction of toxic algae has severe
limitations. Therefore, and because there is a very strong need to market shellfish as
a live product, management practices for safe bivalve mollusc production are very
specific. Official control of shellfish safety is mostly conducted on live shellfish, i.e.
through regular, continuous surveillance of shellfish growing areas (Lawrence
et al. 2011).
Digestive gland, mantle, gonad, and gill tissues all retain the toxins although the
levels vary between tissues and between species (FAO 2004). The ability of shellfish
to retain and accumulate toxins varies greatly according to the shellfish species
(Hegaret and Shumway 2009). For example, mussels accumulate more toxin, and
more rapidly, than most of the other bivalve species. They actively feed on toxic
cells and accumulate high levels of toxins because they have nerves insensitive to
PSP toxins. Oysters accumulate low levels of toxins because they are sensitive to
PSP toxins. The accumulation of PSP toxins in bivalves varies according to external
factors such as temperature, microbiota, presence, and concentration of toxic dinoflagellates (Bricelj and Shumway 1998).
5 Shellfish Safety
collected and concentrated through levels of the food chain (e.g., molluscs, crustaceans, and finfish) and ultimately are consumed by humans (Ward and Hart 1996).
Algae, one of the natural parts of the aquatic food chain, are photosynthetic
organisms ranging from single cell to complex multicellular structures. Algae reproduce enough to accumulate on the water surface in the presence of favourable ambient conditions for their reproduction and this disrupts the aquatic balance. This
rapid increase in algae population is called algae bloom and causes the water to turn
into red, green, or brown. As a result of excessive reproduction and toxin production
of some algae species, a condition called harmful algae bloom arises that threaten
human health. In some of the harmful algae reproduction, various poisons are synthesized depending on the type of microalgae that show excessive reproduction.
Although these poisons exhibit different properties in fresh-brackish water and
marine species, they are all temperature resistant compounds and do not degrade at
cooking temperature (He 2015) This means that even well-cooked bivalves might
still present a risk to consumer’s safety. Accumulation of toxic marine algae in raw
or light cooked shellfish has been associated to Paralytic Shellfish Poisoning (PSP),
Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP),
Amnesic Shellfish Poisoning (ASP) and Azaspiracid Poisoning (AZP) occurrences
(Oliveira et al. 2011).
Bivalve molluscs, especially oysters, are consumed raw in most countries, and
many are marketed as live bivalve molluscs. Because it is difficult to preserve live
shellfish outside their natural environment, this also results in the need for rapid
assessment of their sanitary safety. Factors affecting the occurrence and accumulation of toxic algae cannot be controlled, and the prediction of toxic algae has severe
limitations. Therefore, and because there is a very strong need to market shellfish as
a live product, management practices for safe bivalve mollusc production are very
specific. Official control of shellfish safety is mostly conducted on live shellfish, i.e.
through regular, continuous surveillance of shellfish growing areas (Lawrence
et al. 2011).
Digestive gland, mantle, gonad, and gill tissues all retain the toxins although the
levels vary between tissues and between species (FAO 2004). The ability of shellfish
to retain and accumulate toxins varies greatly according to the shellfish species
(Hegaret and Shumway 2009). For example, mussels accumulate more toxin, and
more rapidly, than most of the other bivalve species. They actively feed on toxic
cells and accumulate high levels of toxins because they have nerves insensitive to
PSP toxins. Oysters accumulate low levels of toxins because they are sensitive to
PSP toxins. The accumulation of PSP toxins in bivalves varies according to external
factors such as temperature, microbiota, presence, and concentration of toxic dinoflagellates (Bricelj and Shumway 1998).
5 Shellfish Safety