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Poisonous animals
 
Cnidarians (Jellyfish, Corals and Anemones)
 
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Genus/Species

 

Scombrotoxic fish (Mackerels, Tunas and others)

Clinical entries

Species

Poisoning can be caused by members of the following families (possibly also by others):

 

  1. Scombridae (genera Auxis, Euthynnus, Katsuwonus, Sarda, Scomber, Scomberomorus, Thunnus)
  2. Scomberesocidae (genera Cololabis, Scomberesox)
  3. Carangidae (genera Trachurus, Seriola)
  4. Clupeidae (genera Clupea, Sardinops, Sardina)
  5. Coryphaenidae (genus Corayphaena)
  6. Engraulidae(genera Engraulis, Cetengraulis)
  7. Pomatomidae (genus Pomatomus)
  8. Xiphiidae (genera Xiphias, Makaira)

Taxonomy

Pisces; Osteichthyes

Common names

  1.  Mackerels, Tunas, Bonitos, Skipjacks, Albacore. Makrelen, Thunfische, Bonitos
  2. Sauries, Makrelenhechte
  3. Jacks, Scads, Pompanos, Stachelmakrelen
  4. Herrings, Sardines, Heringe, Sardinen
  5. Dolphinfish, Goldmakrelen 
  6. Anchovies, Sardellen 
  7. Bluefish, Blaubarsch
  8. Swordfish, Marlins, Schwertfische, Marline

Distribution

The distribution range of potentially scombrotoxic fish extends from tropical to cold seas and oceans. Poisoning can also occur in inland countries through the importation of fish.

 

 

Fig. 4.7  Thunnus thynnus

Biology

Unlike many other poisonous animals, the toxic substances in scombrotoxic fish do not accumulate via the food chain. They occur in the form of histamine and other products of decomposition via putrefactive processes in dead animals. Originally a phenomenon that was primarily observed in the mackerel and tuna families (Scombridae, thus scombrotoxic), there are also several other types of fish that have been associated with scombrotoxism. It is thus appropriate to speak of "scombroid poisoning". Primarily involved are fast-swimming fish that cover great distances, are found in open water and have dark muscle tissue. This tissue is rich in the amino acid histidine. Under natural conditions, histidine is converted to histamine via decarboxylase enzymes from bacteria that are commonly found in the surface flora of fish (Clostridium sp., Klebsiella sp., Proteus sp., Vibrio sp., among others). Optimal growth conditions for such bacteria are in the temperature range 37–43°. However, decarboxylation can already occur at 20–30°. It is thus important that the fish are adequately refrigerated between being caught and consumed. 

Histamine alone is not generally toxic when ingested orally, as it is broken down by diamine oxidase (DAO) in the gastrointestinal tract. Thus, in cases of poisoning due to scombrotoxic fish, there must be accompanying factors that facilitate the absorption of histamine into the blood circulation. It has been argued that putrescine and cadaverine, which are also produced by the decomposition process, compete for DAO and thus facilitate the absorption of histamine. It seems however that various other DAO-inhibitors like tryptamine, thiamine, dipeptides anserine and carnosine found in the fish could play a role along with other inhibitors wich haven't been detected until now.

Risk

After ciguatera, scombrotoxism is by far the most common form of fish poisoning. The estimated number of unreported cases is high, as many cases are not recognised as scombrotoxism, or the poisoning is mild and a doctor is not consulted. There have been no known fatalities to date.

In the United Staes Scombroid poisoning accounts for about 5% of food-borne poisonings and even for 38% of all seafood associated outbreaks. Especially in Hawai Scombrotoxism is a common cause for seafood poisoning and the risk seems to be highest after ingestion of recreational catches. In other countries with high outbreak rates like Denmark, France, Finland or NewZealand  the numbers range from 2 to 5 outbreaks/year/million people.

The consumption of freshly caught fish or fish that have been continuously refrigerated (at <5°C) after being caught is without risk. During storage or transport at higher temperatures, the decomposition process commences and the toxins that then develop cannot be destroyed by frying, boiling or smoking the fish. It is not possible to identify poisonous fish from external characteristics, but those that are of doubtful freshness or have a hot, pepper-like aftertaste should definitely be avoided.

Preserved fish such as tuna, sardines or anchovies as well as smoked mackerels can also cause poisoning.

The histamine content can vary greatly within the same fish. In the USA, the Food and Drug Administration (FDA) has set the critical limit in tuna at 50 mg/100 g. However, signs of poisoning can already occur with a concentration of 20 mg/100 g and less. In refrigerated and frozen animals the histamine content is generally under 5 mg/100 g.

The most common causes of scombrotoxism are members of the Scombridae and Scomberesocidae families. One of the reasons for this is that tuna and mackerels are very commonly eaten throughout the world. However, other non-scombroid fish may also be of high epidemiological relevance in certain areas. Thus in the USA between 1973 and 1986, 178 outbreaks were reported with 1,096 people involved. Most of the cases of poisoning in these outbreaks were traced to Coryphaena hippurus (Mahi mahi), followed by tuna and the Bluefish Pomatomus saltatrix (MMWR 1989). According to a study in England, the most significant cause of poisoning there after mackerels and tuna are sardines (Bartholomew et al. 1987).

Some of the families named here can also cause ciguatera poisoning (Table 4.1).

Literature (biological)

Taylor et al. 1989, MMWR 1989, Etkind et al.1987, Murray et al. 1982, Bartholomew et al. 1987, Halstead 2001a, Hungerford 2010