About the project

Project summary

Food risks associated with ciguatoxins: monitoring and tracking the toxins and toxin-producing organisms in marine ecosystems (CIGUARISK)

Ciguatera, also known as ciguatera fish poisoning (CFP), is caused by the ingestion of marine fish containing ciguatoxins (CTXs), which are very potent neurotoxins, mainly present in tropical and subtropical areas worldwide. Ciguatera causes general, digestive, cardiac and long-lasting neurological symptoms that may last for months. CTXs are produced by dinoflagellates of the genera Gambierdiscus and Fukuyoa and are transferred and transformed through the food webs reaching consumers.

Gambierdiscus spp. have been described as a widespread and diverse component of the benthic microalgal communities in the Canary Islands (CI). It is unlikely that the genus is a recently introduced taxon in the Canaries but climate change may have promoted higher population densities. Since 2004, cases of ciguatera have appeared in the CI and in Madeira.

By contrast, in the Mediterranean Sea, no convincing evidence of cases of ciguatera exist, even though Gambierdiscus spp. have been reported in Crete, Cyprus and very recently in the Balearic Islands (BI). However, little is known about the diversity, distribution and toxicity of Gambierdiscus and Fukuyoa in the Mediterranean Sea.

These two temperate regions – the BI having Gambierdiscus but no ciguatera, the CI having both – offer a unique opportunity to evaluate the factors that allow a potential risk of ciguatera to become an actual disease and hence to develop risk assessments for ciguatera in an environment evolving as a result of climate change.

The toxins involved are very diverse: c. 20 CTXs analogues are known, with very different toxicological properties. Analysing them is challenging since extraction methods for these toxins may not be equally efficient in different species of fish and different tissues, and the levels of CTXs observed in fish samples are typically very low.

The main objective of CIGUARISK is to make an integrated assessment of ciguatera risk in order to protect the consumer and advise the fish production sector. A basic prerequisite is to determine the spatiotemporal distribution of Gambierdiscus/Fukuyoa species, precisely identify and quantify the CTXs they produce, and define how CTX profiles are transformed during their passage through the food webs. To accomplish this, field sampling and DNA profiling of Gambierdiscus spp. and Fukuyoa spp. will be combined with CTX characterization (identity and toxicity) in the dinoflagellates and various components of food webs to see how CTX accumulate and how their profiles and toxicities change as they are transferred from alga to herbivorous/omnivorous and to carnivorous fish and other marine organisms. Controlled dietary experiments will be performed to examine uptake and conversions of CTXs by fish. All these data will be brought together and an integrated risk assessment model built in order to predict when ciguatera may occur, hence protecting consumers and providing timely advice to the aquaculture and fishing sectors.

SubProject 1 summary

Spatio-temporal dynamics of ciguatoxin-producing microalgae in marine ecosystems and transfer of ciguatoxins through the food web (CIGUATROFIC)

Ciguatera fish poisoning (CFP) is a foodborne disease mainly in the tropics caused by eating fish containing ciguatoxins (CTXs). Benthic dinoflagellates of the genera Gambierdiscus and Fukuyoa produce CTXs, which are then transferred up the food web. In 2004 the first autochthonous outbreak of ciguatera in Europe was reported from the Canary Islands (CI) after consumption of amberjack fish. Until now, five Gambierdiscus species have been reported in the CI. In the Mediterranean, no ciguatera cases have been confirmed, but Gambierdiscus and Fukuyoa species have been found in Cyprus, Crete and the Balearic Islands (BI). The Mediterranean Sea is strongly affected by rising temperatures accompanying climate change, making the region increasingly suitable for tropical species. Hence there is an urgent need to investigate the spatio-temporal distributions of Gambierdiscus and Fukuyoa to define locations where ciguatera is a potential risk and estimate the likely timescale for its appearance, and to understand how CTXs move through the food web. Comparisons between CI and BI are particularly informative about ciguatera risk because CTX-producers are present in both areas but ciguatera currently develops only in CI.

The presence of CTXs in the flesh of upper trophic level fish, particularly one of the most toxic analogues (CTX-1B), is believed to result from consumption of Gambierdiscus cells by herbivorous and omnivorous fish; then, these are preyed upon by carnivorous species. Subproject 1 CIGUATROFIC focuses on where and when CTX-producing dinoflagellates occur, what controls their growth, their CTX profiles, and how these profiles change as CTXs are transferred in the food webs. The spatial distributions of Gambierdiscus/Fukuyoa in BI and CI will be studied and quantified by microscopical counts, and molecular techniques (Sanger sequencing and DNA metabarcoding). Molecular approaches for identification are needed because CTX-producing species vary greatly in toxicity but cannot be reliably identified by morphology. Temporal and depth distributions will also be examined at a few selected sites where CTX species are sufficiently abundant.

The CTXs produced by the dinoflagellates will be characterized and compared with those present in fish and other organisms to determine how CTX composition and toxicity change during their passage through the food webs. Previous studies indicate that CTXs become more oxidized (e.g. to CTX-1B) as they move through the food web and accumulate in fish tissues because of their lipophilic nature. Screening of CTXs will employ cell-based toxicity assays and liquid chromatography coupled to mass spectrometry (LC-MS/MS and LC-HRMS) to confirm the presence and identities of CTX analogues and their amounts. This characterization of the CTXs in different organisms will help to understand the biotransformation and biomagnification of toxins and toxicity in the food web. Bioaccumulation of CTXs is usually evaluated in muscle tissue but we will also evaluate it in other tissues (liver, stomach) to provide a more complete picture. The information from the spatiotemporal studies of dinoflagellates and toxin analyses in marine organisms will then be integrated to develop a predictive model for ciguatera.

SubProject 2 summary

Ciguatoxin in food web: a controlled study of bioaccumulation in fish species (CIGUAFOOD)

Emergent marine toxins are a major problem involving food safety for fishing and aquaculture products in the world. Marked increase of the prevalence of ciguatoxin and other analogue derivatives in fish and ciguatera fish poisoning in humans has been detected in different regions like the Canary Islands, which represents a best lab to address this issue. Different toxins belong this family could be transmitted to the consumer. And these toxins produce a bio-accumulative effect in the food web, but nothing is known about their mechanism of action, how it affects the toxins profiles, and their influence on the toxic activity for each point of this food web.

New strains of Gambierdiscus will be obtained in this subproject from the hotspots described in Gran Canaria, in order to be included in the Spanish Algae Bank (BEA) collection after their morphologic and genetic identification, but also the rate of growth and biomass production improved. This knowledge is necessary to clarify their contribution in the human intoxication outbreaks by these toxins. These isolated strains will be used to deepening in the toxinic profiles found, and that showing the best results will be included in the bioaccumulation study.

In the other way, different organisms could participate as carriers for ciguatera fish poisoning. Possible species acting as ciguatera fish poisoning carriers in the different points of the food web will also be studied in this project, and checked in the same points described above (hotspots), by using algae as main source of food, or mixed with small fish and shellfish, and both groups are able to accumulate ciguatoxin and other toxin derivatives involved, and finally, main fish predators will also be investigated for their responsibility in human ciguatera fish poisoning.

And the effect of bioaccumulation of these toxins in fish will be also studied in this project, by different challenge exposure to the toxins in experimental fish, by feeding with microalgae strains selected during this project and, at the same time, with death fish, previously identified and quantified for a particular amount (ng/g) of ciguatoxin. These assays will better help to know the kinetic of these toxins in fish.