Resumen de Contribution to the risk assessment of ciguatera poisoning in europe (the balearic and canary islands and the madeira archipelago)
The new climatic conditions, disturbances in the habitat and the exploitation of natural resources seem to stimulate the growth of harmful algal blooms (HABs). Given that these factors will not diminish in the coming years, the scientific community must make an effort to understand, prevent and mitigate the effects of HABs. One of the concerns raised by HABs is Ciguatera Poisoning (CP), which occurs when humans consume fish or invertebrates that contain ciguatoxins (CTXs). These toxins are produced by benthic dinoflagellates of the Gambierdiscus and Fukuyoa genera and they are bioaccumulated through food webs. Apparently, the frequency and intensity of CP cases is tending to increase the world over. One of the reasons for this is the geographical expansion of the Gambierdiscus and Fukuyoa species.
The general objective of this thesis is to contribute to the risk assessment of CP in two zones in Europe: the West Mediterranean Sea (the Balearic Islands) which is a CP-free zone and the North East Atlantic Ocean (Madeira, Desertas, Selvagens, and the Canary Islands).
To that end, the specific objectives of this thesis are:
In the Balearic and Canary Islands:
• Determine which species within Gambierdiscus and Fukuyoa genera live in the respective archipelagos.
• Determine the geographical distribution and the recurrence in several years of Gambierdiscus and Fukuyoa species.
• Assess if these species can produce compounds with CTX-like and MTX-like activity.
• Characterize their toxic profiles further than CTX and MTX compounds.
• Assess the toxicity of fish caught due to CTX-like compounds.
• Contribute to the assessment of CP risk in the Balearic Islands based on what has been mentioned above.
In the Madeira Archipelago:
• Assess the toxicity of fish by CTX-like compounds that was caught in the Archipelago.
• Examine and compare two methods of toxin extraction for fish.
• Compare results of toxin analysis of flesh and liver extracts from the same fish.
• Characterize the toxic profiles of toxic fish by CTX-like compounds from the Archipelago This thesis has the following structure:
Chapter 1 contains a general introduction which consists of two main parts. The first one includes a brief and general description of the microalgae, harmful microalgal blooms (HABs) and the problems associated with HABs. The second part focuses on Ciguatera Poisoning (CP), and the causative species (geographical distribution, the produced metabolites, and the methods of detection).
Chapter 2 states the main objectives and hypotheses of this thesis.
Chapter 3, results are presented and are subdivided in 3 parts: contribution to the assessment of the risk of CP. 1) in the Balearic Islands, 2) the Canary Islands and 3) the Madeira Archipelago.
In the Balearic and Canary Islands, the risk of CP is assessed through the presence and the geographical distribution of Gambierdiscus and Fukuyoa species and the production of potential ciguatoxins and maitotoxins. For that, Gambierdiscus and Fukuyoa cells from the Balearic and Canary Islands were isolated, cultured and identified at the species level by molecular methods. The evaluation of the production of ciguatoxins and maitotoxins was performed using neuroblastoma cell-based assay (neuro-2a CBA), the erythrocyte lysis assay (ELA), immunoassays, and analytical methods. This chapter also includes unpublished results of toxicity of fish from the Balearic Islands using neuro-2a CBA. In the Madeira Archipelago, the risk of CP is based on the detection of ciguatoxins in fish. To that, the toxicity of fish was screening using the neuroblastoma cell-based assay; afterwards, the confirmation of toxins was performed by analytical methods.
Chapter 4 includes the general discussion.
Chapter 5 states the conclusions of this thesis and provides future perspectives about this research.
The findings achieved in this thesis lead to draw the following conclusions:
In the Balearic Islands:
• The genus Gambierdiscus is present in the islands and is described for the first time in the Western Mediterranean Sea.
• Populations of G. australes and F. paulensis in the Balearic Islands are widespread in the different islands and have been recurrent for several years, from 2016 to 2020, indicating that their presence is not circumstantial and that these populations are well established. • G. australes and F. paulensis strains isolated from samples from the Balearic Islands exhibited moderate and low levels of CTX-like toxicity. Moreover, the production of CTX-compounds was confirmed by immunological detection.
• No CTX-like toxicity was obtained in the 36 fish caught from the Balearic Islands, either in the flesh or the liver.
• At present, we estimate that CP risk in the Balearic Islands exists but is low, considering the persistent and wide distribution of Gambierdiscus and Fukuyoa populations having low CTX-like toxicity, and the lack of toxicity in fish.
In the Canary Islands: • The Fukuyoa genus is not present in the Canary Islands.
• G. belizeanus has been reported for the first time in the Canary Islands, raising from six to seven the number of Gambierdiscus species present.
• G. belizeanus produce CTX-like compounds but exhibited low CTX-like toxicity, Therefore, its contribution to CP is low.
• Considering the highest CTX-like and MTX-like toxicity levels, the species that contribute most to CP are G. excentricus and G. australes.
In Madeira Archipelago:
• Fish species of families Kyphosidae, Serranidae, Muraenidae, Labridae, Balistidae and Scaridae presented CTX-like toxicity.
• Kyphosus sectatrix (bermuda sea chup, fam. Kyphosidae) is described as a CTX-like containing species in the Atlantic Ocean for the first time.
• Among the species evaluated, moray eels were the most toxic according to CTX-like toxicity.
• The extraction protocol for CTXs in fish based on Yogi et al. 2011 is more efficient than the protocol of Lewis et al. 2003 based both on the presence of CTX-like toxicity.
• Levels of CTX-like toxicity were higher in the liver than in the flesh of fish. Therefore, detection of CTX-compounds in the liver of fish can contribute to describe the transfer and biotransformation of CTXs in the food webs in a specific area.
• The estimated levels of CTXs were higher than the safety recommendations for EFSA and FDA both in flesh or liver.
• The finding of a new CTX analogue shows that there is still a lack of knowledge of which compounds can contribute to CP.
