Ciguatera Fish Poisoning (CFP) and the examination of the epiphytic nature of Gambierdiscusn toxicus, a dinoflagellate involved in CFP

Ciguatera Fish Poisoning (CFP) is potentially a global health problem; extensive international exchange of frozen fish have resulted in global cases of CFP. The causative poison: Ciguatoxin (CTX) is acquired by humans through the consumption of contaminated seafood (Friedman et al. 2008). The toxin is heat-stable when exposed to conventional cooking temperatures. It is also tasteless and odorless. The absence of prompt clinical testing has stemmed interesting detection methods, which have been used by some tropical Islanders. A quote from “Folk remedies for tropical fish poisoning in the Pacific” by Lobel. 1979, tells of the numerous and some quite humorous antidotes used by the native islanders.

“(1) cooking the fish with a silver object to see if discoloration results, (2) seeing if the fish repels flies or ants, (3) avoiding sliced fish that fails to reflect a rainbow when held to the sun, (4) rubbing one’s gyms with the liver to see if a tingling results, and (5) giving a sample of the questionable fish to a household pet or an elderly relative as a bioassay…”

The toxin CFX originates in the dinoflagellate Gambierdiscus spp (Friedman et al. 2008). These have been found in association with various macroalgae that live within coral reef ecosystems. Herbivorous fish consume these dinoflagellates through grazing, initiating the process of bioaccumulation and biomagnification up through the food web. Parsons et al. 2011, examined the interaction between Gambierdiscus toxicus cells and 24 macroalgal hosts, with the intention to better document and understand the relationship between the toxin producing epiphytic dinoflagellate and potential algal hosts.

24 samples of macroalgae were collected from coastal waters at Leleiwi Park in Hilo, Hawaii. Algal specimens were identified. The samples were cleaned with filtered seawater, removing detritus and epiphytes. 100g (wet weight) of each sample were placed respectively into Petri dishes containing 10ml of Keller’s medium. 0.1 ml aliquots of G. toxicus BIG12 were added to each sample (approximately 100 cells per Petri dish). The Gambierdiscus cells were counted immediately after manipulation and then: two, 16, 24 and every 24-72 hours thereafter. Observations were recorded within classes: ‘alive and attached/in contact with host’, ‘alive but unattached’ and ‘dead’. The experiment was conducted over a 29-day period.

Parson et al. 2011 converted the data classes into relative abundance values; i.e. % of total cells alive and attached. Within the experiment there were cases where counts were missing for some Petri dishes, Parson et al. 2011 state: “the missing points were extrapolated using previous and subsequent days” in the write up it is discussed that this is less than optimal but required so as to allow for subsequent statistical analysis. However, the reasoning as to why there were “missing counts” was very ambiguous! I’m guessing that it’s due to human error when conducting the experiment! This is less than desirable, but the error has been acknowledge and if occurred in, as stated a “few cases”, the effect on the results should be minimal. For all statistical tests PRIMER 6 was used. A Bray-Curtis similarity index was carried out to group/“cluster” together the different algal hosts based on the three parameters: % alive and attached, % alive and unattached and % dead. Similarity profile permutation test (SIMPROF) were used to assess significant differences between “clusters”. These host species could be categorized into 14 significantly different groups. In terms of the epiphytic nature of the Gambierdiscus toxicus, the cells would not attach to the group containing these algal species: Bryopsis sp. and Portieria hornemannii (Group A), but did attach to other species: Dasya sp., Siphonous sp., Acanthophora spicifera, Amansia glomerata, Centroceras sp., Ceramium sp., Chaetomorpha sp., Dudresnaya sp., Jania sp., Tolypiocladia glomerulata and Turbinaria ornate. However, these results obtained differ to a previous study by Grzebyk et al. 1994, in which P. hornemannii was found to stimulate Gambierdiscus growth, not inhibit it. Conflicting results could be due to differences in the algal host condition: health and age of specimen and differences in the species of Gambierdiscus used for the investigations. 

One of the most important findings was the indication that Gambierdiscus Toxicus may change from being in an epiphytic state to free-swimming: in response to a change in the chemical environment around/on the host’s surface. Cell attachment and detachment were evident in the algal host Siphonous sp. and in several other species, some of which were: Dasya sp. and Martensia fragilis. Where Gambierdiscus was observed to change it's 'behaviour', the algal hosts were found to be producing chemical defences against herbivory, releasing chemical cues affecting the dinoflagellates.  

Ciguatera Fish Poisoning (CPF) is particularly interesting due to the perplexing symptoms; which can be bouts of recurring neurological disorders, affecting sufferers for a lifetime. I selected this paper because I wanted to explore an instigating factor behind the phenomenon of CPF: the dinoflagellate Gambierdiscus toxicus. The research carried out by Parson et al. 2011, relates to Randall’s new surface theory (Randall. 1958): which states that ‘newly denuded coral surface will be colonized by opportunistic algae’. Due to environmental changes: coral bleaching incidents are believed to be on the rise. Outbreaks of CFP could potentially become more frequent. Therefore it may be beneficial to further investigate the conditions that lead Gambierdiscus toxicus to change between stages of epiphytic and planktonic. This may yield more information as to what conditions affect dinoflagellate growth and possibly allow dinoflagellate ‘blooms’ to be anticipated.

Parson, M. L., Settlemier, C.J. and Ballauer, J. M. (2011)

"An examination of the epiphytic nature of Gambierdiscus toxicus, a dinoflagellate involved in ciguatera   fish poisoning"

  

Harmful Algae, 10: 598-605.

 http://www.ncbi.nlm.nih.gov/pubmed/21966283

Friedman, M. A., Fleming, L. E., Fernandes, M., Bienfang, P., Schrank, K., Dickey, R., Bottein, M. Y., Backer, L., Ayyar, R., Weisman, R., Watkins, S., Granade, R. and Reich, A. (2008)

"Ciguatera Fish Poisoning: Treatment, Prevention and Management"

Mar. Drugs, 3: 456-479.   

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579736/

Lobel, P. S. (1979)

"Folk remedies for tropical fish poisoning in the Pacific"

Sea Frontiers, 25: 239-245.

Randall, J.E. (1958) 

"A review of ciguatera, tropical fish poisoning with a tentative explanation of its cause"

Bull. Mar. Sci. Gulf Carib. 8: 236–267.