Ciguatera fish poisoning (CFP) is a foodborne disease caused by the consumption of seafood (fish and marine invertebrates) contaminated with ciguatoxins (CTXs) produced by dinoflagellates in the genus Gambierdiscus. The report of a CFP-like mass-poisoning outbreak following the consumption of Tectus niloticus (Tegulidae, Gastropod) from Anaho Bay on Nuku Hiva Island (Marquesas archipelago, French Polynesia) prompted field investigations to assess the presence of CTXs in T. niloticus. Samples were collected from Anaho Bay, 1, 6 and 28 months after this poisoning outbreak, as well as in Taiohae and Taipivai bays. Toxicity analysis using the neuroblastoma cell-based assay (CBA-N2a) detected the presence of CTXs only in Anaho Bay T. niloticus samples. This is consistent with qPCR results on window screen samples indicating the presence of Gambierdiscus communities dominated by the species G. polynesiensis in Anaho Bay. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses revealed that P-CTX-3B was the major congener, followed by P-CTX-3C, P-CTX-4A and P-CTX-4B in toxic samples. Between July 2014 and November 2016, toxin content in T. niloticus progressively decreased, but was consistently above the safety limit recommended for human consumption. This study confirms for the first time T. niloticus as a novel vector of CFP in French Polynesia.

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Ciguatera Fish Poisoning (CFP) is a foodborne disease classically related to the consumption of tropical coral reef fishes contaminated with ciguatoxins (CTXs), neurotoxins produced by dinoflagellates of the Gambierdiscus genus. Severe atypical ciguatera-like incidents involving giant clams, a marine resource highly consumed in the South Pacific, are also frequently reported in many Pacific Islands Countries and Territories. The present study was designed to assess the ability of giant clams to accumulate CTXs in their tissues and highlight the potential health risks associated with their consumption. Since giant clams are likely to be exposed to both free-swimming Gambierdiscus cells and dissolved CTXs in natural environment, ex situ contamination experiments were conducted as follows: giant clams were exposed to live or lyzed cells of TB92, a highly toxic strain of G. polynesiensis containing 5.83±0.85pg P-CTX-3C equiv.cellvs. HIT0, a weakly toxic strain of G. toxicus containing only (2.05±1.16)×10pg P-CTX-3C equiv.cell, administered over a 48h period at a concentration of 150cellsmL. The presence of CTXs in giant clams tissues was further assessed using the mouse neuroblastoma cell-based assay (CBA-N2a). Results showed that giant clams exposed to either lyzed or live cells of TB92 were able to bioaccumulate CTXs at concentrations well above the safety limit recommended for human consumption, i.e. 3.28±1.37 and 2.92±1.03ng P-CTX-3C equiv.g flesh (wet weight), respectively, which represented approximately 3% of the total toxin load administered to the animals. In contrast, giant clams exposed to live or lyzed cells of HIT0 were found to be free of toxins, suggesting that in the nature, the risk of contamination of these bivalves is established only in the presence of highly toxic blooms of Gambierdiscus. Liquid chromatography-mass spectrometry (LC-MS/MS) analyses confirmed CBA-N2a results and also revealed that P-CTX-3B was the major CTX congener retained in the tissues of giant clams fed with TB92 cells. To the best of our knowledge, this study is the first to provide evidence of the bioaccumulation of Gambierdiscus CTXs in giant clams and confirms that these bivalve molluscs can actually constitute another pathway in ciguatera poisonings. While most monitoring programs currently focus on fish toxicity, these findings stress the importance of a concomitant surveillance of these marine invertebrates in applicable locations for an accurate assessment of ciguatera risk.

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Feeding motivation is one major indicator of fish welfare and an investigation on the link between feed demand, growth and physiological variables in sea bass juveniles was developed. A computerized ondemand feeding system coupled with a PIT tag monitoring device was used to continuously record for 219 days the triggering activity of 150 individuals (initial average body weight 131.6 ± 1.80 g and coefficient of variation 16.8%). Each group was held in 400 l tanks at 22.2 ± 1.5 °C and light regime was 16:8 LD. In all the tanks, 89% of the fish actuated the trigger, but only two or three fish accounted for 45% of the total triggering activity. These few high-triggering individuals had a transient higher growth i.e. at the time an individual was the high-triggering fish in the tank, its Specific Growth Rate (SGR) increased and was higher than that of the other fish. However, high-triggering fish did not exhibit a higher initial and final body weight nor a higher average SGR than low-and zero-triggering fish. Fish of different triggering categories did not show differences in physiological variables (muscle composition, blood and tissues biochemistry). This study also revealed that when an imbalance between apparent daily feed tank consumption and feed demand was observed (i.e. wastage), it was mostly due to an increasing demand rather than a decreasing consumption; such wastage could often be linked to particular stressors (measuring day, population sampling or social interactions) and therefore, feeding motivation disturbances could be a relevant operational fish welfare indicator.