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In the coastal countries of Southeast Asia, fish is a staple diet and certain fish species are food delicacies to local populations or commercially important to individual communities. Although there have been several suspected cases of ciguatera fish poisoning (CFP) in Southeast Asian countries, few have been confirmed by ciguatoxins identification, resulting in limited information for the correct diagnosis of this food-borne disease. In the present study, ciguatoxin-1B (CTX-1B) in red snapper (Lutjanus bohar) implicated in a CFP case in Sabah, Malaysia, in December 2017 was determined by single-quadrupole selected ion monitoring (SIM) liquid chromatography/mass spectrometry (LC/MS). Continuous consumption of the toxic fish likely resulted in CFP, even when the toxin concentration in the fish consumed was low. The identification of the fish species was performed using the molecular characterization of the mitochondrial cytochrome c oxidase subunit I gene marker, with a phylogenetic analysis of the genus Lutjanus. This is the first report identifying the causative toxin in fish-implicated CFP in Malaysia.

Neurotoxic poisonings with fatal symptoms caused by consumption of Nassarius gastropods have been reported in Vietnam but the causative toxins have not been confirmed. In the present study, Nassarius conoidalis, N. glans and N. pullus, which are considered to be common causative species, were collected in Khanh Hoa province, Vietnam in May 2016 for toxin analysis using LC/MS/MS. The results confirmed that TTX is a dominant toxin in these gastropods. Among them, N. glans exhibited the highest toxicity (412.7 ± 107.3 MU/g), followed by N. conoidalis (144.8 ± 82.0 MU/g) and N. pullus (19.6 ± 9.8 MU/g). This is the first report confirming TTX in these species. All specimens in this study were hightly toxic, indicating that the frequency of toxic specimens of the three Nassarius species is extremely high. Further, their toxicities were all beyond the regulatory level of consumption (10 MU/g) for puffer(fish) as recommended in Japan. The present data indicates that N. conoidalis, N. glans and N. pullus are not suitable for food in Vietnam.

Meadia minor sp. nov., a scaless ilyophine eel, is described on the basis of 10 specimens collected from off Quy Nhon, central coast of Vietnam. It can be distinguished from its congeners in having a relatively long trunk (21.3–25.0% TL) which is longer than head length; a short and blunt snout (21.4–23.7% HL); gill opening close to pectoral-fin base; interbranchial space broad (20.7–26.2% HL); dorsal-fin origin above posterior third of pectoral fin; body depth 24–28 times in TL; total vertebrae 118–122; mean vertebral formula 7-33-121; and a small body size, reaching 330 mm TL. The generic status of the new species is discussed. Short descriptions of two congeners are provided.

Two strains of Pseudo-nitzschia fukuyoi isolated from Vietnamese waters produce domoic acid, a toxin responsible for amnesic shellfish poisoning. Species identification was based on detailed morphological observation using a transmission electron microscope and also molecular data on large subunit (LSU) and the second internal transcribed spacer (ITS2) with NCBI nucleotide Blast (blastn). Toxin productivity of the two strains was confirmed and their range were 3.85–4.54 pg/cell by analyses using LC–MS/MS. This is the first report of occurrence of P. fukuyoi in Vietnamese waters, and the first confirmation of productivity of domoic acid of the species.

Three forms of gonadotropin-releasing hormone (GnRH) namely, salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and seabream GnRH (sbGnRH) were identified in the brain of Asian seabass Lates calcarifer using reverse-phase high performance liquid chromatography (rpHPLC) combined with time-resolved fluoroimmunoassay (TR-FIA) using rabbit polyclonal antibody raised against sGnRH, cGnRH-II and sbGnRH. An extract of L. calcarifer brain showed a similar retention time to that of synthetic sGnRH, cGnRH-II and sbGnRH on rpHPLC. In the brain, cGnRH-II and sGnRH levels were high, whereas sbGnRH was absolutely dominant in the pituitary. In addition, cGnRH-II, sGnRH and sbGnRH immunoreactive (ir) cell bodies and fibers in the brain and pituitary were also examined by immunohistochemistry. sGnRH-ir cell bodies were localised in the ventromedial part of the rostral olfactory bulb, terminal nerve ganglion region, and the transitional area between the olfactory bulb and telencephalon. cGnRH-II-ir cell bodies were located only in the midbrain tegmentum and sbGnRH-ir cell bodies were evident in the preoptic area. sGnRH-ir fibers were distributed throughout the brain, especially abundant in the forebrain. cGnRH-II-ir fibers were found in many parts of the brain, being more dense in the midbrain, whereas sbGnRH-ir fibers were localised in the preoptic-hypothalamic area, innervating the pituitary. In the pituitary, sbGnRH-ir fibers were profuse in the neurohypophysis and invaded the proximal pars distalis. These results confirm the existence of multiple GnRH forms with different physiological roles in L. calcarifer. Among them, sbGnRH is considered to be the best candidate for pituitary regulation while sGnRH and cGnRH-II can function as neurotransmtters or as neuromodulators in this species.

Previously we reported that a significant level of domoic acid, a causative toxin for amnesic shellfish poisoning, was detected in bivalves belonging to a genus Spondylus from various tropical Asian countries. These findings indicate that causative plankton species for domoic acid widely distribute in these areas. In the present study, we monitored seasonal change of domoic acid level of Spondylus versicolor in association with that of plankton samples in Nha Phu Bay, Khanh Hoa, Vietnam from December 2004 to October 2005. The toxicity of S. versicolor showed distinct seasonal variation. During the period when domoic acid level of S. versicolor was increasing, a significant level of domoic acid was detected in the plankton samples, showing the correlation between these two parameters. These findings show that plankton causative for domoic acid occurred in the bay, and S. versicolor accumulate domoic acid during a bloom of the toxic plankton by food web transfer.

Tetrodotoxin (TTX) was detected by HPLC and LC-MS/MS in specimens of the horseshoe crab Carcinoscorpius rotundicauda collected from Tan Hai village, Vung Tau province, Vietnam, where cases of poisoning due to the consumption of horseshoe crab have frequently been reported. The soft tissue from 10 out of the 12 specimens analyzed showed considerable levels of TTX, making them unsafe for human consumption (81.2 ± 50.3 MU/g). Paralytic shellfish poisoning (PSP) toxins were also detected in all of the specimens, but the levels were low. These findings show that the frequency of occurrence of C. rotundicauda specimens with a high level of TTX is significantly high, and that the TTX is responsible for the food poisonings caused by the consumption of C. rotundicauda in this area.