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Ciguatoxins (CTXs), produced by toxic benthic dinoflagellates, can bioaccumulate in marine organisms at higher trophic levels. The current study evaluated the uptake and depuration kinetics of some of the most potent CTXs, Pacific CTX-1, -2, and -3 (P-CTX-1, -2, and -3), in orange-spotted grouper (Epinephelus coioides) exposed to 1 ng P-CTXs g −1 fish daily. Over a 30 d exposure, P-CTX-1, -2, and -3 were consistently detected in various tissues of exposed fish, and the concentrations of the total P-CTXs in tissues generally ranked following the order of liver, intestine, gill, skin, brain, and muscle. Relatively higher uptake rates of P-CTX-1 in the groupers were observed compared with those of P-CTX-2 and -3. The depuration rate constants of P-CTX-1, -2, and -3 in different tissues were (0.996−16.5) × 10 −2 , (1.51−16.1) × 10 −2 , and (0.557−10.6) × 10 −2 d −1 , respectively. The accumulation efficiencies of P-CTX-1, -2, and -3 in whole groupers were 6.13%, 2.61%, and 1.15%, respectively. The increasing proportion of P-CTX-1 and the decreasing proportion of P-CTX-2 and -3 over the exposure phase suggest a likely biotransformation of P-CTX-2 and -3 to P-CTX-1, leading to higher levels of P-CTX-1 in fish and possibly a higher risk of CTXs in long-term exposed fish.

Marine heterotrophic microalgal species which are potentially rich in docosahexaenoic acid (DHA, C22:6n-3) have been found in Taiwan; however, there was a lack of detailed analysis and characterization of these indigenous algae which is needed for the development of commercial applications. Hence, the objective of this study was to screen DHA-rich heterotrophic microalgae species indigenous to Taiwan for commercial purposes. Heterotrophic microalgae from a variety of marine habitats were isolated, cultivated, and then identified according to their 18S rRNA gene sequences and morphological characteristics. A comparison was made of their fatty acid profiles, fatty acid content, and amount of biomass. For the strain with highest DHA yield, the optimal growth conditions were determined in order to establish the best fermentation conditions for scale-up. In this study, 25 heterotrophic microalgal strains were successfully isolated from marine habitats around Taiwan. All of the isolated strains showed a close phylogenic relationship with the Thraustochytriaceae family according to their 18S rRNA gene sequences. GC/MS analysis discerned seven distinctive fatty acid profiles of these strains, with the production of eicosapentaenoic acid (C20:5n-3) ranging from 0.02 to 2.61 mg L(-1), and DHA ranging from 0.8 to 18.0 mg L(-1). An Aurantiochytrium strain BL10 with high DHA production was subsequently chosen for further manipulation. Under optimal growth conditions it could produce up to 59.0 g of dry biomass per liter of culture, with dry biomass containing 73% total fatty acid and 29% DHA, revealing BL10 as an excellent source of microbial DHA.

Polyunsaturated fatty acids (PUFAs) are fatty acids with more than one double bond in the chemical structure. Arachidonic acid (ARA, 20:4 (n-6)) and eicosapentaenoic acid (EPA, 22:5 (n-3)) are common PUFAs with beneficial health effects. Marine fish and meat are the main sources of omega-3 and omega-6 fatty acids in human's diet, respectively. In particular, there is a general decline in fish catch, implicating the need for an alternative source of omega-3 fatty acids. Previous studies have examined the production of polyunsaturated fatty acids including ARA and EPA by various microorganisms, including microalgae, fungi, and thraustochytrids. In this study, the production of ARA and EPA by 10 isolates of four estuarine Halophytophthora species (Halophytophthora avicenniae, Halophytophthora polymorphica, Halophytophthora vesicula, and Halophytophthora spinosa var. spinosa) cultured from fallen mangrove leaves in Taiwan was examined. The yield of ARA ranged from 0.004 to 0.052 g/L with the highest yield of ARA obtained from H. spinosa var. spinosa IMB162, but no or a very low level of EPA was produced by IMB162. For EPA production by Halophytophthora spp., the yield ranged from 0 to 0.047 g/L. Percentage of ARA in total fatty acid ranged between 7.16 and 25.02%. One-way ANOVA analysis using Tukey Test (p ≥ 0.05) suggested that there is significant difference in the percentage of EPA in total fatty acid produced by the isolates, which ranged from 0.01 to 18.42%. BODIPY 505/515 fluorescent staining suggests that lipid bodies were evenly distributed in the mycelia of Halophytophthora species.