Ichthyotoxicity of gymnodinioid dinoflagellates: PUFA and superoxide effects in sheepshead minnow larvae and rainbow trout gill cells

Abstract

While 24 h exposure of sheepshead minnow fish larvae to purified monogalactosyl diglyceride (MGDG) lipids, containing octadecapentaenoic acid (OPA) exclusively or as a mixture of octadecatetraenoic acid, eicosapentaenoic acid, and OPA (OTA-EPA-OPA), caused sluggish swimming and gulping, it produced no mortalities even at concentrations up to 120 mg l -1 . In contrast, comparable concentrations and exposure times caused significant reductions in viability of rainbow trout gill cells. Pure EPA was the most harmful to gill cells (up to 98.5% viability loss in 60 h) followed by OPA-rich MGDG (45% loss), with OTA-rich MGDG (37% loss) the least toxic. OPA-pure MGDG was non-toxic to rainbow trout gill cells; however, surprisingly, pure palmitic acid was harmful (40% viability loss), and we conclude that gill cell line toxicity of the OPA-rich MGDG fraction was caused by admixture with palmitic acid. Screening of 15 Kareniaceae dinoflagellate species demonstrated that these species are low (on average 10 times less) producers of superoxide compared to the ichthyotoxic raphidophyte Chattonella marina. No mortality of sheepshead minnow fish larvae occurred when exposed to superoxide alone or superoxide combined with either OPA-rich MGDG or OTA-rich MGDG. Superoxide showed a slight impact on viability of rainbow trout gill cells. In conclusion, synergistic interactions between free fatty acids and reactive oxygen species as previously claimed for raphidophytes could not be confirmed. Gill damaging effects from EPA were conclusively demonstrated, however; when these co-occurred with OTA, a higher loss of viability was observed (up to 37%), suggesting a magnified toxic effect. Contradictory literature claims as to the ichthyotoxicity of OPA (nontoxic in our work) may relate to the presence of chemical impurities.KEY WORDS: Kareniaceae · Ichthyotoxicity · Octadecapentaenoic acid · OPA · Polyunsaturated fatty acid · PUFA· Superoxide Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 426: [213][214][215][216][217][218][219][220][221][222][223][224] 2011 function, as these molecules remain fluid at lower temperatures (Valentine & Valentine 2004). Using bioassay-guided fractionation, the most common PUFAs investigated for toxic activity are octadecatetraenoic acid (OTA), octadecapentaenoic acid (OPA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). These molecules are highly reactive, contain 4 to 6 double bonds, and are short-lived in the water column (Jüt-tner 2001). PUFAs are synthesized almost entirely in the plastid, with the majority of OPA and OTA present in plastid-related glycolipids, as mono-or digalactosyl diglycerides (MGDG and DGDG) (Bell et al. 1997, Leblond & Lasiter 2009, and with EPA and DHA dominant in the cell-membrane phospholipid fraction (Leblond & Chapman 2000, Adolf et al. 2007). Upon lysis of senescent cells and/or dinoflagellate cell implosion upon contact with fish gills, the algal cells may rupture and release a cocktail of reactive...

Mortalities of sea-cage salmon (Oncorhynchus tshawytscha) due to a bloom of Pseudochattonella verruculosa (Dictyochophyceae) in Queen Charlotte Sound, New Zealand

“…However, this is unlikely to be a factor in the Ruakaka Bay bloom since irradiance levels while fish kills were occurring were very low. Recently some doubts regarding the role of superoxide and free fatty acids interaction have been raised through studies on ichthyotoxic gymnodinoid dinoflagellates (Mooney et al, 2011).…”

Karenia: The biology and ecology of a toxic genus

“…K. brevis and K. mikimotoi were among the larger producers of superoxide. Interestingly, the raphidophytes Chattonella antigua, Chattonella marina, Heterosigma akashiwo, and Fibrocapsa japonica that also produce brevetoxin, produce large amounts of superoxide in even higher concentrations (Mooney et al, 2011).…”

Progress in Understanding Harmful Algal Blooms: Paradigm Shifts and New Technologies for Research, Monitoring, and Management

“…Chattonella marina (Oda et al 1992), but this has not been substantiated by fish bioassays with chemically generated superoxide or hydrogen peroxide (Marshall et al 2003; Woo et al 2006). Other research groups have focused on PUFA as toxic agents (Gentien et al 2007), but with highly variable results, some of which have now been attributed to the incidence of uncharacterized lipid degradation products (Mooney et al 2011). …”

“…An important recent breakthrough has been the development of a standard fish gill bioassay system, which has been adapted for use with living algal cultures and lends itself to automation in a plate reader system measuring cell viability indicator dyes (Dorantes-Aranda et al 2011). It now is becoming clear that algal cells must rupture for significant ichthyotoxicity to occur, that some PUFAs such as EPA but not OPA nor OTA, can cause significant gill damage, and that ROS sometimes may be involved in the generation of highly toxic lipid peroxidation products (Marshall et al 2003, Mooney et al 2011). Hopefully, improved understanding of HAB fish killing mechanisms in future may aid in the design of effective mitigation strategies.…”