The effects of diatom polyunsaturated aldehydes on embryonic and larval zebrafish (Danio rerio)

Marine diatoms are pervasive in many planktonic and benthic environments and represent an important food source for a wide range of species. Some diatoms produce polyunsaturated aldehydes (PUAs) as defensive toxins. PUA exposure is known to reduce the fecundity of invertebrate grazers like copepods and echinoderm larvae, but little is known about the effects of PUAs on vertebrates. Many fish species are likely to come into close contact with diatoms. Many may deposit eggs on diatom-coated substrates, consume diatoms as larvae, and/or feed heavily on zooplankters that may be gut-loaded with diatoms. The purpose of this study was to test whether dissolved diatom PUAs affect the early life stages of a model fish, Danio rerio (zebrafish). To test this, zebrafish embryos and larvae were exposed to proportionally increasing mixtures of the dissolved diatom PUAs 2E,4E-decadienal, 2E,4E-octadienal and 2E,4E-heptadienal. Under PUA exposure, three metrics of fitness were assessed: embryo heart rate, larval size at hatch, and pre-feeding mortality rate. Zebrafish embryos exposed at 24 h post fertilization (hpf) experienced decreased average heart rate after 2 days of PUA exposure. Embryos 24 hpf exposed to PUA mixtures for 6 days showed a reduction in size in comparison to embryos from controls. Embryos exposed to PUAs from 2 hpf until death showed lower survivorship compared to larvae in controls. The results of this study suggest that larval fish that are sympatric with PUA producing diatoms during their embryonic and larval stages may be susceptible to detrimental effects from PUA exposure.