Trophic transfer, tissue distribution, and neurotoxic consequences of the phycotoxin, domoic acid, in northern anchovies (Engraulis mordax) (California)

Over the past decade the consumption of planktivorous northern anchovies containing the diatom-produced neurotoxin, domoic acid (DA), has been responsible for severe neurologic illness and mass mortality events involving hundreds of sea birds and marine mammals in Monterey Bay, California. This research characterizes the dynamics of DA transfer, accumulation, and neurotoxicity in this pivotal and dangerous DA vector fish species. Chapter one documents a DA-poisoning event in which dozens of California sea lions died as a result of consuming DA-contaminated anchovies in Monterey Bay. DA levels in sea lion feces and anchovies were attained using HPLC-UV and microplate receptor binding assays, with absolute confirmation by tandem mass spectrometry. The presence of toxic Pseudo-nitzschia frustules in sea lion feces and anchovy gut contents was determined using scanning electron microscopy. Chapter two presents data from an intracoelomic injection study in which anchovies were shown to be neurologically susceptible to DA excitotoxicity and to have a similar sensitivity to the toxin as mammals. Excitotoxic symptoms are described and confirm that DA crosses the blood brain barrier in fish. Chapter three characterizes the dynamics of DA accumulation in small planktivorous fish in relation to ecologically relevant toxic diatom densities. Toxic Pseudo-nitzschia densities and DA levels in anchovies and sardines were measured from samples collected weekly throughout Monterey Bay from 10/8/99 to 10/8/00. DA levels in fish were estimated via HPLC-UV and toxic cell densities were determined via whole cell hybridization with species-specific large subunit rRNA-targeted fluorescent probes. DA levels accumulated in fish viscera tracked toxic cell densities in surface waters confirming that anchovies and sardines regularly consume toxic diatoms when present in Monterey Bay. Fish viscera DA levels harmful to piscivorous predators occurred when toxic cell densities exceeded 104 cells liter−1. Anchovies accumulated more DA than sardines in viscera, however neither species appears to accumulate significant levels of toxin in body tissue. Finally, Appendix A includes results from histologic examination of brain sections taken from control and DA-intoxicated anchovies and stained with haemotoxylin and eosin dyes. Although intoxicated fish exhibited seizures, brain lesions characteristic of DA excitotoxicity were not found.