Integrated water quality and toxin-induced selection pressure monitoring using a model fish, the Japanese medaka, in the Albemarle-Pamlico Sound region

Background/Question/Methods   The Albemarle-Pamlico Sound represents the most active area of fisheries in North Carolina, boasting the blue crab fishery as well as flounder, oysters, clams, mullet, and shrimp fisheries. Most of the fishermen are artisinal and often run one-man operations cycling through the different species at different times of the year. During previous work addressing perceptions of environmental change among the fisher community, the issue of declining water quality played a prominent role. Water quality degradation in the upper stretches of the Albemarle, where I interviewed the fishermen, is likely due to farm runoff, industrial effluent from a paper mill, and septic tank leachates. Chemicals of concern primarily include pesticides and pharmaceuticals, as fishers report finding dead fish or areas of “dead water” after nearby farms are sprayed with either pesticides or fertilizers. These chemicals in high concentrations can be acutely toxic, causing the mortality observed by the fishers but also likely exist at lower chronic doses affecting the fishery long-term through nonlethal secondary effects. These effects include intersexed fish, decreased fertility, and disrupted communication. To test the theories of water quality discussed by the fishers, I used a model fish in ecotoxicology, the Japanese medaka (Oryzias latipes), which allows the use of a complete genome sequence and tightly controlled multi-generational exposures. Their development and endocrine system has also been extensively studied. Medaka embryos were reared in water from the Albemarle-Pamlico estuary system identified by fishers as areas they had observed potential toxin issues in fishery species.

Results/Conclusions   Some of these sites yielded high mortality and developmental abnormalities, most notably the areas directly downstream of cotton fields and near major roads. The types of abnormalities observed (premature hatching, skeletal deformations, failure to feed, circulatory system issues, failure of swim bladder to inflate, and infertile males) suggest endocrine disruption is occurring, which has direct implications for population dynamics of fishery species. In addition, the high mortality and presence of infertile males suggest there is likely strong selection pressure on resident species to resist the effects of these toxins. This resistance may come at the cost of fishery productivity.