259 - Sewage effluent changes sexual organs and limits survivorship and larval mosquito feeding rates of Gambusia affinis

Mosquitofish, Gambusia affinis, are eponymous larval mosquito predators. Other than being water-bound, mosquitofish’s ability to survive low oxygen allow them to naturally manage larval mosquito populations in most ground pools where they are introduced. Effluent from onsite sewer disposal systems (OSDS, aka “septic systems”) has been shown to limit the presence of fish predators, releasing Culex quinquefasciatus larvae from suppression. Mosquitofish were collected and body conditions were compared in sites with and without effluent discharge from OSDS. Using mosquitofish from clean water sites, lethal doses of sewage effluent and time to 50% mortality were determined. Finally, prey capture rates were compared across three concentrations of OSDS effluent. Fish from contaminated sites were proportionally heavier than control fish and females from contaminated populations were masculinized. Sewage effluent had an LD50 at 71% concentration over 4 days and a LT50 of 25 hours at 90% concentration. In addition, mosquitofish generally stop feeding in high effluent concentration, though individual variation was observed. Effluent from OSDS reduces mosquitofish health, survival, and prey capture allowing West Nile virus vectors to thrive.