Methodology
Yolk-sac fry were collected from male-defended nests and held in running water aquaria at the Queen's University Biology Station on Lake Opinicon, Chaffey's Locks, Ontario, Canada. Once the free swimming stage was reached the fry were redistributed amongst several holding aquaria or placed under experimentation. All fry were aged from the date that 50% of the yolk-sac fry of an aquarium became free swimming.
Fry in the holding aquaria were fed three times daily on live zooplankton from fertilized rearing pools and live brine shrimp nauplii. Once the fry were large enough, frozen brine shrimp was fed. All holding and experimental containers were cleared of accumulated debris two or three times daily. The 100 L holding aquaria were made of grey-painted wood with one glass side. All aquaria were supplied with lake water (alkalinity 65 mg/L as CaCO3, (Smol, 1984); pH = 7.7) and a natural photoperiod. The water temperature fluctuated from 18°C up to 24°C.