Enhancement of the Survival of Rainbow Trout (Salmo gairdneri) Eggs and Fry in an Acid Lake through Incubation in Limestone

Incubation of eyed rainbow trout (Salmo gairdneri) eggs within boxes (60 × 60 × 30 cm) of crushed limestone enhanced hatching success and sac fry surival in acidic (pH ~5.3) George Lake. Hatching (egg–sac fry) success in limestone (86.9%) along a sheltered shoreline (interstitial pH 6.2–7.6) approached results in Fairbank, a near-neutral control lake (93.7–97.9%). Eggs incubated in limestone along a windswept shoreline and subjected to periodic depression of interstitial water pH (minimum recorded 5.6) due to wave action exhibited poor hatching success (57.4%) comparable to results (11.2–57.1%) for eggs exposed within substrates of mixed, noncalcareous gravel (minimum pH 5.2–5.4). Sac fry survival (sac fry alevins) was high in sheltered limestone substrates (70.9%), low in wind-exposed limestone substrates (23.2%), and very poor (0.2–0.4%) in noncalcareous gravel.Exposure to emergent alevins hatched within limestone to ambient, acidic lake water resulted in 65.2–78.8% mortality during a 5-d holding period. Mortality decreased greatly among alevins held at pH 5.6–5.9 (48.0%) and pH 6.1–6.3 (2.0%)Incubation of eggs within limestone substrates holds promise for use as a tool in the maintenance of salmonid populations in acidic lakes. Key words : rainbow trout, pH, limestone, acidic lake