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

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Abstract
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