The effects of acute and chronic exposure of ammonia on juvenile burbot (Lota lota) growth and survival

Abstract

Burbot, Lota lota are a candidate species for commercial aquaculture because of their palatability and optimal growth at temperatures similar to those used in freshwater trout aquaculture. However, data on burbot environmental tolerances and requirements are sparse, especially with reference to water quality parameters relevant to aquaculture, such as un-ionized ammonia (UIA) concentration. We used a two-phased approach to evaluate the effects of un-ionized ammonia on the growth and survival of burbot. First, we measured the acute toxicity of ammonia to juvenile burbot (mean SL: 144 ± 6 mm; mean wet weight: 27.3 ± 3.4 g) and calculated a 96-h LC50 of 0.58 mg·L−1 UIA. We then measured the 60-d growth, food consumption rate, and performance of burbot (mean initial SL: 190 ± 6.9 mm; mean initial weight: 67.0 ± 4.5 g) reared in 0.00, 0.03, 0.06, 0.12, or 0.19 mg·L−1 UIA using a 20-tank flow-through system under optimal temperature (14.7 °C) and dissolved oxygen (DO >80% saturation) conditions. Elevated ammonia concentration significantly reduced daily food consumption and subsequent growth. Fish exposed to 0.03 and 0.06 mg·L−1 UIA showed temporal acclimation to UIA, achieving food consumption and growth rates on par with control fish after 30 days of exposure. The estimated effective UIA concentrations for 10 and 20% reductions in growth (EC10 and EC20) based on our data are: EC10 = 0.03 ± 0.006 mg·L−1 and EC20 = 0.050 ± 0.004 mg·L−1. We recommend rearing burbot under conditions that keep UIA levels ≤0.03 mg·L−1 based on our finding that above 0.03 mg·L−1 cause measurable reductions in growth rate.