Effects of chronic ammonia exposure on growth and food conversion efficiency in juvenile spotted wolffish

Abstract

The effects of chronic un-ionised ammonia (UIA) exposure on growth and food conversion efficiency (FCE) in spotted wolffish, Anarhichas minor Olafsen, were examined. Fish with a mean (S.D.) initial weight 14.2 (5.0) g were reared in shallow raceways (initial stocking density of 3.9 kg m −2) and exposed to four concentrations of UIA [0.0006 (control), 0.13 (low), 0.25 (medium) and 0.39 mg l −1 (high)] for 69 days at 8.3 °C, 33‰ and pH 8.1. Growth rates were significantly influenced by UIA concentrations, as the control and low-concentration group performed better than both the medium- and high-concentration group, and the medium group in turn displayed a higher growth rate than the high-concentration group throughout the experimental period. While experiencing negative growth rates in the first period, growth rates increased and were positive in fish from both the medium and high group in the second and third period, indicating an adaptation to ambient UIA. At the end of the experiment, mean weights were 13% and 40% lower at UIA concentrations of 0.13 and 0.25 mg l −1, respectively, when compared to the control group, whereas an overall decrease in mean weight was observed at 0.39 mg UIA l −1 in the experimental period investigated. The difference in growth performance is mainly attributed to variations in daily feed consumption, which varied significantly between all treatments throughout the experiment and decreased with increasing concentrations of UIA, and to a lesser extent by a decrease in food conversion efficiency.