Acoustic ontogeny of a teleost

The influence of growth on the intensity and variability of acoustic echoes from individuals and groups of a teleosts was quantified using Donaldson trout (rainbow-steelhead hybrid) Oncorhynchus mykiss. Fish growth was linear in total length (L-T) and quadratic in mass. Dorsal swimbladder area increased exponentially with L-T. Allometric growth ratio (i.e. k) values of swimbladder length linearly increased with L-T. Average swimbladder volumes occupied 3-6% of fish body volume and increased exponentially with L-T. The aspect angle that resulted in the maximum average acoustic intensity from the group shifted from 80 to 86 degrees through the experimental period. Mean echo intensities increased at both 38 and 120 kHz as mean L-T increased. Predicted echo intensities at 38 kHz exceeded that at 120 kHz at L-T < 150 mm but were less than that predicted at 120 kHz at L-T > 280 mm. Generalized additive mixed models using L-T, swimbladder angles and lateral elongation ratios of fish bodies were better predictors of echo intensities than L-T alone. (C) 2008 The Author Journal compilation (C) 2008 The Fisheries Society of the British Isles