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 (LT) and quadratic in mass. Dorsal swimbladder area increased exponentially with LT. Allometric growth ratio (i.e. k) values of swimbladder length linearly increased with LT. Average swimbladder volumes occupied 3–6% of fish body volume and increased exponentially with LT. The aspect angle that resulted in the maximum average acoustic intensity from the group shifted from 80 to 86° through the experimental period. Mean echo intensities increased at both 38 and 120 kHz as mean LT increased. Predicted echo intensities at 38 kHz exceeded that at 120 kHz at LT 280 mm. Generalized additive mixed models using LT, swimbladder angles and lateral elongation ratios of fish bodies were better predictors of echo intensities than LT alone.