Induced sustained swimming modifies the external morphology, increasing the oxygen-carrying capacity and plasma lactate levels of juvenile gilthead seabream (Sparus aurata) without changing fish performance or skeletal muscle characteristics

Abstract

Some species of fish can be induced to swim under optimal conditions aiming to improve their growth performance and welfare. This study was undertaken to investigate the effects of induced sustained swimming on the growth performance, metabolic parameters [standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS), and excess post-exercise oxygen consumption (EPOC)], external morphology, skeletal muscle fiber characteristics and distribution of juvenile gilthead seabream (Sparus aurata), as well as immune and metabolic markers. Fish with a body mass of 26.89 ± 0.26 g and a total length of 12.27 ± 0.04 cm were induced to swim continuously at 1.1 body lengths s−1 (S group) or maintained under minimal water flow with fish displaying spontaneous swimming activity (C group) for 13 weeks. The water current in the S group was maintained at a similar level and by the end of the trial; the swimming speed was 0.8 body lengths s−1. Long-term induced swimming activity had no significant effect on the growth rate, feed efficiency, or red and white muscle cross-sectional area, fiber diameter, and density. However, swimming significantly changed the body shape of gilthead seabream, with the S group having shallower bodies, more pronounced nuchal humps, flatter abdomens, and larger caudal fins compared with the C group. SMR, MMR, AAS, and EPOC were similar in both experimental groups. Hematocrit and plasma lactate levels were significantly higher in the S group, whereas plasma glucose, protease, and anti-protease activities were not different between both groups. Despite the lack of changes in growth performance, feed efficiency, skeletal muscle morphological traits, and metabolic rates, induced swimming changed the body shape of seabream, and increased the oxygen-carrying capacity and plasma lactate levels.