Morphology and metabolic traits related to swimming performance in Australasian snapper (Chrysophrys auratus) selected for fast growth.

Changes in body shape are linked to swimming performance and become relevant for selective breeding programmes in cultured finfish. We studied how the selection for fast growth could affect phenotypes by investigating the relationship between swimming performance and body shape. We also investigated how swimming might affect plasma metabolite concentrations. Critical swimming speed (U Crit ), body traits (e.g., BW, body weight; BL, body length; K, condition factor), and plasma lactate and glucose concentrations were evaluated in two cohorts of Australasian snapper (Chrysophrys auratus): one derived from wild broodstock (F 1 ), and the other selected for fast growth (F 4 ). U Crit tests (n = 8) were applied in groups of 10 snapper of similar BW (71.7 g) and BL (14.6 cm). The absolute or relative U Crit values of both cohorts were similar (0.702 m⋅s -1 and 4.795 BL⋅s -1 , respectively), despite the F 4 cohort displaying a higher K. A positive correlation between K and absolute U Crit (Pearson's r = 0.414) was detected in the F 4 cohort, but not in the F 1 cohort, which may be linked to differences in body shape. A negative correlation between relative U Crit and body size (Pearson's r between -0.682 and -0.501), but no correlation between absolute U Crit and body size, was displayed in both cohorts. Plasma lactate and glucose concentrations were higher in the F 4 cohort at U Crit . Whether a longer selective breeding programme could result in more changes in body shape, potentially affecting swimming performance, should be explored, along with the potential outcomes of the differences in metabolic traits detected.