The effect of spine postures on the hydrodynamic drag in Epinephelus ongus larvae

Abstract

Laboratory behavioural observation and computational fluid dynamics (CFD) analysis were conducted to examine whether the movement of the elongated dorsal and pelvic spines changed the hydrodynamic drag in white-streaked grouper Epinephelus ongus larvae. The behavioural observation in the tank revealed that the larvae extended the dorsal and pelvic spines during passive transport and retracted during swimming; the angles of the dorsal and pelvic spines in relation to the anteroposterior axis were larger during the passive transport (mean ± S.D. = 28.84 ± 14.27 and 20.35 ± 15.05°) than those during the swimming (mean ± S.D. = 2.59 ± 5.55 and 0.32 ± 6.49°). The CFD analysis indicated that the relative hydrodynamic drag acting on the larvae was approximately 1.25 times higher when the spines were extended (passive transport) than when the spines were retracted (swimming), suggesting that the E. ongus larvae have an ability to adjust their hydrodynamic drag depending on the behavioural context.

Antipredator tactics: a kin‐selection benefit for defensive spines in coral catfish?

“…The most plausible ‘cost' involves hydrodynamics. Minor variations in the shape of fins and spines can affect hydrodynamic drag (Lauder and Drucker 2004, Kawabata et al 2014), increasing costs of locomotion. In populations of channel catfish maintained in captivity over several generations (and thus, no longer exposed to predators), the length of defensive spines exhibited a rapid decrease that was caused by adaptation rather than by phenotypic plasticity (Duvall 2007, Fine et al 2011a, 2014).…”