Relation between fish morphological differentiation and pressure drag difference

Abstract

Changes in the flow environment can cause changes in fish morphology, but the specific mechanisms by which flows change fish morphology are not known. It would be a useful addition to the field if it could be explored from the point of view of resistance properties. To explore the effect of water flowing over the fish surface, we selected Schizothorax prenanti as a representative species in flowing water and Carassius auratus as a representative fish in slow-moving water and carried out hydrodynamic experiments and numerical simulations without any simplification of the fish body in order to obtain accurate resistance data. The results show that in the simulated flow rate scenarios, the overall resistance of C. auratus and the local resistance at the head, dorsal, lateral, and hypogastrium regions were all higher, with maximum differences of 3.49 times, 3.63 times, 6.47 times, 10.41 times, and 46.77 times those of S. prenanti, respectively. Combining the results of this study with the theory of biomechanical adaptation, we believe that resistance characteristics are important factors in the shaping of fish body shape by water flow. On this basis we believe that in addition to ensuring the integrity of fish life histories, the resistance characteristics of individuals in natural streams need to be measured and recorded. Habitat restoration should provide similar resistance environments for protected species to avoid loss of shape characteristics.