Body Form, Locomotion and Foraging in Aquatic Vertebrates

TLDR

Aquatic vertebrates exhibit four locomotor categories—BCF periodic, BCF transient, MPF, and occasional—whose specialization limits performance in other modes, and food acquisition depends on spatial distribution and evasiveness, with smaller fish acting as generalists under predation pressure. BCF periodic swimmers capture widely dispersed food, BCF transient swimmers target locally abundant evasive prey, MPF swimmers take non‑evasive food in complex habitats, specialists under‑utilize small items in exposed areas, and generalists rely less on locomotor adaptations, favoring suction and protrusible jaws.

Abstract

Four functional categories are denned to embrace the range of locomotor diversity of aquatic vertebrates; (1) body/caudal fin (BCF) periodic propulsion where locomotor movements repeat, as occurs in cruising and sprint swimming; (2) BCF transient propulsion where kinematics are brief and non-cylic, as occurs in fast-starts and powered turns; (3) median and paired fin (MPF) propulsion, with very diverse fin kinematics, used in slow swimming and precise maneuver; (4) occasional propulsion or "non-swimming." Specialization in any one of these categories compromises performance in one or more of the others, thereby reducing locomotor diversity and hence behavioral options. Food characteristics influencing the role of locomotion in search and capture are; (1) distribution in space and/or time and (2) evasive capabilities. BCF periodic swimmers take food that is widely dispersed in space/time; BCF transient swimmers consume locally abundant evasive items and MPF swimmers consume non-evasive food in structurally complex habitats. Locomotor specialists under-utilize smaller food items in exposed habitats. This resource is exploited by smaller fish, which are locomotor generalists because of predation pressures. For such locomotor generalists, locomotor adaptations for food capture are of diminished importance and other adaptations such as suction and protrusible jaws in fish are common.