The smaller your mouth,the longer your snout:predicting the snout length of Syngnathus acus,Centriscus scutatus and other pipette feeders

摘要

Like most ray-finned fishes (Actinopterygii),pipefishes (Syngnathoidei) feed by suction.Most pipefishes reach their prey by a rapid dorso-rotation of the head.In the present study,we analysed the feeding kinematics of the razor fish,Centriscus scutatus,and of the greater pipefish,Syngnathus acus in detail.We found capture times of as little as 4-6 ms for C.scutatus and 6-8 ms for S.acus.We then hypothesized that the long snout of pipefishes is optimal for such fast feeding.To test this,we implemented in a mathematical model the following considerations.To reach the prey as fast as possible,a low moment of inertia increases the head's angular speed,whereas a long snout decreases the angle over which the head must be turned.The model accurately predicted the snout lengths of a number of pipefishes.We found that the optimal snout length,with which a prey will be reached fastest,is inversely related to its cross-section.In spite of the small cross-section,the development of a long snout can be an evolutionary advantage because this reduces the time to approach the prey.