Meeting Abstract

33.1  Wednesday, Jan. 5  Feeding mechanics in billfishes (Xiphiidae and Istiophoridae): inferring the use of the bill from its mechanical properties HABEGGER, Maria Laura*; MOTTA, Philip J; MULLINS, Gray; STOKES, Michael; WINTERS, Daniel; University of South Florida mhabegge@mail.usf.edu

Billfish are perciform fishes characterized for the presence of an elongated rostrum or “bill” composed mostly of the premaxillary bones. Despite the prominence of this structure, for which this group is named, the function of the rostrum remains controversial. Previous works suggest that the bill may enhance billfish hydrodynamics, or serve as a tool for defense. However, these hypotheses have not been tested. An alternative hypothesis involves the use of the rostrum during feeding, where billfish may stun or kill their prey by hitting it with the rostrum before ingestion. Additionally, species with different bill morphologies may attack prey by moving the rostrum in different planes. The goal of this study is to characterize the structure and compare the mechanical properties of the rostrum in two species of billfishes with different bill morphologies, blue marlin (Makaira nigricans) and swordfish (Xiphias gladius) in order to quantify the mechanical capabilities and suggest a biological role for the rostrum. Mechanical variables such as stress, strain and second moment of area will be estimated along five points of the bill using theoretical and experimental approaches for both species. Additionally, histological samples will be obtained in order to characterize the components that constitute the rostrum in billfish.