Abstract:With extensive utilization of fishery resources, it is important to understand the related feeding habits of large marine predatory fish. In traditional studies on stomach contents, cephalopod organisms in the stomach of fish are identified mainly on the basis of cephalopod body characteristics. However, because the physical characteristics of cephalopods are affected by digestive juices in fish stomachs, the appearance of cephalopods are easily destroyed. Therefore, there are some limitations in the identification of cephalopods based on these characteristics. Cephalopod beaks have morphological characteristics that can be used for species identification and classification, but the classification of cephalopod beaks from stomach contents of large marine predatory fish has not yet been conducted. Thus, in order to investigate the possibility of classifying cephalopod beaks from stomach contents of six large marine predatory fishes, we examined a total of 36 fish stomachs from the South Atlantic, Middle East Pacific, and Western Indian Oceans in October 2017, March~May 2018, and November 2018, and analyzed cephalopod beak morphology. In this study, two-dimensional digital images of beak morphology were collected. The side and top morphologies of each lower beak were collected for species identification. Based on the morphological characteristics of the beak and the terminology related to beak morphology, a classification retrieval table for beak morphology was developed. The morphology coefficients were analyzed by clustering at the family level by extracting the elliptic Fourier descriptor coefficients of beak morphology. Results showed that a total of 17 species of cephalopods were found in two orders and ten families through species identification using beak morphology. Analysis of the beak morphology from stomach contents revealed that the morphological characteristics of the beaks of 17 species of cephalopods are clearly different among species. According to the classification retrieval of beak morphology, the lower beak of the rostrum of 13 species of Teuthoidea was triangular and isosceles triangle, and the lateral wall was approximately rhomboid. The wings were well-developed. The lower beak of the rostrum of four species of Octopoda was developed, and the lateral wall was approximately a long quadrangle. Wing development occurred. The morphology of beaks in different cephalopods has unique characteristics, and the characteristics of each species are very different, as indicated during the analysis. Cluster analysis of morphological information from beaks was effective for distinguishing cephalopods at the order level. In the cluster analysis, beak morphology was divided into two main parts: one mainly corresponded to Teuthoidea and the other corresponded to Octopoda. The identification and classification of beak morphology from stomach contents can be used as a marker for the biological identification of cephalopods. This not only can support the recognition of cephalopods from stomach contents, but also enrich the identification content of cephalopods from stomach contents. This study lays the foundation for the classification and identification of cephalopods in the stomachs of large marine predatory fish.
