Feeding habits of Diaphus watasei juvenile fish in offshore waters of southwestern Taiwan

• Main Authors: Huang, Ting-Hsuan, 黃鼎軒
• Other Authors: Lee, Ming-An
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/dthbya

碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 107 === The fish of the genus Diaphus is involved in the transfer of zooplankton to the higher trophic levels in the marine food web. The wide range of characteristics and a rich biomass make its presence very often in the stomach of the top oceanic predators. In this study, we focus on the feeding habit of Diaphus watasei was conducted from November 2017 to May 2018 and November 2018 to February 2019. Samples were collected from the south-western part of Taiwan captured by sakura shrimp trawl. Stomach content index (SCI), relative importance index (IRI), and costello graphical method were used to analyze the prey composition and feeding strategy, and then the differences in body length and sex were investigated using Shannon-Wiener diversity index, diet breadth (Ba) and overlap (CH). A further study on the stable isotope analysis described the trophic position of the species. A total of 532 samples were collected for analysis during the study period including 187 male and 345 female samples with a length range of 57.65mm to 115.35mm. The Stomach Content Index (SCI) showed the decreased feeding intensity month by month with shrimp (Sergestidae spp.) and lantern fish (Benthosema pterotum) as main feeding items in each body length. The prey composition of the diet showed a high overlapping between the sexes, length range and study period. The possible reason for this high overlapping may be associated with the short length range or stable environment. The specific feeding strategy to shrimp can be defined using the “Costello graphic method”. Analysis of stable isotope showed a tendency of slightly increasing of the nitrogen isotope with increased body length but no significant relationship from the statistical analysis indicated no change in the composition of the prey organism with body length, thus showed similar stable isotopes. The average trophic position of 3.1 indicated that the Diaphus watasei in the southwestern part of Taiwan connects the secondary producer and higher trophic level. In summary, the stomach content analysis (SCA) and stable isotope analyses (SIA) shows a better understanding about the interactions between the organisms in the offshore waters of southwestern Taiwan ecosystem and the ecology of the Diaphus watasei.