Research

Research Topics

Example of research topics

For Comprehensive Ecosystem Management

Recently, there is increasing demand for approaches to provide comprehensive ecosystem management that considers interspecific and individual level interactions that shift away from conventional fishery management based on a single-species. In aquatic ecosystems, typical energy flow is based on a trophic pathway in which larger individuals eat smaller individuals. Therefore, the body size of fish is a key factor to understand individual life histories and ecosystem dynamics. However the size of organisms in aquatic ecosystems varies by several orders of magnitude. For example, the mass of the smallest fish is approximately 2 milligrams, while blue whales can grow up to 100 tons, creating a size difference of 11 orders of magnitude. Even at the ontogenetic level, a bluefin tuna (Thynnus thynnus) changes its body mass in its lifetime from 0.2 mg at spawning to 300 kg as a fully matured individual, creating a size difference of 9 orders of magnitude. Based on such differences, we focus on the body sizes of organisms and aim to understand the structure and dynamics of aquatic ecosystems at the individual, population, community, and ecosystem levels based on allometric “size scaling” theory to ensure the sustainable use of aquatic ecosystems and resources.

Fish Migration and Life History Strategies Revealed by Otolith Analyses

The life history of diadromous fishes can be estimated based on their otolith microstructure and microchemistry, which show their migration patterns and life history strategies. Otolith concentric rings are formed according to the individual’s age and growth. Special otolith microstructures are also formed and trace elements are taken into the otolith during specific life history events such as hatching, first feeding, metamorphosis, settlement, and migration etc. These otolith microstructures are observed using a scanning electron microscope (SEM), and otolith elemental compositions and isotopes are measured using an electron probe micro analyzer (EPMA) or an inductively coupled plasma mass spectrometer (ICP-MS).

Migratory Patterns and Evolution of Catadromous Eels

Anguillid eels are known as typical catadromous fish. Most temperate eels such as European eels, American eels, and Japanese eels migrate long distances of up to thousands kilometers between their spawning areas and growth habitats. While, there are many sympatric anguillid eel species in tropical regions, their migration scales are much smaller than temperate eels. How and why the small-scale migrations of tropical eels evolved from entirely marine species, and how did these migrations evolve into the large-scale migrations of temperate eels, are important questions to explore. To reveal the migration patterns of anguillid eels and their evolution, we have been conducting research cruises in the Indo-Pacific region, and have analyzed the morphological characters, distribution patterns, and early life histories of eel larvae, which are called “leptocephali”.