Associate professor


itsuro (at)


Field-based ecology

My main research interest is metapopulation ecology of stream Dolly Varden charr, a salmonid fish. I’ve been monitoring more than 100 local habitats (tributary streams) over 15 years (review in Koizumi 2011). I’m interested in how dispersal affects population dynamics, genetic structure and evolution of life history traits. I also aim to develop research frameworks applicable to other study systems (e.g. Koizumi et al. 2006; Koizumi et al. 2008). Because I was a fisherman (meaning I love fishes!) I’ve studied Dolly Varden from many different viewpoints, such as morphology, behavior and genetics. This provided me with broad concepts and methods for general ecological research, which are applicable to other animals. You can see this from the broad research topics of my students. These topics may appear independent but actually relate to one another. I hope such diversity will produce some novel research questions and theories.


Post Doctoral fellow

 Suvi Sallinen (JSPS post doctoral fellow)



Ecology and evolution of parasite communities

My main research interests are the ecological and evolutionary processes that govern multiparasite infections on different scales of ecological organization (within-host, within population, among populations). Here in Hokkaido University, I am using next-generation sequencing and joint species distribution modelling to investigate how host population genetic diversity, habitat type (urban/natural), and parasite communities are linked in two rodent species. In the Koizumi-lab, I am especially enjoying the diversity of study systems and topics, and focusing on the animal kingdom after previously working with plant viruses and fungal pathogens.

Doctor course

Noriyasu Suzuki

PhD student (3++ year)
noriyasu_s_suzuki (at)

Conservation ecology of Golden Venus chub

I am studying the ecology of Golden Venus chub in Shiga prefecture, which is far from Hokkaido. I’d like to attract people’s concern to the tiny, beautiful endangered fish, which should contribute to the conservation.


Yuuki Shimamoto

PhD student (3+ year)

The effects of domestication on fishes: focusing on brain structure & cognitive abilities

Organisms have the ability to obtain information from the outside world and respond appropriately. The brain plays an important role in recognizing the environment surrounding themselves and processing the information obtained from it. The shape of the brain is very diversified, not only among different taxonomic groups, but also within the same groups, corresponding to the environment where they live.
So how are the brains of domesticated fishes living in very different environments from nature changing compared to fishes living in nature? I would like to conduct research on various fish species that are domesticated not only in Hokkaido but also nationwide, focusing on the form and cognitive ability of the brain.


 Ryota Hasegawa (JSPS research fellow DC2)(personal website)

Doctor student (2nd year)

Interactions between parasitic copepods and salmonids

I was studying at the faculty of fisheries when I was an undergraduate student in Hokkaido University, Hakodate. But after bachelor, my passion for “Parasite” brought me to Sapporo again! I’m interested in the interaction between parasitic copepods and their hosts, freshwater salmonids. Furthermore, I’m focusing on the effects of habitat fragmentation by damming. If my research will be useful for their conservation or management, that will be awesome !


Masahiro Naka

Doctor student (2nd year)

Fish and parasite community

I like salmonids and also have interests in parasites, so I’d like to reveal the hidden interactions among them. I’m looking forward to
studying in Hokkaido especially doing fieldwork, and of course fishing.

P.S. First annual census of Dolly Varden made me exhausted, but the nature and dollies are very beautiful!!!


Chiharu Furusawa (JSPS research fellow DC2)(personal website)

Doctor student (2nd year)


Fish sleeping

I am interested in behavioral ecology, which considers animal behavior from the perspective of adaptive significance. My pastime is underwater observations, snorkeling day and night, in the river, or in the sea. I recently bought a dry suit, so I’m looking forward to winter diving in Hokkaido! In this Lab I will study fish sleep behavior, which I often encounter during snorkeling. The more I do, the more I feel fun! This is my motto :)


Yohsuke Uemura (JSPS research fellow DC1)(personal website)

Doctor student (1st year) (at)


Predicting the distribution and population dynamics of competing salmonids under climate change

Hello, I’m Yosuke. It’s been more than 20 years since I love fish. I’ve kept a good relationship with fish :)
I was just a “fish lover” in the begining, but with various experiences, I have many questions like “how fishes are interacting with each other?” or “how are fishes interacting with people, society, or the world?” and ended up coming to this lab. Another big reason coming to this lab was to do “Power Ecology” in the northern widlderness land, which is incomparable to my hometown Shikoku. By keeping myself in the nature, “I want to know how much I can try!” I was moving my feet north to north … (and into the deep forests).
Here, Koizumi Lab is focusing on field-based ecology, and I would like to do this for salmon fishes !
Ah … my hobby is drawing pcitures and human watching!
thank you!

Tomoaki Konno (Personal website)

Doctor student (1st year)


Interactions, co-evolution, and co-phylogeography of crayfishes and their eco-symbionts

Hi, I’m Konno. I love nature and all living creatures. I came to the graduate school because my desire to know nature became stronger as I learned more. My major organisms here are crayfish and their ectosymbionts, Branchiobdellida, so-called “crayfish worms”. I will also study the Ostracoda attaching to invasive crayfishes, which I’ve been studying since undergraduate course. The alien crayfishes are not good if escape to nature, so when I catch them and I’ll cook them properly (they are tasty!!!). I also investigate the phenotypic plasticity of the forces of earwigs. My dream is to clarify the history of crayfish, branchiobdellida, and ostracoda in their co-evolutionary history of 200 million years. My pastime is to take a picture.

Master course

Yasuhiko Otsuki

Master student (2nd year)

Interspecific competition between Dolly Varden and white-spotted charr

Hello, I’m Yasu Otsuki. I lived in Nagano prefecture during undergraduate. There are a lot of mountains in Nagano, and I climbed many of them. I’m interested in ecology of freshwater fish, especially salmonid fishes. In Koizumi lab, I will do many fieldworks and I want to learn a lot from wild animals in not only Hokkaido but around the world.






Past member