PhD Environmental Science, Hokkaido University (Japan), 2024
MSc Environmental Science, Hokkaido University (Japan), 2021
BSc Fisheries, Hokkaido University (Japan), 2019
Email: ryotahase344922@gmail.com
Evolutionary and Ecological Parasitology Research Group
Research interests
- Ecology and Taxonomy of parasitic copepods
- Ecology of freshwater fish (mainly salmonids)
- Association between fish body condition and parasite infections
- Parasite community assembly
I’m a parasite ecologist mainly working on host-parasite relationships between salmonid fishes and parasitic copepods of the genus Salmincola, which infects the mouth and gill cavities of their hosts. My focus has been on how copepod infections alter host behaviour, body condition, and survival. Then, my interest shifted to parasite-parasite interactions within individual hosts and their consequences on host ecology. Here in Dunedin, I’m currently working on whether priority effects contribute to creating trematode communities in amphipod hosts and their consequences for host fitness and ecosystem functioning.
Current postdoctoral project
Priority effects in parasite community assembly and its consequences on amphipod host fitness and ecosystem functioning
(JSPS Overseas Research Fellow; Japanese Society of Proportion of Science)
Publications
Hasegawa, R., & Poulin, R. (2025). Effect of parasite infections on fish body condition: A systematic review and meta-analysis. International Journal for Parasitology. Advance online publication. doi: 10.1016/j.ijpara.2025.03.002 Journal - Research Article
Hasegawa, R., & Poulin, R. (2025). Cause or consequence? Exploring authors' interpretations of correlations between fish body condition and parasite infection. Journal of Fish Biology. Advance online publication. doi: 10.1111/jfb.70048 Journal - Research Other
Hasegawa, R., Hasegawa, Y., Yamashita, Y., Inoshita, M., & Koizumi, I. (2025). Highly threatened status for the relict populations of ectoparasitic copepod Salmincola californiensis in Japan. Aquatic Conservation, 35, e70073. doi: 10.1002/aqc.70073 Journal - Research Article
Hasegawa, R., Otsuki, Y., Uemura, Y., Furusawa, C., Naka, M., Kanno, Y., & Koizumi, I. (2025). Positive feedback between parasite infection and poor host body condition reduces host survival in the wild. Functional Ecology. Advance online publication. doi: 10.1111/1365-2435.14742 Journal - Research Article
Hasegawa, R., Murakami, L., Aruga, N., Sato, N., Nakamura, S., & Koizumi, I. (2024). Host specificity of the parasitic copepod Salmincola markewitschi in an aquarium [Short communication]. Fish Pathology, 59(4), 139-142. doi: 10.3147/jsfp.59.139 Journal - Research Other