Abstract
Collection surveys were conducted to investigate the feeding habits of amphidromous sculpin Cottus pollux middle-egg type in the Sendai River system in Tottori Prefecture. At the sampling station, located approximately 13 km upstream from the river mouth, newly recruited individuals with standard lengths of around 30 mm occurred in June. The stomach contents index (SCI) of C. pollux middle-egg type showed a decreasing trend from summer to autumn. Particularly, the low percentage of individuals with stomach contents in autumn suggests a potential shortage of food resources. Analysis of the index of relative importance of food items (IRI) indicated that the C. pollux middle-egg type primarily relied on aquatic insects of Trichoptera and Ephemeroptera. The increase in the percentage of IRI for Diptera in autumn, when food resources were scarce for the C. pollux middle-egg type, suggests that Diptera could compensate for food shortages. Although C. pollux middle-egg type is listed as an endangered species, the lower reaches of the Sendai River system are considered valuable habitat for this species due to the presence of suitable environmental conditions.
https://ror.org/0575dme84 
