Seasonal changes of fishes ascending an irrigation ditch flowing into an inland-sea lake, Kitaura, eastern Japan

Abstract

Seasonal changes in upstream movements of fishes were examined in an irrigation ditch flowing into an inland-sea lake, Kitaura, Ibaraki Prefecture, eastern Japan, from April 2020 to March 2021. A total of 1,762 individuals representing 6 families and 12 species were collected using small fyke nets throughout the study period. The most abundant species were the gobiid Rhinogobius sp. OR(70.8% of the total number of individuals collected), the gobiid Gymnogobius urotaenia(22.5%), the cobitid Misgurnus anguillicaudatus(2.7%), the gobiid Tridentiger brevispinis(1.7%)and the cyprinid Gnathopogon elongatus elongatus(1.1%). Based on the body sizes, developmental stages and seasonal occurrence patterns of fishes sampled, it is highly likely that the irrigation ditch would be used as a place of temporary growth and spawning by several fishes including amphidromous gobiids.