Abstract
This study examined the growth of aquatic animals in the canal system constituting the main, lateral, and farm drains in a consolidated paddy field, with emphasis on canal structure and year-round water flow in the canals. A field survey at six sites, which involved three different canal levels, was carried out in Chikusei, Ibaraki Prefecture, Japan (36゜21'N, 139゜59'E). Sampling was conducted at monthly intervals from April 2001 to March 2002. Of the freshwater fish, young-of-the-year (YOY) Zacco platypus appeared in September, while YOY Misgurnus anguillicaudatus appeared in May. Last instars of the damselfly Calopteryx atrata were collected only in June, suggesting emergence about this time, while those of the dragonfly Orthetrum albistylum speciosum were collected in May and July, suggesting a longer duration of emergence. Since populations of the four species decreased during the non-irrigation season when the water level was low, I propose that a marsh be developed as a wintering site in the lower reaches of the canal system in consolidated paddy fields.
