Abstract
We examined the habitat characteristics of larval Cyprinidae (larvae: < 13 mm in total length [TL], juveniles: 13-30 mm TL) at a base flow (0.1 m3s-1) and under experimental flooding conditions (0.5 and 1.0 m3s-1 discharge) in two zones (BRZ: Backwater Research Zone, IFRZ: Inundation Frequency Research Zone) of experimental stream B in the Aqua Restoration Research Center in Gifu, Japan. Although the two zones appear as a straight channel, the environmental characteristics of the BRZ, which had three backwaters, were more diverse than those of the IFRZ. In the base flow study, most larvae and juveniles were captured near the shore of the two zones (low abundances) and in the backwater areas of the BRZ (high abundances), where water velocity was slower (2 cm/sec) and there were more areas with high cover (larvae: 56%, juvenile: 44%). However, fish were absent in areas of high cover (> 78%), with a high water velocity (6.6 cm/sec). Sites in the BRZ where fish were present were separated into two different habitat types: 1) shallow, slow moving water and fine substrate on the backwater borders; 2) deep water in the open areas of backwaters. This result suggests habitat segregation of cyprinid species at early growth stages. Larvae congregated in the backwater areas during the experimental floods, whereas juveniles did not differ significantly in the periods before and after flooding. These results suggest that diversity of floodplain morphology should be preserved to maintain larval habitats not only at the base flow level but also under various flow regimes.
