Abstract
Recently, some reports described that the population of fishes that inhabit in the water zone of paddy field areas has decreased because of disconnecting watercourse network by the farmland consolidation project. As one of the engineering technologies to reconnect watercourse network, development of small-scale fishways installed atoutlet of the paddy field has been conducted. In such case, it is necessary to consider swimming performance of smallfishes todetermine installation dimension. In this study, therefore, swimming ability of loach Misguruns anguillicaudatus and crucian carp Carassius sp. was evaluated by a pipeline equipment. The results obtained were as follows;1) Since to measure so-called “rush speed” and “cruising speed” was considerably difficult, the swimming ability wasexamined under three categorized swimming forms, i.e. ascending, non-ascending and descending, 2) Loaches with 5 cm standard body length, loaches with 7 cm standard body length and crucian carp with 4-6 cm standard body length widely carried out ascending migration against the 50 and 70 cm·s-1 flow velocity, and 3) An obtained relational expression, the ratio of flow velocity to the standard body length of fish that ascend against flow with success ratio of 40%, were 15.5, 12.3, and 13.7 in the cases of Loaches with 5 cm standard body length, loaches with 7 cm standard body length and crucian carp with 4-6 cm standard body length respectively.
