On March 5th, 2019, staff from Okinawa Churaumi Aquarium released one thousand captive bred Ryukyu-ayu fish into Nago City’s Genka River. The released fish will disperse from midstream to upstream, however the best possible way for their continued success is for them to increase the range of their habitat. This is achieved by improving movement within the streams around where the Ryukyu-ayu fish live, and it will also enlarge the range of other fish.
5km downstream from the source of the Genka River, a weir to control dangerous levels of soil erosion creates a sudden drop in river height. The weir would have prevented fish from traveling up the river, so a fish ladder was constructed to make it possible for the fish to swim freely. However, when this fish ladder becomes clogged by sediment it is less effective and loses its function. At the end of March, our staff volunteered to remove the sediment and driftwood that were causing the blockages and overflowing. After cleaning and removing the blockages, the fish ladder functions efficiently again.
Environmental conservation activities such as this are undertaken by the Churashima Research Center.

Before cleaning the fish ladder with blockages and overflowing. The effectiveness of the ladder is degraded.

We extracted the sediment and driftwood that caused the blockages.

After cleaning, the water flow improved, and the fish can swim upstream more easily.