Importance of a Reed Community as a Nursery for Nigorobuna, Carassius auratus grandoculis

Abstract

Nigorobuna is an endemic fish species in Lake Biwa and is useful in the production of “funazushi”, a traditional fermented food in Shiga Prefecture. The importance of a reed community has been confirmed as a nursery area for this species.Nearer the shore within a reed community, there is abundant zooplankton, but dissolved oxygen is in such low concentration that fishes don't generally live there. However, it has been observed that nigorobuna larvae gather there to develop. On the other hand, it has been confirmed that when the nigorobuna have reached the juvenile stage, as their cruising speed increases, they depart the reed community.The nigorobuna juveniles with otoliths dyed in 3 different patterns by ALC were released respectively to the reed community, the sandy beach and more centrally around the northeast region of Lake Biwa. Nigorobuna specimens were gathered by small trawlnets from the northern basin 6 months latter. Then, their otoliths were checked, and a ratio of the survival rates of the fish released to each area was analyzed. This showed that the fish released outside the reed community, hardly survived, even though they had reached the juvenile stage.These results suggest an importance of a reed community as a place to rear infant nigorobuna.