Efficiency of passive integrated transponder tags on juveniles of far eastern catfish, Silurus asotus for studying ecology by applying in a small river.

Abstract

The ecology of far eastern catfish Silurus asotus is poorly known particularly in the early life stage. Passive integrated transponder（PIT）tags have been a successful tool to evaluate the ecology of endangered fishes such as a far eastern catfish with relatively large bodies（TL＞ca. 20 cm）. However, there is no study applying the PIT technique to small individuals of far eastern catfish. Here I provide a case study applying 12-mm PIT tags to the juvenile of far eastern catfish. To evaluate the effects of the 12-mm PIT tags implantation on juvenile far eastern catfish, I compare growth and survival among three experimental groups; control, surgery with no tag, and surgery with tag. After the 24 days observation, neither expulsion of the PIT tag, nor death of fish is found in every tagged individual, as well as no significant difference in the growth among the three experimental groups. Subsequently, I explore the efficiency of the PIT technique by tracking and locating tagged individuals in a small river named Yagawa, Tochigi prefecture, central Japan. A total of 21 far eastern catfishes, which were caught in the Yagawa river, were released after being tagged by the 12-mm PIT tags in the abdomens. A portable waterproof antenna is used to locate the position of tagged fish in the study section. Although the detectable dis- tance in the field is no more than 50 cm, 12 individuals were successfully traced with the PIT signals. The longest trace record is up to 300 days after release accomplished by two individuals. All these results indicate that the PIT implantation technique and the tracking survey in the field are effective to collecting the ecological information of far eastern catfish including juveniles.