ウナギの隠れ場における適切な底質粒径の提案

抄録

It is reported that eels (Anguilla japonica) dig holes in order to form their nests, which is crucial for their survival. Some of their nests are in an area with vegetation or a deposited gravel space. However, little is known about the ideal gravel diameter for eels to dive as well as the process of forming nests in each eels’ grow stage. In this study, an investigation on behavioral characteristics of eels was conducted according to change in the gravel diameter on a pool bed and the eels’ body length. The results showed that eels have a tendency to swim near the sidewall of the pool. In addition, it was observed that eels insert their heads into the gravel and shake their bodies while diving into the gravel. It was also found that eels of 200mm in body length tend to avoid diving into any gravel in the range of 2-5mm diameter. However, they preferably dive into the gravel at 20mm diameter. Lastly, it was found that eels of over 300mm in body length dive into the gravel regardless of the gravel diameter.