As for creatures, especially fish, in the water system, "Washu Yoshino-gun Gunzanki" written by Tomoari MINAMOTO in the Kowa era (the later Edo period) lists five kinds of fish including Japanese char (locally called kirikuchi), ayu (sweetfish), red spotted masu trout (landlocked masu salmon) and eel; after that, plenty of investigations and studies has been conducted on freshwater fish in Totsu-kawa River and its branches.
水系に産する生物、特に魚類については、源伴存の『和州吉野郡群山記』（弘化年間）がイワナ（地方名キリクチ）、アユ、アマゴ（ヤマメ）、ウナギの5種を記載して以来、十津川とその支流に見られる淡水魚について、多くの調査研究が行われてきた。