It has been reported that pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, appear in small and large size groups during spawning despite being an annual fish. It is hypothesized that pond smelt have a bimodal life history, anadromous for large size groups and resident in the lake for small size groups. We calculated the body length and growth rate of the small and large size groups through the use of daily otolith increments and compared growth parameters between groups. In addition, the growth processes of resident fish in Lake Ogawara and anadromous fish in the adjacent sea were examined and compared with small and large size groups, respectively. We found that the two size groups diverged after 40-50 days from hatching with significant size groups present after 50 days. Through otolith increment analysis the growth processes of the small and large size groups were correlated with resident and anadromous forms respectively. These results revealed the utility of otolith increment analyses to clarify population structure of this species.
- Life history