Phenology of three coexisting annual fish species: seasonal patterns in hatching dates

Annual fish are specialized freshwater fishes that are adapted to live in seasonal freshwater pools. Their life cycle is tightly adapted to seasonally predictable aquatic and desiccated phases in their habitat. We used daily increments in otoliths to test the hypothesis of the direct association between seasonal rains and hatching dates of three coexisting Austrolebias species across 14 temporary pools in the Uruguayan pampa. Hatching was relatively synchronous within and between species across a small but topographically diverse region. Hatching occurred over 1 month in midautumn and peaked between 15 and 20 April 2015. The prediction of earlier hatching of a large predatory annual fish species was not confirmed. Unexpectedly, an unusual desiccation event in the middle of the winter growing season (May–July) affected many pools. Some pools re-filled after extensive precipitation in August, followed by the hatching of a new cohort in some (but not all) of those pools. The first cohort survived throughout the year (until late spring) in the pools that did not desiccate. Our study demonstrates how annual fish can cope with unexpected seasonal rainfall patterns that may be a consequence of current climate change.