Uncommon life history and winter spawning of common carp ( Cyprinus carpio ) in a natural thermal spring, under temperate climate

Common carp female generally matures at age 4–5 years old and spawns between April and July under the temperate climate. Contrary to a range of 0–28 °C of temperate freshwaters, the water temperature of Lake Hévíz (Hungary, Central Europe), the largest natural bathable thermal lake in the world, varies between 26 and 35 °C seasonally. The specific environmental conditions (continuously warm water and its individual chemical composition, special nutrient base, lack of natural lakeside spawning substrate compared to usual spawning grounds, continuous high human disturbance, etc.) suggest that the carp population here may also differ in reproductive characteristics from their counterparts in surrounding waters. Our findings suggest that the self-sustaining dwarf common carp population of Lake Hévíz matures 2 to 4 years earlier (at the age of one) and spawns 1 to 3 months before (between February and April, at 27–30 °C water temperature) than carp typically do in the temperate zone (16–20 °C). Successful winter spawning was verified by rearing larvae from the collected eggs and in situ induced propagation.