The environmental factors affecting the end of spawning period in Bitterling, Acheilognathus melanogaster

Abstract

A. melanogaster were taken from an outdoor tank once a month from March 2013 to August 2014. From March to July both years, the GSI value stayed high and individuals with developed gonads were observed. However, in August both years, the GSI suddenly dropped, and individuals with regressed gonads were observed. These results indicate that the spawning season of A. melanogaster reared in outdoor tanks was from the end of March to the end of July. In order to investigate the factors which affected the end of the spawning season, in August both years, A. melanogaster were reared in different combinations of water temperatures and daylight lengths on May 10 and the summer solstice (June 21). The spawning of A. melanogaster was terminated for all daylight lengths at 28°C. However, the spawning continued in the case of the all daylight lengths at 20°C. The spawning was terminated under the conditions of 22°C 12L12D and 24°C 12L12D in the summer solstice. One of the main factors for the end of the spawning season seems to be the influence of high water temperature. However, it was revealed that short day treatment under the low water temperature conditions also helped end the spawning season.