Gonad maturity in female Chinese mitten crab Eriocheir sinensis from the southern Baltic Sea – the first description of ovigerous females and the embryo developmental stage

This paper describes for the first time the gonad maturity stage of Eriocheir sinensis females (carapace width 55.20–78.10 mm) collected in the autumns and winters of 2005–2012 in the Gulf of Gdańsk and Vistula Lagoon (southern Baltic Sea). Seventeen females had gonads in the penultimate stage, which indicates that spawning would shortly take place. Four other females had gonads in the last stage, which means they were already carrying eggs. These accounted, on average, for 17.9 ± 2.9% of female weight and were in the 3rd and 4th embryo developmental stage. The results show that the low salinity of southern Baltic Sea (≤ 7 PSU) permits mating and fertilization as well as embryo development in E. sinensis. It is still not clear, whether such a salinity level will enable hatching and the complete larval cycle.