Morphological variation in the Chinese clam Sinanodonta woodiana (Lea, 1834) in the heterogeneous conditions of the Konin heated lake system in central Poland

In the mid 1980s, the Chinese clam Sinanodonta woodiana (Lea, 1834) from SE. Asia was accidentally introduced in the Konin heated lake system (central Poland) from Hungary, along with fish stocking material. Currently, it inhabits abundantly the littoral zones of the five lakes that comprise the system, the initial cooling basin, and most of the associated intake and discharge canals. The considerable heterogeneity of its habitats in the system affects the morphological variation of its shells. The shell morphology, size, colour and growth rate are shaped by environmental factors, of which temperature, water flow intensity, and substrate type are the most important. The largest and heaviest specimens were found in the warmest habitats with the fastest water flow. Specimens with shells up to 160 mm long constituted most of the population, while in moderately heated areas the length was upto 125 mm, and in the coolest areas – 115 mm. The maximum individual weight was 900 g.