Histological studies on the zebra mussel Dreissena polymorpha reproduction from a DDT contaminated area in Lake Maggiore (N. Italy)

Histological techniques were used to monitor Dreissena polymorpha reproductive biology during 2001 in Lake Maggiore (N. Italy). Considering the DDT pollution which occurred during the mid 1990s in this lake and the high contamination level registered in 2001, we focused on the course of spawning events in zebra mussels and possible modified reproductive behavior induced by this pollution. Specimens were collected from the lake at Baveno as the polluted station, and at Villa Taranto as the control site. At Villa Taranto, morphological analyses of gonadal changes showed a gamete developing and maturing period until April, spawning phases from May to August, the restart of gametogenesis in females and an inactive period in males, immediately after the end of spawnings. This pattern was perturbed at Baveno where the mussels showed a delay in oocyte maturation with a significant percentage of specimens showing oocyte degeneration. Moreover, the onset of gamete release seemed to shift from May to July in the males at Baveno. Our findings agreed with the well recognized endocrine disrupting properties of DDT, even though the physiological mechanisms involved must be studied further.