Old and new immunomarkers to assess health status of clams (Tapes philippinarum) from the Lagoon of Venice.

The aim of the present study was to examine the health status of clams (Tapes philippinarum) from the Lagoon of Venice by means of immunomarkers. Bivalves were collected in June 2007 in 8 sites of the Lagoon characterised by differing contamination levels. Immunomarkers included total haemocyte count (THC), lysozyme-like activity in cell-free haemolymph (as measure of cell membrane stability), and vitellogenin (Vg)-like protein levels in both digestive gland and cell-free haemolymph. The results showed that clams sampled at Marghera and Fusina (highly polluted sites) had significantly reduced THC values with respect to those of animals from the other sites. Conversely, significantly increased THC was observed in clams from Valle di Brenta and Cà Roman, influenced by wastewater from agricultural areas and intense fishing and passage of ships, respectively. Significantly increased lysozyme-like activity was also recorded in cell-free haemolymph of clams collected at the most polluted sites (Campalto, Marghera, Cà Roman), suggesting that destabilisation of cell membranes occurred in haemocytes. Interestingly, altered Vg-like protein levels were observed in digestive gland and haemolymph of both male and female clams from contaminated sites. Vg induction is generally recognised as a biomarker of exposure to estrogenic compounds. However, in the light of recent findings concerning involvement of Vg in immune responses (Zhang et al. Fish Shellfish Immunol. 19: 93-95, 2005), application of Vg as potential immunomarker in future laboratory and field studies is suggested. On the basis of the immune responses analysed in the present study, we can conclude that the health status of T. philippinarum at contaminated sites is poor. However, influence of both exogenous (i.e., water temperature and salinity, food availability) and endogenous factors (i.e., reproductive cycle) on cell functional responses investigated have to be taken into proper account.