A comparative study was carried out on the functional feeding behaviour of the infaunal Manila clam, Ruditapes philippinarum, and the epifaunal Asian date mussel, Musculista senhousia, inhabiting the Sacca di Goro lagoon, in response to changing temperature and variable quantity of food. The rates of clearance, ingestion, absorption, respiration, and energy budget (scope for growth, SFG) were measured and compared. The two non-indigenous species show a similar trend for all parameters measured in the two seasons considered (late winter and summer). SFG followed a clear seasonal trend, reaching higher values in the warmer period (July) for M. senhousia and in the cooler period (March) for R. philippinarum. Probably, this seasonal divergence was a consequence of the two species' different reproductive cycles.