In mussels gills and ciliary mechanisms associated with them serve to pump water and collect,
transport and sort food particles (Morton 1983). Food particles are entrapped in mucus strings and transferred to labial palps, which regulate entry of food into the mouth. The labial palps also help in rejection of excess material as pseudofaeces. Oxygen consumption is also closely linked with the pumping of water. Filtration and feeding in mussels have been extensively dealt with by Bayne (1976). Rajagopal (1991) has estimated the filtration rate in P. viridis as a function of mussel size, temperature, salinity and light –dark cycle. To estimate the amount of water filtered through the gills, he used the dye absorption technique (Coughlan 1969), which is based on absorption of neutral red by actively filtering mussels. The data show that filtration rate (expressed as volume of water filtered per mussel) increases with mussel size. Optimum filtration rates of P. viridis wereobserved at a temperature and salinity of 30 C and 30 –35&, respectively (Rajagopal 1991).The filtration rates were significantly higher in mussels kept in complete darkness, compared with those maintained in day light or light/dark conditions (Figure 11). It is generally observed (Rajagopal, unpublished data) that shadows falling on them disturb the feeding of P. viridis, probably as a defence mechanism against predators. Defence against predation could be the reason for higher filtration in darkness. Figure 12 shows oxygen consumption rates as a function of temperature. Optimum oxygen consumption occurred at 30 C, while at 40 C oxygen consumption declined to nil.