EFFECTS OF FOOD AND SILT ON FILTRATION, RESPIRATION AND CONDITION OF THE FRESH-WATER MUSSEL HYRIDELLA-MENZIESI (UNIONACEA, HYRIIDAE) - IMPLICATIONS FOR BIOACCUMULATION

The effect of exposure to different concentrations of food and suspend ed silt on filtration, respiration and condition were studied in the f reshwater mussel Hyridella menziesi. Using a milk solids-based food an d kaolin to simulate silt, mussels were maintained at different combin ations of food and silt concentrations for 3 weeks. Between treatments mean filtration rates ranged from 0.97-1.66 1 g(-1) h(-1), and respir ation from 0.50-1.35 mg O-2 g(-1) h(-1). Silt (non-volatile suspended solids up to 35 mg l(-1)) failed to have a significant effect on filtr ation rate or condition, but with increasing food levels (volatile sus pended solids up to 35 mg l(-1)) filtration rate was reduced, and cond ition was reduced at the lowest food concentration (<5 mg l(-1)). Resp iration showed a food x silt interaction between treatment blocks. Whe n food was low respiration increased with increasing silt concentratio ns, and when silt was low (<5 mg l(-1)) respiration increased with inc reasing food concentrations. The observed effects of food and silt on filtration, respiration and condition are discussed in terms of their potential for affecting contaminant bioaccumulation. In low-food situa tions (i.e., <5 mg l(-1)), if mussels are pumping large volumes of wat er, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates. Changes in metabolism with food concentration have implications for contaminant elimination, and changes in biochemical composition associated with ch anging condition could affect the tissue distribution and retention of contaminants.