In support of aquaculture development and sustainable fisheries, survival, condition index, and stable isotope composition of the commercially important bivalve species Arca noae were investigated on individuals suspended in the water column at 2 distances from fish cages and those collected from natural populations. Significant differences were recorded in temperature and chlorophyll a with respect to season, and temperature and salinity values differed significantly with respect to sampling site. Mortality was greatest at the beginning of the experiment, probably as a result of the stress associated with collection of A. noae and the shell-marking process. The relatively small numbers of individuals that survived the experiment did not allow for a detailed statistical analysis of growth rates at the 3 study sites. Condition index showed a pronounced seasonal variation, with greater values recorded between April to July (CI, ∼24) and lesser values noted during November and December (CI, ∼20). Statistically significant intersite differences were detected. Samples collected from the control site in the Pašman Channel had lower condition index values than samples at other sites in 4 of 6 sampling months for which differences between sites were detected. Differences in stable carbon (δ¹³C_VPDB) and nitrogen (δ¹⁵N_air) isotope compositions were recorded with respect to tissue type and season, but no differences with respect to sampling site were noted. Results indicate that A. noae is highly sensitive to manipulation.