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¹ University of Dubrovnik, Institute of Marine and Coastal Research, Damjana Jude 12, 20000 Dubrovnik, Croatia
² Ministry of Agriculture of Republic of Croatia, Fisheries Directorate, Marka Marojice 4, 20000 Dubrovnik, Croatia
³ Ruđer Bošković Institute, Center for Marine Research, Giordano Paliaga 5, 52210 Rovinj, Croatia DOI : 10.4194/1303-2712-v18_12_03 Viewed : 5116 - Downloaded : 2378 Bearded horse mussel and Noah`s ark shell are sometimes observed to live together in groups. Oxygen consumption, ammonia excretion and clearance rate were investigated on these species under laboratory conditions considering different size of individuals divided into three size groups (less than 25 mm; 25 to 50 mm and larger than 50 mm). Body size of both species significantly influenced oxygen consumption, ammonia excretion and clearance rate of the Noah`s ark shell. In both species, respiration and clearance rate decreased with body size while excretion rate increased with body size. For Noah`s ark shell groups of 25 to 50 mm and smaller than 25 mm, the atomic ratio between oxygen consumption and ammonium excretion i.e. O:N ratio was detected to be greater than 30. The same applies to a group of the bearded horse mussels smaller than 25 mm. Animals of both species larger than 50 mm have O:N ratio smaller than 30 indicating use of proteins as metabolic substrate, compared to use of lipids and carbohydrates in younger animals. Keywords : Oxygen consumption, ammonia excretion, clearance rate, O:N ratio, size, bearded horse mussel, Noah`s ark shell