Osmoregulasi Kijing Air Tawar (Velesunio ambiguus Phillipi)

Abstract

Tbe salinity tolerance and osmotk regulation of tbe freshwater mussel Velesunio iunbiguus Phillipi bas been studied In response to osmotk st-. This specks of organism could t o l e ~ tsea linity between 0 and 5 ppt (2 and 165 mOsla/kg) so tbat it could be coasidered as a stenobaline fresbwater animal The mllssel regulated its baemolympb mmotic pressure over tbe salinity ranges 0-3 ppt (2-93 yOsaJkg) and it conformed to salinity among 3 and 5 ppt (93-165 mOsm/kg). For Na', it was found to be a regulator below ambient ~ a o'f 23.51 mM and a conformer above this concentration. For K+, this bivalve behaved as a regulator. Haemolymph osmotk pressure, the concenhtioe of Na' .ad Kt in tbe haemolymph, and tbe intracellular free amino nckb (IFAA) of fed tissues incre.sed as the ambient salinity (osmohlity) increases from 0 ppt (2 m O sto ~5 pp t (165 mOsm/kg). The increase In extracellrlu fluid (haemdympb) pressure and ionic concentratbn, as well as the total IFAA h slower than t k decrease of the same parameters when the mussels were exposed to salinity stress. It appeared tbat the mussel Vclemnio umbiguus employed its sbelk to buffer against abrupt byperosmotic stress.