osmoregulation and oxygen consumption of the hololimnetic prawn, macrobrachium tuxtlaense at varying salinities (decapoda, palaemonidae)

Abstract

The osmoregulatory response and oxygen consumption rate of the strictly freshwater prawn, Macrobrachium tuxtlaense were measured under different salinity conditions. The goal of these experiments was to explore how the adaptive process to the freshwater environment has proceeded from a metabolic point of view in a hololimnetic species. Nine to 11 intermoult prawns were exposed to salinities of 0, 5, 10, 15, 20, 25, and 30 parts per thousand, respectively. Once oxygen consumption was measured, haemolymph osmolality was determined by sampling of 20 mu l aliquots. The results indicate that the oxygen consumption rate decreased significantly with increasing salinity. The respiration of prawns exposed to 5 parts per thousand salinity was 56% higher than the rate of those exposed to 20 and 25 parts per thousand. The prawns behaved as strong hyperregulators in low salinity

at higher salinities, the haemolymph osmolality showed a sharp increase, although it remained hyperosmotic to the medium

the isosmotic point was reached at 700 mOsm. Based on our results, M. tuxilaense in general shows a pattern similar to that of other hololimnetic species, but with some unique aspects, such as a high isosmotic point and an inability to survive at salinities above 28 parts per thousand. This suggests an advanced degree of adaptation to the freshwater environment.