Chloride and osmotic regulation of the grass shrimp Palaemonetes pugio exposed to polychlorinated biphenyls (PCBs)

Abstract

Grass shrimp Palaemonetes pugio were capable of hypo- and hyperosmotic regulation of body fluids. Hemolymph chloride and osmotic concentrations were maintained at relatively stable levels over a wide salinity (S) range. Following an abrupt transfer from intermediate (14 - 17 o/oo S) to high (31 - 35 o/oo S) and low (1-2 o/oo S) salinities, hemolymph chloride levels exhibited initial overshoot and undershoot, respectively, of new steady-state levels. Osmotic concentrations exhibited initial undershoot at low but not overshoot at high salinity. Chloride space in salinity-acclimated shrimp was relatively stable at salinities from 1 - 35 o/oo S. Changes in chloride space following salinity transfer paralleled those of hemolymph chloride levels and were discussed in light of alterations in intracellular sodium concentrations reported earlier. Rate constants for chloride turnover indicated independent exchanges of sodium and chloride ions. Water turnover measurements showed that permeability of P. pugio was greatest at the isosmotic salinity (17 o/oo S) and reduced at salinities which were associated with active osmoregulation. Glycine was the most abundant free amino acid (FAA) in shrimp abdominal muscle, accounting for over 50% of the total pool. Arginine, alanine, proline, taurine and serine were also present at relatively high concentrations. Following transfer from 17 to 2 and 32 o/oo S, new steady-state levels of total FAA were observed at 72 h. Total FAA and the sum of glycine, alanine and proline exhibited a positive correlation with salinity. Exposure to Aroclor 1254 did not seriously alter hemolymph chloride and osmotic concentrations, chloride space, chloride exchange kinetics or total FAA levels in adult shrimp. Disruption of hemolymph chloride regulation in juvenile shrimp was associated with large mortalities not observed in adults..