OSMOREGULATORY CAPACITIES OF TWO CARIDEAN SHRIMPS, SYNCARIS PACIFICA (ATYIDAE) AND PALAEMON MACRODACTYLUS (PALAEMONIDAE)

¹ Department of Zoology, University of California, Berkeley, California 94720, and Bodega Marine Laboratory, University of Califorina, Bodega Bay, California 94923

1. Syncaris pacifica (Atyidae) is restricted to fresh water, like most members of the family. The striking osmotic adaptation in this shrimp is elaboration of urine markedly hypo-osmotic to blood. In fresh water, the following average body fluid concentrations were found: blood,_i 0.73° C. (F. P. depression), chloride, 185 meq./L.; urine, _i 0.18° C. This is the first report of dilute urine in any decapod other than crayfishes.

2. Palaemon macrodactylus (Palaemonidae) is a strong regulator over the range 2-150% SW, and inhabits a wide range of salinities in the San Francisco Bay estuarine system. Blood and urine are isosmotic throughout the tested range of salinities. Hyper-regulation occurs below 60% SW, and hypo-regulation in higher salinities. Between 20% and 100% SW, _i increases only from 1.19° to 1.65° C., as environmental salt concentration increases from ₀ 0.50° to 2.08° C.