SOME ASPECTS OF OSMOREGULATION IN TWO SPECIES OF SPHAEROMID ISOPOD CRUSTACEA

¹ Department of Zoology, University of California, Davis, California

1. Osmoregulatory requirements were analyzed and compared in Menzies' two subspecies of Gnorimosphaeroma oregonensis (G. o. oregonensis and G. o. lutea) and Sphaeroma pentodon Richardson.

2. The mechanism of osmoregulation was studied by measuring changes in the total osmotic concentration of the body fluid after three to 48 hours' exposure to various experimental salinities ranging from fresh water to 125 per cent sea water. Changes were also measured in the field during a partial tidal cycle. The principal findings and conclusions are as follows:

a.) The body fluids of the experimental animals became either diluted or concentrated in the experimental salinities. Generally, in more dilute media (50% sea water or less), the body fluids were maintained hypertonic to the medium, while in more concentrated media (75 to 125% sea water), they were usually maintained hypotonic to the medium.

b.) The lack of weight changes in experimental salinities in experiments conducted at 16° C. indicates that dilution and concentration of the body fluid at normal temperatures are caused primarily by salt movement.

c.) Pronounced weight changes that occurred in experiments conducted at 5° C. suggest that the normal water component of the body fluid is actively maintained and that low temperature interferes with this active maintenance, which normally permits excess water to leave the body in diluted media and to enter in more concentrated salinities. However, the fact that the degree of concentration and dilution of the body fluids at the low temperature could not be explained solely on the basis of water movement suggests concurrent salt gains or losses.

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