ONTOGENY OF OSMOREGULATION AND SALINITY TOLERANCE IN CANCER-IRRORATUS - ELEMENTS OF COMPARISON WITH C-BOREALIS (CRUSTACEA, DECAPODA)

Osmoregulation and salinity tolerance were studied in zoeae, megalopae, first crab stage (osmoregulation only), and adults of Cancer irroratus, and in zoeae and adults of C. borealis. In C. irroratus, salinity tolerance was moderate in zoeae, decreased in late zoeae 5, was at a minimum in megalopae, and increased in adults. The lower and upper lethal salinities for 50% of the animals (48 h LS 50) at 15-degrees-C were about 13-17 parts per thousand/42-50 parts per thousand in zoeae, 24 parts per thousand/37 parts per thousand in megalopae, and 8.5 parts per thousand/65 parts per thousand in adults. In C. borealis, the corresponding values of LS 50s were 16-20 parts per thousand/46-50 parts per thousand in zoeae and 12 parts per thousand/65 parts per thousand in adults. In both species, zoeae were hyper-osmoconformers; adults were isosmotic in high salinities and slightly hyper-regulators in low salinities. In C. irroratus, the change from larval to adult type of regulation occurred from megalopa (hyper-osmoconformer) to first crab stage (hyper-regulator in dilute media), i.e., after the completion of metamorphosis. Osmoregulation and salinity tolerance appear correlated and are modified at metamorphosis. These results are discussed with an emphasis on the effects of metamorphosis on osmoregulation of developing decapods.