Effect of Thermal Acclimation and Sublethal Heat Shock Upon Ionic Regulation in the Goldfish,Carassius auratusL.

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Abstract
Goldfish acclimated to 20[degree] and 30[degree]C exhibited no significant differences in plasma Na level, tissue chloride, K and water content, and chloride space. Plasma chloride varied inversely and plasma K directly with temperature. Tissue Na levels tended to be slightly lower at the higher acclimation temperature. The shock response following abrupt transfer from 20[degree] to 30[degree]C was characterized by a complex sequence of changes in water-electrolyte balance. Following a lag period plasma chloride rose sharply, peaking some 48 hr after transfer, and subsequently declining. Plasma Na varied in substantially similar fashion. Changes in plasma Na/chloride ratio suggested the possible occurrence of a transient condition of alkalosis following thermal shock. Plasma K levels increased rapidly, and appeared to stabilize within 24 hr. By contrast, little variation in tissue levels of Na, K, and chloride was observed. Tissue water content, on the other hand, tended to increase steadily for several days after transfer. Changes in chloride space suggested that an increase in extracellular phase volume, in part at the expense of the cellular fluids, accompanied thermal shock. It is concluded that while thermal shock induces marked initial deivations in iono- and osmoregulatory ability the goldfish can, during the acclimatory process, carry out compensatory changes in regulatory activities which permit restoration of virtually the original ionic status. Possible mechanisms underlying the shock and acclimatory responses are discussed, and the bearing of studies of this general type upon the estimation of thermal acclimation rates is considered.