Effect of salinity on the behavior and oxygen consumption of Mugil curema (Pisces, Mugilidae).

White mullet fingerlings (Mugil curema) occur together with freshwater species, of the Poeciliidae and Characidae, in a pond neighboring the beach at Pontal do Sul (Parana, Brasil). They tolerate changes in water quality during the year, brought about by the action of rains, waves and tides. When acclimating in the laboratory to various salinities, the highest survival rate for Mugil curema fingerlings (2.3 to 9.7 cm) is obtained at 8.5% salinity for temperatures between 13 and 30 degrees C. M. curema fingerlings do not survive in freshwater. The behavior of the individuals and of the group was related to the acclimation salinity in different temperature ranges. The most stressing condition, with highest oxygen consumption, was at 1.7% salinity; the equilibrium point between the internal and the external medium, with the lowest oxygen uptake, per gram fish, in one hour, was recorded at 8.5% salinity.

A technique for the determination of the available oxygen in living carp (Cyprinus carpio) muscle.

A polarographic method for the measurement of the available oxygen in the muscle of living carp by the use of a platinum microelectrode is proposed. The oxygen and the reference electrodes were assembled in a single insertion piece which was implanted in the muscle of a living carp maintained in a special experimental chamber. Curves for normal oxygen levels corresponding to air-saturated water, as well as to a carbogene-saturated water, were obtained. The method can be considered adequate for the measurement of tissue oxygen in living fishes.