RATES OF DEVELOPMENT IN EMBRYOS OF A CYPRINODONT FISH EXPOSED TO DIFFERENT TEMPERATURE– SALINITY–OXYGEN COMBINATIONS

Abstract

Eggs of the teleost fish, Cyprinodon macularius Baird and Girard 1853 (Cyprinodontidae) were transferred approximately 4 hours after oviposition into a variety of temperature–salinity–oxygen combinations: 48 different constant temperatures between 10° and 37 °C, eight salinities between distilled water and 85‰, and three concentrations of ambient dissolved oxygen approximating 70%, 100%, and 300% air saturation. All eggs had been produced by spawning groups of known environmental and biological history. Rates of embryonic development were determined as length of time between fertilization and hatching and as time to attainment of certain embryonic stages. Temperature curves of development are subject to considerable changes in the various levels of salinity and oxygen. In general, increase in salinity leads to progressive retardation of development, whereas increase in oxygen content produces progressive acceleration. Both retardation and acceleration become more and more accentuated as the temperature increases. Arresting and lethal temperatures, too, are a function of salinity and oxygen. Under normal atmospheric conditions and air saturation, the temperature–salinity combinations employed differ up to 65% in their content of dissolved oxygen due to different coefficients of absorption and saturation for oxygen in water. These differences are shown to be primarily responsible for the retarding effects observed in high salinities. The physiological effect of the salinity factor per se is rather limited. It may be more pronounced in eggs transferred immediately after oviposition. Combined and factor-specfic effects of the controlled trifactorial aspect of the environment are discussed in the light of pertinent literature.