TIME-TEMPERATURE RELATIONS IN THE INCUBATION OF THE WHITEFISH, COREGONUS CLUPEAFORMIS (MITCHILL)

1. Whitefish eggs incubated in aerated lake water at controlled tempera tures of 0 degrees , 0.5 degrees , 2 degrees , 4 degrees , 6 degrees , 8 degrees , 10 degrees , and 12 degrees C., failed to hatch at either 0 degrees or 12 degrees C. 0.6 per cent hatched alive at 10 degrees C., 72.67 per cent hatched alive at 0.5 degrees C., and an intermediate proportion hatched at intermediate temperatures. 2. The percentage of abnormal embryos which developed to the hatching stage varied directly with temperature between 4 degrees and 12 degrees , all embryos being abnormal at 12 degrees C.; but none were abnormal at either 0.5 degrees , or 2 degrees C. Normal development predominated from 0.5 to 6 degrees C. The highest proportion of embryos to hatch alive was 72.67 per cent at 0.5 degrees C., which is, hence, the optimum temperature. 3. Total incubation time ranged from 29.6 days at 10 degrees C. to 141 days at 0.5 degrees C. 4. The time (T) required to attain any given stage of development is expressed in equations See PDF for Equation where temperature, t, is a negative exponent of the constant, A, whose value differs above or below 6 degrees C., a critical temperature. Values of A above 6 degrees fluctuate about 1.13; those of A below 6 degrees fluctuate about 1.19 as a mean. 5. Applying Arrhenius' equation micro values for the total incubation period are 27,500 below 6 degrees and 27,100 above it. 6. The relative magnitude of A values of the exponential equation and micro values of Arrhenius' equation show corresponding changes from one developmental period to another. 7. When plotted, thermal increments show cyclic variations, with maxima during periods of cleavage and of organogenesis. These may indicate the interaction of two separate sets of embryonic processes, which give a maximal response to temperature differences during these two separate periods. 8. Above 6 degrees , micro values during the hatching process are distinct from those of developmental stages and are regarded as being due to the action of hatching enzymes.