Factors Involved in the Production of Annual Zones on the Scales of the Rainbow Trout (<i>Salmo Irideus</i>). II

ABSTRACT Rainbow trout fed uniformly does not exhibit any periodic zones on its scales whether the temperature is normal or high or low. At both high and low temperatures (17° C. and 4° C.) fish fed abundantly show on their scales a peripheral band of comparatively broad rings, and fish starved show a peripheral band of narrow rings. Bands of broad and narrow rings, resembling the so-called “annual zones,” could be produced on the scales by altering the food supplies of the fish irrespective of the temperature of the medium. Variations in temperature have no direct effect on the production of the periodic rings on the fish scales.