Our objective was to ascertain the relationship between the ultrasonic properties of fish and their composition Fish analogs with varying protein (15-25 wt%), lipid (0-25 wt%) and moisture (55-80 wt%) contents were prepared by mixing dried cod powder; sunflower oil and distilled water The temperature dependence of the ultrasonic velocity of fish analogs was measured from 5 to 35 degrees C. The ultrasonic velocity increased with solids-non-fat at all temperatures, but had a more complex dependence on far content. Around 15 degrees C the ultrasonic velocity was independent of fat, at lower temperatures it increased with fat, and at higher temperatures it decreased. Empirical equations were developed to relate the ultrasonic velocity to composition By measuring the ultrasonic properties of fatty tissue at at least two temperatures it should be possible to determine both the fat and solids-non-fat content. For non-fatty fish, the solids-non-fat content can be determined from a single measurement. Our results highlight the potential of ultrasonic velocity measurements to rapidly and nondestructively determine fish composition.