Abstract: Carassius auratus is everywhere the most common of our foodfishes;its ecological relationships are,however,very incompletely known.During the year 1956 to 1957,an ecological investigation was undertaken of about ten economic fishes in Lake Liang-Tze,but the present paper deals only with those results relating to Carassius auratus. The ordinary catch of Carassius in this Lake is composed of individuals from one to five years old,but the 2nd -year class fish are predominant,accounting for 80% of the total catch.Age deter- minations on this fish can be made easily by scale readings,the annulus formation being similar to that in the common carp (Cyprinus).The formation of the annulus appears also to take place during the breeding season,namely from May to July. The food-analysis of Carassius here confirms that it takes a very mixed diet,consisting of vegetable as well as animal material,though the vegetable debris from the bottom of the lake is the chief component throughout the year. Individuals of 9 cm.in length and one-year age-class are sexually mature.A sex-ratio of 4 females to one male is the normal for adults,but in young fishes the sex-frequencies are nearly equal.The adhesive eggs are laid in large quantities when the water temperature reaches 17℃.in early May.Larval fish are hatched 4(1/2)days after fertilization,and one month after hatching they have grown to resemble the adult in appearance.