Abstract: The present paper deals with the biology of the parasitic copepod Lernaea poly-morpha and the acquired immunity on the part of the hosts after its infeetion on silver carp and big-head. For the control of this disease, various compounds have been tested. The results of the experiments and observation are summarized as follows:1. The optimum water temperature of the egg-laying and hatehing of the anchor worm ranged between 20-25℃.2, The development of larvae including nauplius and copepodid stages depends very much on the temperature of the water. It requires about 14-16 days at 15-20℃ and 7 days at 26-31℃.3, During the cultivation of fingerlings from July to September and the water temperture ranges from 25-37℃, the average life span of the adult copepod is about 20 days.4, The anchor worm infected on the fish may be divided morphologically into three types which are easily discerned as "young worm", "adult worm" and "old worm".5, The fingerlings of silver carp and big-head which have been infeeted by a number of anchor worms may show definite acquired immunity after the parasites terminated their life and dropped off from the fish.6,For control of the larvae and adult of this parasite 25 chemicals have been tried. The results indicated that bathing in laboratory with a solution containing 12.5 ppm of potassium permanganate at water temperture of 24-30℃ is often effective to kill the adult without serious injury to the host. Although 0.8-0.5 ppm Dylox could not kill the adult, it is very effeetive in eliminating the larval copepods. It is suggested that the control of lernaeosis by adopting the spreading method is promising in the ease of rather large pond.7, The significance of the life span of Lernaca and the acquired immunity of the host after being infected has been discussed in relation to the control and treatment of the parasites.