Abstract: The development of PMA in adult and juvenile of Silurus asotus was investigated by peritoneally injecting with different dosages of bovine serum albumin(BSA)or Indian ink to stimulate macrophage(mφ)activity.The mφ heterogeneity was demonstrated in lymphomyeloid tissue(LT)as well as in liver with histologic and cytochemic approaches,by which 5 types of mφs,I.e.Reticular/fibrous macrophage(RFmφ),shuttle macrophage(Smφ),round red macrophage(RRmφ),round yellow-red macrophage(RYRmφ)and pigment macrophage(PM),were identified.PM originated from RFmφs through the intermediate stages of Smφ,RRmφ and RYRmφ.The total amount of round macrophages(Rmφs)and PMA formation was closely related,PMA could not form if the amount of Rmφs was not high enough,and PMA had a tendency of migrating out of LT during the late experiment.The functions attributed to PMA were discussed.