We investigated ammonium N (NH -N) and phosphate P (PO -P) uptake by unicellular algae as a method for removing exceisive nitrogen (N) and ph%sphorus (p) from larval shrimp rearing water and evaluated the feasibility of using algae to manage the water quality. Tetraselmis tetrad&e, Nannochloropsis oculata, Isochrysis sp. and Chaetoceros gracilis were considered to be suitable algae to keep the N and P content of the rearing water low. N and P uptake of these algae from culture media and their food value to shrimp Metapenaeus ensis larvae were examined by uni-algal culture or feeding experiments. Furthermore, NH -N and PO -P uptake by N. oculata from the larval rearing water was measured to determ&e the effe&s of algal feeding. Most of the NH -N and PO -P contained in the culture media were utilized by these algae by 16 to 27 day: after inocilations. Their nutritional value, in decreasing order, was estimated to be: C. gracilis, Z tetrathele, Isochrysis sp.; and N. oculata seemed to be very low. However, a mixed feeding of N. oculata and an artificial diet provided better growth and higher survival rate of larvae than did each of them separately. Moreover, NH -N and PO -P content of the larval rearing water was kept lower in the mixture feeding thr& in the feeding of the artificial diet only. Therefore, even if the alga had low nutritional value for the larvae, adding it to the rearing water was useful in keeping the N and P content low aad improving the s&ival rate of &imp larvae.