Contribution No. 224 of the SEAFDEC Aquaculture Department.

The study was undertaken to determine the optimum combination of the frequency of water replenishment and fertilization that can yield the highest growth, survival, and gross production of milkfish. Results indicated that mean body weight and survival were not significantly different (P > 0.05) among the treatments. Gross fish production was higher in biweekly fertilization if considered as a single factor. However, when this was in combination with the weekly or biweekly water replenishment, similar gross fish production was attained. In any case, because biweekly fertilization has a better effect than a weekly schedule, the former should be used in combination with any other level of replenishment. A weekly water replenishment, however, is impractical in big pond areas of 5–10 ha compartments which are still common in some milkfish ponds in the Philippines. Therefore, biweekly water replenishment and fertilization with 16–20–0 at 50 kg ha^-1 would be reasonable.