In extensive culture operation, the shrimps are fully dependent on the availability of natural food in the pond. As the shrimps grow, the amount of natural food organisms become insufficient to meet the growing demand. The growth of shrimps slow down when natural food diminishes. This usually takes place towards the second month of the culture period depending on the stocking density and fertility of the pond. In order to maintain optimum growth rate throughout the culture period, additional feeds should be given in the form of supplemental feeds, fertilization of pond water or transfer of stock to new ponds with natural food. Supplemental feeding is recommended when cheaper feeds (eg., trash fish) are available easily. Pond fertilization on the other hand, is commonly employed when the natural food in the pond is diminishing. However, the latter practice sometimes cannot supply sufficient quantity of natural food in the pond is almost completely consumed prior to fertilization.
Transferring of stock to a new pond with luxuriant growth of natural food has been found to be conducive to shrimp growth. Pond production of shrimp is comparable or sometimes even better than those fed with supplementary feeds. Other advantages are: (i) survival rate is significantly improved due to effective eradication of predators and competitors, (ii) maximum growth rate is usually attained because the shrimps are transferred to a more growth promoting habitat free from pollution stress, (iii) reduce the frequency of soft-shelling condition. The disadvantage, however, is that mortality during transfer is unavoidable especially when the shrimp have newly molted.
In semi-intensive culture operation (2–4 shrimps/m2), there are no significant difference between feeding the stocks after 2 months of culture and transferring them to another pond using the modular system described above. Due to high cost of supplementary (formulated) feeds, it appears that the modular system is economically more viable than using supplemental feeds.
