These farming systems comprised mainly fishponds, fertilized to produce natural plankton as feeds and also supplied with supplemental feed, and cages in which fish were usually supplied with more complete formulated feeds. In these situations, there is sometimes a tendency to overfeed fish in the belief that this will lead to increased harvests. This situation complicates estimation of feed conversion efficiency. Methods for the genetic improvement of feed conversion efficiency in farmed fish were not available when GIFT were developed and are still under development.