Timing of Supplemental Feeding for Tilapia Production

The staged addition of feed to fertilized fish ponds was evaluated by adding fertilizers to 15 ponds stocked with Nile tilapia Oreochromis niloticus, then adding feed at half ad libitum rates once fish in the ponds reached a target weight. Each pond was stocked with 750 fish (3 fish/mz), and each treatment included three ponds with first feeding at (a) 50 g, (b) 100 g, (c) 150 g, (d) 200 g, and (e) 250 g. Ponds in Thailand (at the Ayutthaya Freshwater Fisheries Station, Royal Thai Department of Fisheries) were maintained for 236-328 d until the fish reached 500 g. Growth was similar for all treatments under fertilizer alone (1.17 g/d) and was also similar when feed was applied (3.1 g/d). Feed application rates averaged 1.17% BWld, indicating substantial use of natural food. Pond water quality did not deteriorate under supplemental feeding. Feed conversion rates averaged 1.03. Multiple regression indicated that 73.8% of the variance in growth was explained by design variables (feed input and days), while 86.2% of the variance in growth was explained by adding dissolved oxygen content and alkalinity into the equation. The most efRcient system was to grow fish to 100-150 g with fertilizers alone, then add feed. First adding feed (at 50% ad libitum) once fish reached 100 g produced the highest predicted annual revenues ($6,164 per hectare). Results of this experiment indicated that either critical standing crop occurred early (before the first fish sample) or did not occur at all in these ponds. The culture of Nile tilapia Oreochromis niloticus is commonly done worldwide in semi-intensive systems with fertilization. Additionally, feed may be provided for part or all of a grow-out to increase carrying capacity and growth of fish. Earlier experiments indicated that supplemental feeding in fertilized ponds resulted in significantly higher growth rates and greater yields than fertilization alone (Green 1992; Diana et al. 1994). Diana et al. (1994) determined that feeding rates of 50 to 100% ad libitum, combined with fertilization under optimal levels (Knud-Hansen et al. 1991), resulted in similar growth rates and yields. Fish in such systems grew to near 500 g in 160 d, I Corresponding author and yields approached 10,000 kgha. Since larger fish often fetch a higher market price, these yields may even be more valuable than increased biomass alone. Early growth of tilapia differed significantly in these feeding treatments, and it was unclear whether critical standing crop was ever reached, or whether it occurred in the first month of grow-out. Hepher (1978) proposed the concepts of critical standing crop (CSC) and carrying capacity as mechanisms to regulate and understand fish production in aquaculture ponds. According to his data from carp ponds, fish growth was similar in early grow-out stages regardless of inputs. Once the fish grew and reached critical standing crop, growth declined. This growth could 0 Copyright by the World Aquaculture Society 1996