Rice and fish are staple foods in the Philipines as well as in other parts of Southeast Asia, where calorie/protin malnutrition is a serious probem. Milkfish, (Chanos chanos) is well-liked by the masses and, therefore, ti could be a good source of protein and calories. In traditional culture, milkfish yield is rather low and limited to the carrying capacity of the culture ponds (Lim et al., 1979). To increase production through intensive culture, a diet to supplement the natural food in the ponds is needed. However, practical diet formulation is hampered by the lack of knowledge about the nutritional requirements of milkfish. The present study was carried out to determine optimum protein, fat, carbohydrate and energy levels for milkfish fingerlings using growth, survival, and body composition as parameters for determining the effectivity of the diets. The response surface analysis was explored graphically using a "freehand" technique to search for optimal diets with respect to dietary levels of protein, fat and carbohydrates.

In order to investigate the effect of different protein/energy levels of diets (two commercial and one laboratory) on voluntary feed intake and energy partitioning in tilapia (O. niloticus), 15 fishes with an initial body mass of 33 g were reared individually in respirometric chambers for 42 days and offered 3 diets ad libitum. The protein contents of the diets were 36.1, 33.8 and 36.8% (dry matter base); the energy content 18.9, 18.4 and 19.2 kJ GE/g and 11.7, 10.5 and 15.4 kJ ME/g. The initial body composition and energy content was estimated from a control group. Feed consumption was recorded for each individual fish. Body mass development was monitored weekly. At the end of the experiment, the fishes were sacrificed and their chemical composition (protein as N.6.25, lipid, ash) and gross energy content were determined. To establish energy budgets, ingestion (I) was calculated from feed intake, retention (P) from accretion in the carcass, heat production (R) from oxygen consumption (indirect calorimetry) and apparently non-utilized energy (faecal and non-faecal losses, U) by difference from energy ingestion. In the beginning, food consumption amounted to ~5% body mass equivalent (BME) per day for all groups and gradually decreased to 2.5, 2.8 and 1.6% BME by the end of the experiment. While the food consumption was significantly different between the treatments, there were no significant differences in the body mass development. Average final body mass was 98.6, 93.8 and 103.7 g. Energy retention was 29.7, 29.2 and 44.4% of GE ingested; heat dissipation 32.1, 27.9 and 36.0%; faecal and non-faecal losses 38.2, 43.2 and 19.6%. For all energy budget parameters, values for the laboratory diet were significantly different from those of commercial feeds 1 and 2. Calculation of metabolizable energy from ingested feed revealed no significant differences in the energy uptake, suggesting that the voluntary feed uptake was controlled by the demand for metabolizable energy. The fishes were able to completely compensate for the lower ME content of the commercial feeds by increasing voluntary feed intake.