ECONOMIC AND PRODUCTIVE EVALUATION OF EXTRUDED AND PELLETED FISH FEED IN BIOFLOC SYSTEM WITH TILAPIA Oreochromis niloticus FINGERLING
In comparison with traditional flow through or partial water change systems, biofloc technology (BFT) combines the reduction of water exchange with the removal of nutrients using heterotrophic bacteria, which can serve as complementary food by aquatic organisms, allowing better utilization of fish feed. Manufactured feeds, depending on its physical or chemical characteristics, can affect water quality, an in BFT it can increase turbidity or suspended solids volume, affecting visibility and diet consumption by fish, reducing growth. The present study was conducted to compare the economic and productive parameters of extruded and pelleted feeds in biofloc and a partial water change system with tilapia fingerling to identify the one that provides the greatest economic and productive benefits at this stage of growth.
An 8-week feeding trial was conducted in 0.35m3 concrete tanks with tilapia fingerlings (mean weight 25,06 ± 0,73 g). Fish were fed with extruded (ED) and pelleted (PD) diets containing 40% gross protein at 6% up to 3.5% daily feeding rate. The PD was obtained from the reprocessing (pelleted) the ED to keep the same nutritional value but different physical characteristics of the feed. Biofloc (BFT) had a C:N ratio of 15, using molasses (40% carbon) as carbon source, while partial water change system (PWC) consisted in daily 10-50% water renewals, both systems were kept with heaters (average temperature 27±1°C) and constant aeration. Productive (PP), water quality (WQP) and partial cost effectiveness parameters (PCE) were evaluated in a 2x2 (water system x feed) in a factorial design with three replications. The PCE were calculated based on the resources used and its relation to the biomass produced (Kg.m-3).
The results showed no statistically significant differences in the specific growth rates and food conversion rates of tilapia fingerlings between treatments (Table 1), although BFT/PD and PWC/ED reached the best values. The analysis of the PCE at the experimental level not only showed that BFT were up to 24% cheaper than PWC with both types of feeds, but also that BFT/PD was 7% cheaper than BFT/ED. The culture of tilapia fingerling improved in BFT even with the use of rapid sinking feed (pelleted feed), but with high water stability as was the case of PD.
