Fish-processing wastes as an alternative diet for culturing the minute rotifer Proales similis de Beauchamp

We evaluated the suitability of fish waste diet (FWD) for culturing the minute rotifer Proales similis through the observation of their population growth and particle size selective feeding. A total of five treatments either with Nannochloropsis oculata or FWD (0.75 and 0.50g/L) or the combination of N.oculata and FWD were set up in triplicates. P.similis were cultured in diluted natural seawater (8g/L salinity) and 26 +/- 1 degrees C with the diet treatments being applied randomly. We daily monitored the rotifer density, the number of bacteria and the water quality in all the cultures. The population density of P.similis increased exponentially in all treatments, while the mean growth in FWD 0.75g/L was significantly higher (p<.05) than that in the control. Addition of N.oculata to FWD resulted to lowered P.similis population growth. Bacterial colony count was high in FWD and introduction of P.similis to the diet decreased their density. The estimated bacteria ingestion rates were generally in the range of 6.03x10(2)-1.24x10(4) bacteria/rotifer/hr and there was a positive linear relationship between bacterivory and rotifer population growth. We also observed a shift in the particle size distribution with a reduction in the frequency and concentration of small-sized particles (<2.5m) at day 6. These results accentuate the potential of fish-processing waste as diet for culturing P.similis which feeds on bacteria and small particles (2.5m) that are by-products of degradation of this diet.