The population growth rate (mean + standard error, based on three replicates) achieved by B. calyciflorus and B. angularis cultured at different Scenedesmus obliquus levels and inoculation densities. The inoculation densities used for B. calyciflorus are as follows: I − 100% B. calyciflorus; II − 75% B. calyciflorus; III − 50% B. calyciflorus; IV − 25% B. calyciflorus. For B. angularis, the inoculation densities A, B, C and D represent 100, 75, 50 and 25% B. angularis, respectively. Shown are the values mean + standard error based on four replicates. Small letters indicate means that are similar (same letter) or different (different letters) among three food levels when inoculated at each of four densities (LSD multiple comparison), and capital letters indicate means that are similar (same letter) or different (different letters) among four inoculation densities when fed 0.5 × 10⁶ (white bars), 1.0 × 10⁶ (grey bars) and 2.0 × 10⁶ (black bars) cells ml⁻¹ of S. obliquus, respectively (LSD multiple comparison).