Giant bladder kelp (Macrocystis pyrifera) and maize (Zea mays) meals as nucleation sites for biofloc formation

Abstract

The aim of this study was to evaluate Macrocystis pyrifera and Zea mays meals as nucleation sites in biofloc formation. Bioflocs were studied for a period of 12 weeks, by measuring volume, dry weight, organic matter, and ash weight. These were induced by the addition of bacterial inoculum, molasses and both types of meals to fresh water. After 4 weeks, a total of 100 tilapia fingerlings (1.60 ± 0.02 g weight and 4.76 ± 0.03 cm length) were transferred to 100 L tanks by triplicate for each treatment. Mean ± SD values of temperature (26.3 ± 0.2 °C), dissolved oxygen (3.42 ± .0.07 mg L−1), pH (7.95 ± 0.04), salinity (0.47 ± 0.01) and ammonia (0.245 ± 0.012 mg NH3 L−1) were similar in both treatments. However, floc volume of M. pyrifera was significantly higher (116.1 ± 20 ml L−1) than Z. mays flocs (58.4 ± 7.7 ml L−1), but had lower dry weight (55 ± 0.5 mg g−1 in M. pyrifera vs. 61 ± 2.0 mg g−1 in Z. mays). Fish weight and length gain and survival were significantly higher (p < 0.05) in M. pyrifera floc (13.7 ± 1.3 g; 4.5 cm; 90 %) than in Z. mays (12.3 g; 8.5 cm; 56 %). Aggregated organisms were classified into major groups and were quantified and identified to a genus level. Ciliates were detected on week 1 and rotifers and nematodes were first registered on weeks 3 and 4. These three groups were present in both treatments but were more abundant in maize biofloc. In conclusion, both types of nuclei resulted in the formation of bioflocs rich in aggregated organisms, but nuclei of M. pyrifera produced a significantly higher performance of tilapia fingerlings, probably because of the higher nutritional content of kelp over maize meal and higher flotation of M. pyrifera flocs, which remained longer in suspension making them readily available to the fish. Keywords: Nucleation sites, Macroalgae, Macrocystis pyrifera, Tilapia, Oreochromis niloticus