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This study aimed to evaluate the planktonic composition (phytoplankton, protozooplankton and zooplankton) in Oreochromis niloticus culture in low salinity (10 g L−1) biofloc with different molasses application rates. Fingerlings of Nile tilapia (3.15 ± 0.5 g) were cultured for 70 days in a randomised design with two application rates: 30% and 50% molasses application of the total daily feed. Chlorella vulgaris was supplemented every 5 days (5 × 104 cells mL−1) and plankton samples were collected weekly. Evaluating planktonic data, diversity was considered low, and there was no significant difference (p < 0.05) between liquid molasses application rates. However, in the analysis of similarities, a difference was observed in relation to time. Cluster analysis identified two groups for phytoplankton and zooplankton. Chlorophyta group was the most abundant (>40%), with Chlorella genus being the main responsible for this dominance. In the zooplankton and protozooplankton communities, the genera with the highest abundance were: Anuraeopsis (42.60–76.96%) and Paramecium (70.15–81.25%), respectively. For zootechnical performance, the treatment with molasses application rates of 30% showed lower feed conversion ratio (2.06 ± 0.17). The results suggest that there were significant changes in the plankton composition throughout the culture of Nile tilapia in the biofloc system, however, without any influence of the molasses application rates. [ABSTRACT FROM AUTHOR]

Knowledge about phytoplankton communities is important for aquaculture due to their influence on environmental variables. The goal of the study was to evaluate the ecological effect of seaweed Gracilaria birdiae at three different densities: 2.5 (LG2.5); 5.0 (LG5.0) and 7.5 kg m−3 (LG7.5), on water quality variables and the phytoplankton communities in integrated aquaculture systems (shrimp and seaweed) with a control (without seaweed) (LB) using biofloc technology. Settleable and total suspended solids were significantly correlated with the phytoplankton groups. In addition, orthophosphate was the main variable controlling phytoplankton growth and gross primary production. No significant differences were identified among the treatments in terms of the phytoplankton assemblages (p > 0.05) but differences were found between the communities (ANOSIM, R global = 0.873) in relation to the days of the experiment. However, the LG2.5 treatment had higher diversity and lower species dominance, as well as higher productivity and final shrimp weight. The results indicate that seaweed inhibit phytoplankton growth, mainly of toxic species. They suggest that phytoplankton composition in integrated aquaculture systems in the presence of seaweed at a density of 2.5 kg m−3 is more diversified and provides better water quality and shrimp performance by inhibiting the abundance of harmful species. [ABSTRACT FROM AUTHOR]