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.

The objective of this study was to investigate the effluent treatment from Nile tilapia farming in a biofloc system with a consortium of microalgae (Chlorella vulgaris) and zooplankton (Daphnia similis). Thus, integrated cultures of C. vulgaris and D. similis were performed in two forms of wastewater treatment: sedimentation (S) and non-sedimentation (NS), in four different salinities (1, 2, 3 and 4 g L⁻¹). Water quality, growth of D. similis, behaviour of C. vulgaris, efficiency of removal of nitrogen compounds, orthophosphate, and total suspended solids (TSS) were measured. D. similis had higher density in 3NS (p < 0.05), while population die-off occurred in 4S and 4NS. The 2S and 1NS combinations stood out in bioremediation, achieving removal of up to 70.37% nitrate, 75.74% orthophosphate, and 90.74% TSS. 2S and 3S cultures became self-sufficient from day 21. Thus, the Chlorella-Daphnia consortium using 3NS allowed better production of D. similis, whereas salinities 2 g L⁻¹ (S) and 1 g L⁻¹ (NS) provided better bioremediation, and the use of S wastewater improved the sustainability of the system. These results contribute to a better evaluation of cultures in consortia of organisms for the treatment of aquaculture wastewater and the production of live feed for aquaculture. GRAPHICAL ABSTRACT

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.