The short-term biological effects of different particle sizes of bioflocs on Litopenaeus vannamei

The biological effects of different particle sizes of bioflocs on Litopenaeus vannamei remain unclear. A 4-day short-term stress response experiment was conducted with small-sized group (SG), medium-sized group (MG), and large-sized group (LG), which were treated with bioflocs, and a control group (CG) treated with clear water. The diameters of the median particle size of SG, MG, and LG were 93.19 μm, 139.83 μm, and 173.09 μm, respectively; besides, the diameters of the coarse telomere of SG, MG, and LG were 181.40 μm, 279.60 μm, and 372.52 μm, respectively. The pathological observation of paraffin sections indicated varying degrees of tissue damage in SG, MG, and LG when compared with CG, with SG exhibiting more evident damage characterized by the presence of high-density vacuoles in the gill lumen. The activity of alkaline phosphatase and phenol oxidase exhibited varying degrees of fluctuation in all groups, with SG exhibiting a consistent downward trend. The activity of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, was enhanced by the influence of bioflocs. Additionally, the content of malondialdehyde in SG was significantly higher than that in MG and LG after 2–4 days of stress (P < 0.05). Gill transcriptome analysis showed that CA, PDIA3, V-ATPase, and genes related to oxidative phosphorylation pathway and tricarboxylic acid cycle were significantly up-regulated under the stimulation of bioflocs. Compared with MG, MHC, TnI, and GS were significantly down-regulated in SG. Compared with LG, DanjC9 was significantly down-regulated in SG. Overall, the results showed that the short-term biological effects of small-sized bioflocs on L. vannamei were the strongest.