Microplastics (MPs) in the form of microfibres (MFs) are of great concern because of their size and increasing abundance, which increase their potential to interact with or be ingested by aquatic organisms. Although MFs are the dominant shape of MPs ingested by sea cucumbers in habitats, their effect on sea cucumbers remains unclear. This study examined the effect of dietary exposure to MFs on the growth and physiological status of both juvenile and adult Apostichopus japonicus sea cucumbers. MFs were mixed into the diet of sea cucumbers for 60 d at environmentally relevant concentrations of 0.6 MFs g-1, 1.2 MFs g-1 and 10 MFs g-1. Dietary exposure to MFs, with concentrations at or above those commonly found in the habitats, did not significantly affect the growth and faecal production rate of either juvenile or adult sea cucumbers. However, a disruption in immunity indices (acid phosphatase and alkaline phosphatase activity) and oxidative stress indices (total antioxidant capacity and malondialdehyde content) was observed in juvenile and adult sea cucumbers, indicating that these indices might be useful as potential biomarkers of the exposure to MF ingestion in sea cucumbers. This study provides insights into the toxicity mechanism of MF ingestion in a commercially and ecologically important species.

Microorganisms colonize plastics in the aquatic environment but their composition on plastics used in aquaculture remains poorly studied. Microorganisms play a significant role in aquaculture in terms of water quality and the health of cultivated species. In the current study, we explored the composition of microorganisms on floating plastics and their surrounding water collected from ponds and open aquaculture areas. Using scanning electron microscopy, the diversity of microbial communities, primarily diatoms, and bacteria were identified on the plastic surfaces. Additionally, epifluorescence microscopy revealed that prokaryotes were colonized on all plastic samples from 0.1 to 29.27×10³ cells/cm², with a high abundance found in open aquaculture areas compared to ponds. Bacterial communities were characterized by 16S rRNA sequencing which showed that bacterial communities on plastics were dominated by Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria. The level of these microbial communities on the plastics differed from those found in the surrounding seawater samples and the abundance of potentially pathogenic bacteria was higher in plastics than in seawater samples. Moreover, hydrocarbon-degrading bacteria were more abundant in the investigated plastic samples than in the water samples. This study contributes to the knowledge regarding the plastisphere community in aquaculture.