Assessment of microplastic ingestion in peixinho ('Little Fish'): post-larval and juvenile Gobiidae from São Tomé and Príncipe

Microplastic pollution is a growing global concern, with significant consequences for aquatic ecosystems and human food security. Although microplastic ingestion is well documented in aquatic organisms, it has not been previously assessed in post-larval and juvenile amphidromous gobies (Sicydium bustamantei, Sicydium brevifile, and Awaous spp.) endemic to São Tomé and Príncipe. These species sustain the traditional goby-fry fishery (locally known as “peixinho” fishery), yet their exposure to anthropogenic pollutants has remained unexplored. This study provides the first evidence of widespread microplastic ingestion in these species across multiple rivers (Lembá, Paga Fogo, Iô Grande and Martim Mendes) and seasons (dry and wet). A total of 703 anthropogenic particles were recovered, with 72.5% of individuals containing at least one particle. Encounter rates (181-209%) ranked among the highest reported globally. Sicydium bustamantei ingested significantly more microplastics than Awaous while S. brevifile showed a higher likelihood of particles ingestion compared to Awaous. Fibres dominated (87%), with rayon identified as the most abundant polymer, together with cotton and cellulosic material, reflecting local domestic practices such as washing clothes and utensils directly in rivers. Black (46%) and blue (39%) were the predominant colours, consistent with textile-derived sources. Particle sizes ranged from 40 to 25790 μm, with larger particles (≥1000 μm) prevailing. Sicydiym bustamantei and Awaous ingested significantly larger particles than S. brevifile, while individuals sampled from Martim Mendes River ingested significantly larger particles than the ones in Iô Grande. Ingestion was detected across all sites and species, confirming widespread contamination. These findings demonstrate that severe microplastic pollution is occurring in the rural freshwater systems with minimal industrial activity of São Tomé. Given the vulnerability of early life stages and the socioeconomic reliance on these species, this level of contamination poses serious risks of physiological stress, toxicity and trophic transfer. Addressing these challenges is crucial for both ecological conservation and the development of effective waste management and pollution mitigation strategies in São Tomé.