Hydrobiologia

da Costa, Igor David; da Silva, Letícia Versiani Gomes; dos Anjos Santos, Anna Clara; dos Santos Nunes, Natalia Neto; Costa, Leonardo Lopes; da Silveira, Leonardo Serafim; Zalmon, Ilana Rosental

doi: 10.1007/s10750-025-05983-2pmid: N/A

This study investigated the presence of microplastics (MPs) in fish from streams with different levels of forest cover in the southwestern Amazon. Fish were collected using seine and dip nets along an 80 m stretch of 20 streams. Among the 584 fish analyzed, 196 individuals (33%) contained microplastics in their digestive tracts, with MPs detected in all species examined. Blue and black fibers < 0.1 mm were the predominant types of MPs found in the analyzed fish species. Polyester, polyamide and polypropylene were identified as the main polymers. Vegetation cover in micro-watersheds influenced MPs ingestion by Amazonian stream fish, with more MPs found in the digestive tract of fishes from deforested areas compared to those from forested ones. Environmental characteristics, such as seasonal precipitation patterns, and ecological traits, including feeding strategies and habitat use, were also important drivers of MP incorporation by fish species. Our results indicate that fish from sparsely forested streams could become even more susceptible to microplastic contamination as the frequency and intensity of drought and flood events change.

Weber, Vinicius; Alonso, Felipe; Godoy, Robson S.; Lanés, Luis E. K.; Pires, Mateus M.; Gava, Adriana; Stenert, Cristina; Maltchik, Leonardo

doi: 10.1007/s10750-025-05962-7pmid: N/A

For annual killifishes in temporary wetlands, diapause induction during embryonic development is considered a bet-hedging strategy to endure unpredictable dry periods. However, the extent to which killifish embryos exhibit developmental variation—and the underlying drivers—remains unclear. We assessed diapause induction patterns of the endangered killifish Matilebias cyaneus across three hydrological phases (early-wet, drying, late-wet) of a temporary wetland. Wild egg clutches with known parentage were incubated under common-garden conditions to monitor entry or skipping of early and mid-embryonic diapause (diapause I and II). Most embryos skipped both diapauses in the early-wet phase, while mixed trajectories were observed in drying and late-wet phases. Interestingly, this variation may reflect not only environmental phase alignment but also maternal age-related epigenetic effects, which have been shown to influence diapause regulation in annual killifishes. These findings support the idea that fine-tuned bet-hedging strategies may evolve through natural selection acting on maternal programming mechanisms, rather than on direct embryo sensing of hydrological conditions. Understanding survival strategies of wetland taxa across seasonal gradients remains key to predicting species resilience under climate-driven hydroperiod shifts.

Khan, Mohsin; Johnson, Kelly S.

doi: 10.1007/s10750-025-05932-zpmid: N/A

The potential effects of microplastics (MPs, < 5 mm) in aquatic systems, especially through interactions with other environmental stressors, are a growing concern. In a prior study, we found that ingested polyethylene MPs altered the toxicity of Bacillus thuringiensis israelensis (Bti) to the midge Chironomus riparius, with larger particles (125 µm) increasing Bti toxicity and smaller particles (34–50 µm) reducing it. The current study describes the effects of the same MP particles on the toxicity of spinosad, an insecticide with a neurotoxic mode of action. Large and small plastic particles were fed to larvae that were simultaneously exposed to spinosad (0, 10, 20, 40, 53, and 67 mg/L) for 21 days. Natural kaolin particles (1–10 μm) were used as a nonplastic control particle. Spinosad alone reduced larval survival and adult emergence as expected, while ingested kaolin and MPs had no effect by themselves. In contrast to our findings with Bti, none of the particles altered spinosad toxicity to larvae at 7 days. However, the smaller-sized MP reduced adult emergence compared to spinosad alone. This pattern suggests that MPs can alter spinosad efficacy, but the effect depends on particle size, and the physiological mechanism appears to be different from those observed with Bti. These findings reinforce the importance of using a variety of sublethal toxicological endpoints and accounting for interactions with co-occurring contaminants for assessing risks associated with MPs in freshwater systems.