Inducible defenses occur in various taxa of prey organisms. Many phytoplankton species, including the freshwater Chlorophyta Tetradesmus spp., can form defensive morphs under the zooplankton‐released grazing cues. However, definite statements on the actual mechanisms of inducible defense in phytoplankton are quite deficient. In the present study, the defensive mechanism of Tetradesmus obliquus (formerly known as Scenedesmus obliquus) induced by Daphnia infochemicals was analyzed through multifaceted analyses integrating physiological and biochemical monitoring, transcriptomics, and metabolomics. Results showed that the upregulated genes encoding G protein‐coupled receptor and phospholipase C were involved in the perception and transduction of grazing cues, and the transcripts related to extracellular polysaccharides formation and transductions were upregulated. The results provided molecular evidence for the role of extracellular polysaccharides in colony formation. Increased lipid content revealed through metabolomics suggested higher investment in lipid biosynthesis within colonial cells, whereas the downregulation of ribosome‐related pathways indicated less allocation of energy and resources to protein biosynthesis. The significant increase in indole‐3‐acetic acid content indicated that growth was activated under grazing cues. This study provided essential information on the inducible defensive mechanism of Tetradesmus and direct evidence for the intracellular reallocation of resources and energy owing to the defensive colony formation, which had considerable implications for enriching the theory of inducible defenses at the molecular level.

Microplastics represent an emerging threat to aquatic environments and organisms, as they infiltrate water systems, are ingested by marine species, and cause physical harm, endocrine disruption, and bioaccumulation up the food chain, potentially impacting biodiversity and human health. Aquatic ecosystems face considerable harm from microplastic pollution because fish in the early developmental stages, including embryos, larvae, and juveniles, are more susceptible due to their immature physiological and detoxification systems. This review aims to comprehensively explore the impacts of microplastics on the early life stages of fish. Aquatic environments receive primary and secondary MPs from urban runoff and industrial waste, together with degraded plastics, which affect fish embryos and larvae via direct ingestion, surface adhesion, and trophic transmission pathways. The physical impact of MPs causes digestive tract blockages that reduce hatching success and create developmental problems in fish organs, but chemical toxicity develops from plasticizers, heavy metal leaching, and pollutant adsorption, which causes oxidative stress, endocrine disruption, and metabolic dysfunction. Survival rates decrease because exposure causes fish to perform poorly during swimming activities and make limited efforts to avoid predators. The small dimensions and high chemical reactivity of MPs increase their bioavailability, which promotes tissue penetration and leads to accumulation at different levels of the food chain. This comprehensive review emphasizes that we need to establish uniform detection protocols, long-term exposure research, and effective strategies to control MP pollution. The resolution of these difficulties remains essential for protecting fish populations, as well as for protecting biodiversity and minimizing seafood contamination risks to human health.

Freshwater salinization is a growing environmental issue caused by various anthropic or natural factors that lead to changes in water chemistry and physical conditions, affecting the survival and diversity of phytoplankton. In this study, we tested the physiological, morphological and interspecific competition of the freshwater cyanobacterium Microcystis aeruginosa and the green algae Scenedesmus obliquus to salinity stress. Results demonstrated that increasing salinity had a significant negative effect on the growth of M. aeruginosa and S. obliquus. M. aeruginosa showed a decline in growth rate with increasing salinity, while S. obliquus showed a lower growth rate under salinity stress but with no significant difference between the two salinity groups. In cocultures, S. obliquus outcompeted M. aeruginosa, and the displacement was accelerated with increasing salinity. The photosynthetic performance of both algae was affected by salinity, the presence of competitors, and the cultivation time. S. obliquus showed morphological variations under salinity stress and the presence of a competitor. The study suggests that salinity stress and competition can have a significant impact on the growth and performance of algae species. The findings of our study suggest that the salinization of freshwater can impact the interspecific interactions among phytoplankton, which play a crucial role in the functioning of freshwater ecosystems.