Distribution of Carotenoids and Protective Effects of Zeaxanthin on Retina of Ayu Sweetfish (Plecoglossus altivelis)

Dietary carotenoids enhance SWS1 expression in female western mosquitofish (Gambusia affinis) but do not impair their likelihood of pregnancy in the presence of male guppy

The various cone opsin genes are responsible for distinct ecological tasks, with the altered expression profiles in teleost fishes representing an excellent paradigm for studying how fishes can quickly adapt to diverse habitats within their lifecycles. The molecular mechanisms underlying transcriptional switching among cone opsin genes are still being investigated, but factors such as light conditions, developmental stages, sex hormones, and diet are known to play a role in changing cone opsin expression profiles. Based on previous research on guppies, we hypothesized that a diet rich in carotenoids could enhance expression of the opsin gene LWS in western mosquitofish (Gambusia affinis) and potentially influence female mate choice. We raised female western mosquitofish under low-level or high-level carotenoid diets and then conducted female mating preference experiments, with or without the presence of male guppy (Poecilia reticulata). qPCR revealed that high carotenoid intake upregulates SWS1 rather than LWS transcription. This positive feedback loop may promote foraging efficiency and also protect the visual system from UV damage. The carotenoid diets had no effect on pregnancy likelihood, possibly because UV light is not a critical cue in western mosquitofish female mate choice and/or the light source we used did not encompass the UV spectrum. Presence of male guppies had no effect on pregnancy likelihood, though a previous study reported that it significantly reduced brood size. Therefore, interactions between male guppies and western mosquitofish likely reduces the number of copulations and/or disrupts parenting to reduce the number of offspring.

The effects of nanoplastics and microcystin-LR coexposure on Aristichthys nobilis at the early developmental stages

Nanoplastics (NPs) and microcystin-LR (MC-LR) are two common and harmful pollutants in water environments, especially at aquafarm where are full of plastic products and algae. It is of great significance to study the toxic effects and mechanisms of the NPs and/or MC-LR on fish at the early stage. In this study, the embryo and larvae of a filtering-feeding fish, Aristichthys nobilis, were used as the research objects. The results showed that the survival and hatching rates of the embryo were not significantly affected by the environmental concentration exposure of these two pollutants. Scanning electron microscopy (SEM) observation displayed that NPs adhered to the surface of the embryo membrane. Transcriptomic and bioinformatic analyses revealed that the NPs exposure activated neuromuscular junction development and skeletal muscle fiber in larvae, and affected C5-Branched dibasic acid metabolism. The metabolic and biosynthetic processes of zeaxanthin, xanthophyll, tetraterpenoid, and carotenoid were suppressed after the MC-LR exposure, which was harmful to the retinol metabolism of fish. Excessive production of superoxide dismutase (SOD) was detected under the MC-LR exposure. The MC-LR and NPs coexposure triggered primary immunodeficiency and adaptive immune response, leading to the possibility of reduced fitness of A.nobilis during the development. Collectively, our results indicate that environmental concentration NPs and MC-LR coexposure could cause toxic damage and enhance sick risk in A.nobilis, providing new insights into the risk of NPs and MC-LR on filtering-feeding fish.