Down to size: Exploring the influence of plastic particle Dimensions on physiological and nervous responses in early-stage zebrafish.

The chorion is the first protective barrier set to prevent numerous pollutants from damaging the developing embryo. However, depending on their size, some nanoplastics (NPs) can pass through this barrier and reach the embryo, while all microplastics (MPs) remain on the outside. This study brings a straight approach to compare MPs and NPs, and assess their direct and indirect effects on zebrafish embryos and larvae. Zebrafish eggs were exposed before 2 h post fertilization (hpf) to polystyrene MPs (5 µm) and NPs (250 nm) at a concentration of 1000 µg/L until 96 hpf. Physiotoxicity and neurotoxicity were assessed prior and post-hatching through several biomarkers. Response to hypoxia (upregulation of hif-1aa and hif-1ab) were found in embryos exposed to MPs, and partly found in those exposed to NPs. Embryos exposed to NPs showed significant tachycardia, reduced O2 consumption and increased apoptosis in the eyes, whereas MPs affected the expressions of all genes related to the neurodevelopment of embryos (elavl3, pax2a, pax6a, act1b). Post-hatching, physiological responses were muted. MPs and NPs exposures ended by evaluating larval behaviours during dark-and-light cycles. Both sizes of plastic particles negatively affected the visual motor response (VMR) and vibrational startle response (VSR). Thigmotaxis levels were significantly increased by NPs whereas MPs showed anxiolytic properties. This study shows that both MPs and NPs affect the physiology and neurodevelopment of zebrafish at different levels, before and after hatching.

Single or Combined Dietary Supply of Psidium guajava and Phyllanthus amarus Extracts Differentially Modulate Immune Responses and Liver Proteome in Striped Catfish (Pangasianodon hyphophthalmus).

Guava Psidium guajava L (Pg) and bhumi amla Phyllanthus amarus Schum. et Thonn (Pa) are well-known plants in traditional medicine. However, the capacity of these plants for improving the immune system of aquatic species has received less attention so far. This study aimed to investigate the effects of single supply or mixture of Pg and Pa extracts on immune responses, disease resistance and liver proteome profiles in striped catfish Pangasianodon hypophthalmus. Fish were fed diets including basal diet 0% or one of three doses of each plant extract, either alone or in mixture, 0.08, 0.2, or 0.5% Pg, Pa or mixture (Pg:Pa, v/v) for 6 weeks. The immune parameters (respiratory burst activity (RBA); nitric oxide synthase (NOS), total immunoglobulin, lysozyme, and complement activities) were examined at W3, W6 post-feeding, and after challenge test. The growth parameters and the challenge test with Edwardsiella ictaluri were done at W6. The liver proteome profiles were analyzed in W6 at 0.08 and 0.5% of each extract. The results showed that extract-based diets significantly improved growth parameters in the Pg0.2 group compared to control. The cellular immune responses in spleen and the humoral immune responses in plasma were significantly improved in a dose and time-dependent manner. Diets supplemented with single Pg and Pa extracts, and to lesser extent to combined extracts, could significantly decrease the mortality of striped catfish following bacterial infection compared to control. The proteomic results indicated that some pathways related to immune responses, antioxidant and lipid metabolism were enriched in liver at W6. Several proteins (i.e., CD8B, HSP90AA1, HSP90AB1, PDIA3, CASP8, TUBA1C, CCKAR, GNAS, GRIN2D, PLCG1, PRKCA, SLC25A5, VDAC2, ACTN4, GNAI2, LCK, CARD9, NLRP12, and NLRP3) were synergistically upregulated in mixture of Pg and Pa-based diets compared to control and single dietary treatments. Taken together, the results revealed that single Pg and Pa extracts at 0.2 and 0.5% and their mixture at 0.08 and 0.5% have the potential to modulate the immune mechanisms and disease resistance of striped catfish. Moreover, the combination of Pg and Pa in diets suggested positive synergistic effects liver proteome profile related to immune system processes.