It's not just synthetic microplastics: Multi-tissue approach reveals a wide range of transcriptional changes in European seabass exposed to viscose-rayon microfibres

The impacts of dietary viscose-rayon microfibres (RFs) on European seabass were evaluated on the growth performance and feed efficiency, as well as on gene expression patterns using tissue-specific customised PCR-arrays. Juveniles (5.8 g) were fed diets either without RFs (CTRL) or with increasing RF levels: RF1 (0.001 g/kg), RF2 (0.01 g/kg), RF3 (0.1 g/kg), to visual satiety for 68 days. While growth performance and feed efficiency remained unaffected by RF exposure, the hepatosomatic index (HSI) increased from 1.48 in RF1 and 1.55 in CTRL, to 1.98 in RF3 fish. HSI was related to hepatic transcriptional changes, such as activation of lipogenesis and mitochondrial respiration uncoupling, combined with overexpression of markers of cholesterol metabolism, and triacylglycerol- and fatty acid catabolism. RFs also affected the transcriptional profile of muscle, revealing enhanced regulation of positive and negative modulators of muscle growth. Several pro-inflammatory markers were altered by RF exposure, denoting an opposite regulation of immune response at systemic and local level, that contributed to discriminate CTRL_RF1 from RF2_RF3. The multi-tissue approach identified three distinct transcriptional signatures driven by 43 genes (CTRL_RF1, RF2, RF3). Intestine and muscle made a major contribution to this group separation. The findings indicate that RF exposure induces transcriptional changes but the absence of significant differences in growth performance, whole-body composition, and plasma immune parameters suggests that its physiological impact on fish health was minimal after 68 days of exposure.