A preliminary study of the effects of poly-methylmethacrylate microplastic ingestion on the digestive physiology and growth rates of a tropical ancestral fish (Atractosteus tropicus)

This study evaluated the effects of polymethylmethacrylate (acrylic) microplastics (PMMA-MPs) on the growth, survival, digestive enzyme activity, and intestinal microbiota of tropical gar (Atractosteus tropicus) fed diets enriched with different percentages of PMMA-MPs (0.0, 0.25, 0.50, 0.75, and 1.00%) for 60 days. Fish initial weight was 4.80 ± 1.18 g and a total length of 11.51 ± 0.89 cm, respectively. Final growth showed a significantly lower weight at 0.25% compared to 1.00% PMMA-MPs treatments (23.21 ± 8.33 and 30.33 ± 12.14 g, respectively; p = 0.02), however, without differences to the control group (p = 0.44). The enzymatic activity of acid proteases, alkaline proteases, trypsin, chymotrypsin, L-aminopeptidase, and α-amylase showed significant differences among treatments (p < 0.05), except in lipases (p = 0.83). A preliminary intestinal microbiota analysis showed higher values of the α diversity indexes (Chao, Shannon, Simpson, and Evenness) in the control groups and 1.00% PMMA-MPs and lower at 0.25, 0.75, and 0.50% PMMA-MPs. The relative abundance was represented mainly by Firmicutes in the groups with 0.25, 0.50, and 0.75% PMMA-MPs (between 67 and 88% coverage) compared to controls and 1.00% PMMA-MPs (23 and 13%, respectively). PMMA-MPs exposure affects the hydrolysis and absorption of nutrients, compromising the nutrition and, thus, the health of A. tropicus juveniles.