Occurrence and Characteristics of Microplastics Contamination in Different Intensive Aquaculture Systems Nearby the Yangtze Estuary, China.

Microplastics (MPs) pollution has been extensively investigated in natural fishery waters, but studies on intensive aquaculture systems are scarce. Here, the occurrence and properties of MPs were investigated and compared between four different aquaculture systems nearby the Yangtze Estuary. The average MPs concentration was in order of recirculating aquaculture system (RAS, 1.67 particles/L) < aquarium (2.47 particles/L) < cement pond (10.09 particles/L) < earthen pond (13.81 particles/L). Compared to fragment MPs, fiber was the more abundant shape in aquarium (85.88%), RAS (77.61%) and earthen pond (68.13%). A total of six colors were found in four systems. The black MPs accounted for 56.86% and 47.45% in aquarium and RAS system, respectively. The high proportion of blue MPs was found in cement pond (37.65%) and earthen pond (40%). The most MPs sizes observed in the four systems were 43% of 50-300 µm MPs in aquarium; 44% and 30.19% of 300-1000 µm MPs in RAS and cement pond, respectively; and 30.19% of 3000-5000 µm MPs in earthen pond. For polymers, polypropylene occupied 47.83% in aquarium and RAS, 41.46% in cement pond and 27.79% in earthen pond. Proportion of rayon was highest in RAS (60.87%) and 34.04% of nylon was found in earthen pond. These results could provide scientific reference for further traceability and removal of MPs in different aquaculture systems.

Comparative metabolomics analysis of pigmentary and structural coloration in discus fish (Symphysodon haraldi).

Discus fish have a variety of body colors including pigmentary and structural colors, studies on specific substances and related metabolic pathways associated with body coloration, however, are scarce to the present. Here, we used single-color (blue, yellow and white) of discus for comparative metabolomics analysis of pigmentary and structural coloration. Statistical model showed significant separations between three colors of discus, suggesting the distinct metabolite profiles of discus pigmentary and structural colors. More astaxanthin was found in yellow discus, which might be the cause of yellow pigmentary color. Moreover, docosahexaenoic acid, arachidonic acid, linoleic acid, eicosapentaenoic acid, 1-stearoyl-2-oleoyl-sn-glycerol 3-phosphocholine, dodecanoic acid and myristic acid related to lipid metabolism and pathways of ABC transporters and biosynthesis of unsaturated fatty acids were more enriched in yellow discus. More adenine, xanthine and hypoxanthine were enriched in blue discus, which might account for the blue structural color. Moreover, amino acids associated with purine biosynthesis, e.g., L-alanine and L-isoleucine, were reduced but pathways of protein digestion and absorption, aminoacyl-tRNA biosynthesis, purine metabolism and glycine, serine and threonine metabolism were enriched in blue discus. Overall, these results reveal specific chromophores and related metabolic pathways involved in pigmentary and structural coloration of discus fish. SIGNIFICANCE: We detected specific chromophores present in skin of pigmentary and structural colors of discus and revealed potential metabolic pathways associated with body coloration. These results contribute to our understanding of the mechanism of body color formation in discus fish.