Euryhaline fish larvae ingest more microplastic particles in seawater than in freshwater

Abstract

Microplastic (MP) pollution is a major concern in aquatic environments. Many studies have detected MPs in fishes; however, little is known about differences of microplastic uptake by fish in freshwater (FW) and those in seawater (SW), although physiological conditions of fish differ significantly in the two media. In this study, we exposed larvae (21 days post-hatching) of Oryzias javanicus (euryhaline SW) and Oryzias latipes (euryhaline FW), to 1-µm polystyrene microspheres in SW and FW for 1, 3, or 7 days, after which, microscopic observation was conducted. MPs were detected in the gastrointestinal tracts in both FW and SW groups, and MP numbers were higher in the SW group in both species. Vertical distribution of MPs in the water, and body sizes of both species exhibited no significant difference between SW and FW. Detection of water containing a fluorescent dye revealed that O. javanicus larvae swallowed more water in SW than in FW, as has also been reported for O. latipes. Therefore, MPs are thought to be ingested with water for osmoregulation. These results imply that SW fish ingest more MPs than FW fish when exposed to the same concentration of MPs.

Short-term microplastic exposure in fish larvae: The ingestion, elimination, and initial effect on japanese medaka (Oryzias latipes) larvae

“…Thus, MP particles exposed to larvae in this research were considerably minuscule to be confused as food. Consequently, we believe that the primary factor influencing MP ingestion in Oryzias latipes larvae in this study is water drinking for the osmoregulatory process, as reported in our previous study [14]. An earlier study by Kaneko and Hasegawa stated that water drinking of O. latipes larvae in freshwater was proven, although the rate is lower than that in seawater [17].…”

“…MP extraction and counting were performed as described in the previous report [14], with several modifications. For MP extraction, larvae samples from the exposure phase (Day 1 and 3) and elimination phase (Days 4 and 6) were evenly crushed in 20 mM HEPES solution.…”