Effects of low salinity on gill and liver glycogen metabolism of great blue-spotted mudskippers (Boleophthalmus pectinirostris)

This study investigated the effects of low salinity exposure on glycogen and its metabolism biomarkers, glycogen synthase (GS) and glycogen phosphorylase (GP), representing glycogen synthesis and catabolism, respectively, in the gills and liver of great blue-spotted mudskippers (Boleophthalmus pectinirostris). The fish were accumulated at 10‰ salinity seawater for 1 week, then 270 healthy great blue-spotted mudskippers with similar size were randomly transferred to 10‰ (control group) or 3‰ (low salinity group) seawater for 72-hour stress experiment. Fish significantly elevated their blood glucose levels 12 h after low salinity challenge. At the end of experiments, a decrease in liver glycogen contents was observed in both the control and low salinity groups, the latter showing a pronounced decrease, while the gill glycogen contents were not changed for either group. The mRNA abundance and enzyme activity of GS and GP were both elevated in gill tissues, showing a rising glycogen synthesis and catabolism, probably resulting in the unchanging gill glycogen content. While in liver tissues, the mRNA abundance and enzyme activity were decreased for GS and increased for GP, showing a net increase for breaking down glycogen in liver, probably for supplying a sufficient glucose level for gills and other tissues/organs involved in the response to salinity changes.