Linking energy metabolism and locomotor variation to osmoregulation in Chinese shrimp Fenneropenaeus chinensis.

Although previous studies have shown that salinity exposure affects shrimp respiration, little is known of the properties and variation of anaerobic and aerobic metabolism in tissues, and in particular of the relationship between energy metabolism and shrimp locomotion. To examine the relationship between energy metabolism and locomotor variation during osmoregulation, Chinese shrimp Fenneropenaeus chinensis were held at 30‰, 25‰, 20‰, 15‰, and 10‰ salinity for 15 days, after which the activities of key enzymes involved in glycolysis, tricarboxylic acid cycle, and electron transport chain in posterior gills, pleopods, and abdominal muscles were determined. Hemolymph osmolality, oxygen consumption rates, swimming and tail-flipping abilities were also obtained. Results showed that hemolymph of F. chinensis was isosmotic to brackish water at 25‰ salinity. The rate of oxygen consumption increased by 27.8% to 126.0% during osmoregulation. Activities of citrate synthase (CS) and cytochrome c oxidase (COX) increased in posterior gill rather than muscles during osmoregulation. In muscles, CS and COX activities decreased by 16.6% to 59.11% at 15‰ and 10‰ salinities, but phosphofructokinase (PFK) and lactate dehydrogenase (LDH) activities decreased by 13.2% to 44.5% at 10‰ salinity. Swimming abilities were positively correlative with CS and COX activities of pleopod muscle. Tail-flipping abilities increased with PFK and LDH activities of abdominal muscles. These findings suggest that shrimp increase reliance on aerobic metabolism for fueling osmoregulation. There is an energetic trade-off between gill and muscles under salinity exposure. The energetic depression of muscles results in the reduction of shrimp locomotion during osmoregulation.