Review on the osmoregulation and adaptation to salinity changes of Chinese mitten crab Eriocheir sinensis

Most Decapods species of the crustacean have comprehensive capacity of osmoregulation,and can adapt to a wide range of ambient salinties.It is significant to further understand the underlying mechanisms of their comprehensive ability of ambient salinities and helpful for the inland culture of some marine species by studying the osmoregulation and adaptive capacity of these species to ambient salinity changes.Chinese mitten crab,Eriocheir sinensis,has been well studied in many aspects related to the physiological responses to ambient salinity changes,and many useful literatures and findings have been accumulated.Therefore,E.sinensis could be regarded as an animal model for researching on osmoregulation mechanism of Decapods species.The current research on osmoregulation of E.sinensis is reviewed in the following aspects: 1) Effects of salinity on development,growth and energy metabolism of E.sinensis.At present,effects of salinity on larval development,growth and survival rates of different periods of larva and juvenile E.sinensis have been studied.Larval development of E.sinensis needs saline water,and therefore it can tolerate certain levels of ambient salinity.From zoea to megalopa,the salinity tolerance gradually increases.And at the juvenile period,they are able to adapt to freshwater environment.All these results can provide reference for juvenile crab cultivation.Respiration and excretion are basic physiological activities of energy metabolism in animals,and can reflect the physiological status of animals.Changes of environmental conditions(such as salinity) can lead to changes of energy metabolism,which is reflected by changes of oxygen consumption rate,CO2 production rate,ammonia-N excretion rate,O/N ratio,respiratory quotient and C/N ratio etc;2) Osmoregulation organs: gills are very important organs and play a prominent role in osmoregulation and ion transport.Antennal gland also can regulate the osmotic pressure,and maintain the balance of acid-base;3) Ion transport and regulation: including ion transport enzymes(such as Na+-K+-ATPase,V-type H+-ATPase,carbonic anhydrase and HCO3-ATPase),ion transport pathway and neuroendocrine control.Neuroendocrine system could regulate ion transport of epithelial cells in the gill by neurotransmitters releasing signals.Bioamines,cAMP,PKC and CaM have been proved to take part in the regulation of ion transport;4) Haemolymph composition.E.sinensis has the ability to adapt to different salinities by adjusting haemolymph coposition in order to maintain normal life activities.Haemolymph concentration of ion and free amino acids,accompanied by metabolites of blood(such as protein,carbohydrate and lipid) also contribute to haemolymph osmotic pressure;5) Effects of environmental irritants on osmoregulation of E.sinensis.Some environmental irritants(such as heavy metals and toxic substances) could impair osmoregulation.Meanwhile,this paper proposes some suggestions for future research: 1) To strengthen the research on the role and mechanism of antennal gland in osmoregulation;2) To further study the effects of salinity on energy metabolism of E.sinensis;3) The changes of nutrient metabolism(such as amino acid,carbohydrate and lipid metabolism) in the process of osmoregulation need to be further identified;4) To research on the relevant nutrition metabolic enzymes and their functions in osmoregulation of E.sinensis;5) To interpret the molecular mechanism of osmoregulation by molecular biology methods.