Effect of hyper or hypo-osmotic conditions on neutral amino acid uptake and oxidation in tissues of the crab Chasmagnathus granulata

Nutrition and Functions of Amino Acids in Aquatic Crustaceans

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H₂S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

Molecular insights into information processing and developmental and immune regulation of Eriocheir sinensis megalopa under hyposaline stress

Eriocheir sinensis is an important euryhaline catadromous crustacean of the Yangtze River and an important commercial species for breeding in China. However, wild E. sinensis have suffered serious damage attributed to overfishing, climate change, etc. The Ministry of Agriculture of China issued a notice banning the commercial fishing of wild E. sinensis. E. sinensis megalopa migrates upriver into fresh water for growth and fattening, which creates optimal conditions to experimentally explore its hyposaline osmoregulation mechanism. We performed comparative transcriptome analyses of E. sinensis megalopae under hyposaline stress. The results suggest that KEGG pathways and genes related to genetic information processing, developmental regulation, immune and anti-stress responses were differentially expressed. The present study reveals the most significantly enriched pathways and functional gene groups, and explores the hyposaline osmoregulation mode of E. sinensis megalopae. This study lays a theoretical foundation for further studies on the osmoregulation and developmental mechanisms of E. sinensis.

Identification of potential markers and sensitive tissues for low or high salinity stress in an intertidal mud crab (Macrophthalmus japonicus)

Macrophthalmus japonicus is an intertidal mud crab is an ecologically important species in Korea, can tolerate a wide range of natural and anthropogenic stressors. Environmental changes especially salinity cause physiological stress to the marine habitats. Differential gene transcription of M. japonicus tissues provided information about tissue specific responses against salinity. Five potential genes were identified and their transcription levels were determined quantitatively comparison to seawater (SW: 31 ± 1 psu) in M. japonicus gills and hepatopancreas after exposed them to different salinities. Ecdysteroid receptor (Mj-EcR), trypsin (Mj-Tryp), arginine kinase (Mj-AK), lipopolysaccharide and β-1,3-glucan binding protein (Mj-LGBP) and peroxinectin (Mj-Prx) in hepatopancreas up-regulated against different salinities. In contrast, the gills, Mj-EcR, Mj-Tryp and Mj-AK showed late up-regulated responses to 40 psu compared to SW. All genes except Mj-LGBP showed up regulation in the gills as time dependent manner. These genes can be considered as potential markers to assess responses in salinity changes. This study suggests hepatopancreas is a suitable tissue for transcriptional, biochemical and physiological responses analysis on M. japonicus in low and high salinity stress.

Identification and characterization of differentially expressed transcripts in the gills of freshwater prawn (Macrobrachium rosenbergii) under salt stress

The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important species. It is a euryhaline shrimp, surviving in wide-range salinity conditions. A change in gene expression has been suggested as an important component for stress management. To better understand the osmoregulatory mechanisms mediated by the gill, a subtractive and suppressive hybridization (SSH) tool was used to identify expressed transcripts linked to adaptations in saline water. A total of 117 transcripts represented potentially expressed under salinity conditions. BLAST analysis identified 22% as known genes, 9% as uncharacterized showing homologous to unannotated ESTs, and 69% as unknown sequences. All the identified known genes representing broad spectrum of biological pathways were particularly linked to stress tolerance including salinity tolerance. Expression analysis of 10 known genes and 7 unknown/uncharacterized genes suggested their upregulation in the gills of prawn exposed to saline water as compared to control indicating that these are likely to be associated with salinity acclimation. Rapid amplification of cDNA ends (RACE) was used for obtaining full-length cDNA of MRSW-40 clone that was highly upregulated during salt exposure. The sequenced ESTs presented here will have potential implications for future understanding about salinity acclimation and/or tolerance of the prawn.