Impacts of circadian rhythm and melatonin on the specific activities of immune and antioxidant enzymes of the Chinese mitten crab (Eriocheir sinensis).

Many physiological functions of crustaceans show a rhythmic change to adapt to daily environmental cycles. However, daily variation in the immune and antioxidant status and its possible correlation with circulatory melatonin levels during the daily cycle have not been reported in the Chinese mitten crab, Eriocheir sinensis. In this study, the specific activities of immune and antioxidant enzymes of E. sinensis during the 24 h cycle and its relationship with injected doses of melatonin were evaluated. The results showed that the immune parameters in the hemolymph, such as total hemolymph count, alkaline phosphatase, lysozyme, acid phosphatase, and phenol oxidase, exhibited bimodal patterns during the 24 h cycle, these parameters were synchronized with the activity of antioxidant enzymes such as malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase, and catalase. However, there was only one peak in the muscle (during 1200-1600 h) and gills (during 0400-0800 h). The survival rate reached approximately 80% in 5 days when melatonin concentrations were lower than 0.05 g/L, significantly decreasing as melatonin concentrations increased. Four hours after melatonin injection, MDA levels in the muscle and hemolymph were significantly lower than those in the control group. Eight hours after melatonin injection, SOD levels in the hemolymph were significantly higher than those in the control group. These findings highlight the importance of considering circadian regulation of innate immunity when comparing immune responses at fixed times.

Comparative transcriptome analysis provides insights into the molecular basis of circadian cycle regulation in Eriocheir sinensis.

The eyestalks of crustaceans play an essential role in controlling a variety of physiological functions by converting light into hormonal signals. To obtain a more complete description of eyestalk biology in the commercially important Chinese mitten crab (Eriocheir sinensis), we conducted comparative transcriptome analysis of eyestalks during the day and at night using high-throughput sequencing on an Illumina HiSeq 4000 platform. We obtained 47,092 unigenes-including 4771 differentially expressed genes (DEGs)-from eyestalks during the day and at night. We found that 4269 DEGs were upregulated during the day and 502 DEGs were upregulated at night. We identified five DEGs that may contribute to molting, including molt-inhibiting hormone, cuticle, catalase, aquaporin, and ubiquitin-conjugating enzyme; hence, similar to other crustaceans, Eriocheir sinensis may molt at night. We further identified eight DEGs related to behavior regulation, including three glutamate dehydrogenase genes that were upregulated during the day. Thus, changes in the eyestalks may partially compensate for daily changes in illumination in the Chinese mitten crab's normal environment. Our present study is the first genome-wide transcriptome analysis of the eyestalks of Eriocheir sinensis during the day and at night. Our findings provide a valuable insight into the molecular basis of circadian cycle regulation in crustaceans.

Comparative transcriptome analysis of Chinese grass shrimp (Palaemonetes sinensis) infected with isopod parasite Tachaea chinensis.

Parasitic isopods negatively affect reproduction and ingestion in several commercially important crustaceans; however, little is known about such parasite-host interactions. Therefore, we performed high-throughput sequencing of cDNA samples from Chinese grass shrimp Palaemonetes sinensis infected by parasitic isopod Tachaea chinensis and a non-infected control. We randomly assembled 46,858,882 and 41,110,746 clean reads from the parasitized and control groups, respectively. From these, we identified 1323 differentially expressed genes (DEGs) (p < 0.05), of which 702 were up-regulated and 621 were down-regulated after T. chinensis infection, respectively. The up-regulated genes were enriched in 'ribosome', 'purine metabolism', and 'pyrimidine metabolism' signalling pathways, suggesting altered host nucleotide metabolite levels, possibly through the action of intracellular parasites transported by T. chinensis. Additionally, 14 representative DEGs involved in reproduction were down-regulated after parasitisation, indicating T. chinensis causes cascading effects in P. sinensis. Overall, parasitisation appeared to affect host immune response, metabolism, and gonadal development. In conclusion, the present study improves our understanding on the molecular mechanisms underlying interactions between isopod parasites and their crustacean hosts.

Anaesthetic Effects of Eugenol on Grass Shrimp (Palaemonetes sinensis) of Different Sizes at Different Concentrations and Temperatures.

Essential oil derivatives are widely used for anaesthetising aquatic animals. However, the effectiveness of anaesthesia often varies according to the anaesthetic agent, species, temperature, dosage, and interactions among these factors. This study evaluated the effects of eugenol on three sizes of the shrimp Palaemonetes sinensis at different concentrations and temperatures. Eugenol dose, water temperature, and shrimp size were found to significantly influence anaesthesia in P. sinensis. Induction time decreased linearly with increasing water temperature and eugenol concentration, while it increased with body weight. However, recovery times lengthened with increasing concentration and temperature, and shortened with lower body size. At 100 and 200 µL/L eugenol concentrations, the survival rates of medium and large shrimps were maintained at over 80% at all temperatures studied over 72 h recovery. However, the survival rates of small shrimps were below 60% at 24 °C and 28 °C over 5 days of recovery. These results suggest that eugenol is an effective and rapid anaesthetic for P. sinensis, but it might have disadvantages such as slow recovery and possible mortality in small shrimps and at higher temperatures and dosages.