Effects of Photoperiod on Survival, Growth, Physiological, and Biochemical Indices of Redclaw Crayfish (Cherax quadricarinatus) Juveniles

Through a 30-day experiment, this study investigated the effects of five photoperiods (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) on the survival, enzyme activity, body color, and growth-related gene expression of redclaw crayfish (Cherax quadricarinatus) juveniles. The results showed that C. quadricarinatus juveniles under 18L:6D and 24L:0D photoperiods exhibited the highest survival rate, which was significantly higher than the survival rates of juveniles under the other three photoperiods (p < 0.05). However, the 0L:24D group had the highest final body weight and weight gain rate, significantly surpassing those of the 12L:12D, 18L:6D, and 24L:0D groups (p < 0.05). Regarding enzyme activity and hormone levels, juveniles under the 18L:6D photoperiod exhibited relatively higher activity of superoxide dismutase (SOD), acid phosphatase (ACP), and lysozyme (LZM) enzymes than those under other photoperiods, but their levels of melatonin and cortisol were relatively low. In addition, the 24L:0D group showed the highest malondialdehyde (MDA) content. Analysis of gene expression levels revealed that retinoid X receptor (RXR) and α-amylase (α-AMY) genes in C. quadricarinatus juveniles exhibited significantly higher expression levels under the 18L:6D photoperiod than those under the other four photoperiods (p < 0.05). With increasing daylight exposure, the body color of C. quadricarinatus changed from pale blue to yellow-brown. In summary, C. quadricarinatus juveniles achieved high survival rates, good growth performance, strong antioxidant stress response, and immune defense capabilities under an 18 h photoperiod. Therefore, in the industrial seedling cultivation of redclaw crayfish, it is recommended to provide 18 h of daily light. Further, the study demonstrated the ability to manipulate the body color of C. quadricarinatus through controlled artificial photoperiods. These findings provide essential technical parameters needed for the industrial cultivation of C. quadricarinatus juveniles.

Evaluation of Microplastics and Microcystin-LR Effect for Asian Clams (Corbicula fluminea) by a Metabolomics Approach

Microplastics (MP) and microcystins (MCs) are two co-occurring pollutants in freshwater ecosystems that pose significant risks to aquatic organisms and human health. This study investigates the interactions between MP and MCs and their effects on the metabolic responses of freshwater aquaculture. Asian clams have been used as an indicator of microplastic pollution in freshwater ecosystems. The present study investigates metabolic responses of Asian clams during microplastic and microcystin-LR stress to identify health impacts and elucidate mechanistic effects of external stressors on Asian clams. A liquid chromatography/mass spectrometry (LC-MS)-based metabolomics approach was used to identify metabolic perturbations and histological section technique was used to assess changes of tissues from different Asian clam treatment groups. The results showed significantly pathological changes in the gills and hepatopancreas in experimental clam compared to control (healthy) clam. Metabolomics revealed alterations of many metabolites in the hepatopancreas of six Asian clam comparison groups, reflecting perturbations in several molecular pathways, including energy metabolism, amino acid metabolism, protein degradation/tissue damage, and oxidative stress. Overall, this study emphasizes the importance of understanding the interactions between MP and MCs and the need for proactive measures to safeguard freshwater ecosystems and human health.

Effects of Clostridium butyricum on Intestinal Microflora and Metabolism of Eriocheir sinensis

Clostridium butyricum, a new probiotic in recent years, can produce butyric acid and short-chain fatty acids. It has the characteristics of strong acid and alkali resistance, high temperature resistance, and strong resistance to most antibiotics, and has more advantages than other probiotics. However, the action mechanism of C. butyricum on Eriocheir sinensis is still unclear and needs further study. In this study, when C. butyricum was added to the basic diet, the number of living bacteria was 0, 1 × 106 and 1 × 108 CFU/g, respectively. The E. sinensis were randomly divided into three groups: (blank control group, experimental group 1 (1 × 106 CFU/g) and experimental group 2 (1 × 108 CFU/g)). They were fed an experimental diet for 28 days. The effects of C. butyricum on E. sinensis were studied by detecting the differences in non-specific immune indexes, intestinal microflora, and metabolites between serum and hepatopancreas. The results showed that C. butyricum could improve the antioxidant ability of E. sinensis serum and hepatopancreas, protect intestinal tissues, and promote the absorption of nutrients. At the same time, it can enhance the microbial diversity and richness of the E. sinensis gut flora. LC-MS metabolomics was used to detect the metabolism of intestinal flora. It was found that C. butyricum could up-regulate lysophosphatidylcholine in the intestine. Through the KEGG enrichment pathway, it was found that significantly different metabolites were mainly concentrated in six metabolic pathways. The purine metabolism and alanine, aspartate, and glutamate metabolism pathways showed a downward trend, indicating that the addition of C. butyricum to feed could reduce purine metabolism, promote the water-salt balance of the organism's cells, and reduce inflammation. In this study, it was found that the addition of certain concentrations of C. butyricum to feed could improve the antioxidant ability of E. sinensis, improve the intestinal flora environment, and promote the growth of beneficial bacteria in the gut. This can promote the body's metabolism, which is more conducive to its growth.