Toxicity of common biocides used in aquaculture to embryos and larvae of Brachymystax tsinlingensis Li

Surviving the heat: The homeostatic regulation mechanism of endangered Brachymystax tsinlingensis

Conservation and utilization of Brachymystax tsinlingensis Li, 1966 (B. tsinlingensis), an endangered cold-water fish, is severely hampered by heat stress. In this study, heat stress and recovery experiments were firstly performed and implied that the intestine of B. tsinlingensis remained capable of self-regulation under heat stress. Therefore, transcriptome analysis was used to investigate the homeostatic mechanisms of B. tsinlingensis during temperature fluctuations. The results showed that a total of 5775 differentially expressed genes (DEGs) (1725 up- and 4050 down-regulated) were identified in the heat stress group, and 4312 DEGs (2024 up- and 2228 down-regulated) were identified in the recovery group when compared to their expression levels in the control group. Through Gene Set Enrichment Analysis (GSEA), citrate cycle (TCA cycle), oxidative phosphorylation, apoptosis, ferroptosis, focal adhesion, and tight junction pathways were found to be significantly up-regulated during heat stress, and declined during the recovery process. The results illustrated that heat stress caused ferroptosis and apoptosis in B. tsinlingensis. However, the organism was able to maintain homeostasis during temperature fluctuations modulating its energy metabolism, as well as the barrier and immune functions of the intestine. These findings help to enhance our understanding of the acclimation mechanisms of cold-water fish in present-day climate change.

Intestinal Tissue, Digestive Enzyme, and Antioxidant Enzyme Activities in the Early Development Stage of Endangered Brachymystax tsinlingensis

This work explores the digestive system characteristics of Brachymystax tsinlingensis during early developmental stages and aims to solve the problem of high lethality of fry during the transgression period, which is crucial for the artificial propagation and population conservation of endangered fishes. This study was carried out on intestinal tissue, digestive enzymes, and antioxidant enzyme activities in the early development stage of Brachymystax tsinlingensis. Ten random samples during endogenous nutrition (7, 10, and 11 days after hatching), mixed nutrition (13 and 19 DAH), and exogenous nutrition (31, 33, 39, 45, and 73 DAH) were collected by histological and biochemical analysis methods. The results showed that the intestine of Brachymystax tsinlingensis already has four layers initially at 7 DAH, and the intestinal gland tissue is evident at 73 DAH. The contents of total protein (TP) and the activities of lipase (LPS) and trypsin (TPS) were maximal at 39 DAH, and the activities were 3.20 ± 0.26 mg/mL, 2.52 ± 0.69 U/g, and 2717.45 ± 295.26 U/mg, respectively. Catalase (CAT) and glutathione peroxidase (GSH-PX) activities both showed the lowest values at 39 DAH, which were 0.57 ± 0.11 U/mg and 3.35 ± 0.94 U/mg, respectively. The activity of amylase (AMS) and the content of malonaldehyde (MDA) increased, and the highest values were reached at 45 DAH (1.32 ± 0.41 U/mg) and 73 DAH (1.29 ± 0.43 nmoL/mg), respectively. Superoxide dismutase (SOD) and GSH-PX activities both showed a peak value at 7 DAH (126.58 ± 20.13 U/mg and 6.47 ± 1.86 U/mg). Overall, the changes in intestinal tissue, digestive enzymes, and antioxidant enzyme activities at 39 DAH of Brachymystax tsinlingensis are inseparable from different vegetative stages during the developmental period, and these results can provide a reference for the proliferation and cultivation of Brachymystax tsinlingensis resources.