Effects of acute heat stress on haemato-biochemical parameters, oxidative resistance ability, and immune responses of hybrid yellow catfish (pelteobagrus fulvidraco × P. vachelli) juveniles

Heat stress induces oxidative stress and weakens the immune system in catfish Clarias magur: Evidence from physiological, histological, and transcriptomic analyses

Climate change is unequivocal, causing a rise in the Earth's temperature, which ultimately impacts all ecosystems. However, aquatic ecosystems are most severely affected by rising temperatures resulting in huge losses to aquaculture industry. The present study investigated the oxidative stress, histopathological changes, and transcriptomic responses in a freshwater catfish Clarias magur subjected to acute heat stress. Fish were exposed to four different temperatures, i.e., 28, 30, 32, and 34 °C, for 96 h to assess their heat tolerance and adaptation behavior. Fish kept at 26 °C were considered the control group. Elevated levels of key antioxidative enzymes such as catalase, glutathione reductase, and superoxide dismutase, were recorded in vital organs (gills, kidney, liver, and rosette). High rates of lipid peroxidation were also observed in the gills, kidney, liver, and rosette. An analysis of the top 25 differentially expressed genes of the gill transcriptome revealed that 72 percent of the transcripts were represented by innate and adaptive immune response genes. Downregulation of BOLA class I and MHC class I molecules indicated impaired immunity whereas, upregulation of MHC class II beta chain and GTPase IMAP8 suggested a compensatory immune response. These findings were also supported by the observed histoarchitectural alterations, such as disintegration of the skin barrier, hepatic and nephrotic apoptosis, tissue hyperplasia, macrophage infiltration, and development of splenic granulomas. This study provides important insights into physiological and molecular mechanisms underlying acute heat stress responses. Understanding these mechanisms is important for developing mitigation strategies to improve the sustainability and resilience of commercially important catfish under continuously changing climatic conditions.

Effects of acute high-temperature on gill tissue structure, serum biochemical indices, antioxidant capacity and liver transcriptomics of Thamnaconus septentrionalis

As global extreme heat events become more frequent, aquaculture faces significant challenges due to prolonged high summer temperatures, which lead to elevated water temperatures. Investigating the physiological and biochemical responses of fish to thermal stress, as well as breeding heat-resistant varieties, are essential strategies for addressing these challenges. Thamnaconus septentrionalis is an important aquaculture species in southern China. When water temperatures exceed 30 °C during the summer, this species experiences reduced feeding, growth stagnation, and increased mortality rates. To elucidate the physiological and biochemical response mechanisms of T. septentrionalis under thermal stress, this study established a high-temperature group (30 °C) and a control group (20 °C) for a 48-h thermal stress experiment. Tissue samples were collected from the experimental fish at 0, 12, 24, and 48 h post-stress. The effects of acute thermal stress on gill tissue structure, serum biochemical indicators, liver antioxidant capacity, and liver transcriptomics were explored. The results revealed that the gill tissues of the high-temperature group exhibited slight bending of the gill filaments, terminal swelling, and cellular vacuolization, along with a tendency for adjacent gill filaments to fuse. The liver antioxidant capacity and serum biochemical indicators in the high-temperature group were significantly elevated compared to the control group (P < 0.05). Transcriptomic sequencing identified 5536 differentially expressed genes (P < 0.05), with 2639 genes upregulated and 2897 downregulated. Gene Ontology (GO) enrichment analysis indicated that differentially expressed genes were primarily associated with metabolic processes and redox reactions. KEGG pathway analysis showed significant enrichment of genes in pathways related to amino acid metabolism, carbon metabolism, and glycolysis/gluconeogenesis, with notable downregulation observed in the high-temperature group. This study provides valuable theoretical insights into the mechanisms underlying the response of T. septentrionalis to high-temperature stress, contributing to the understanding of aquaculture resilience in the face of climate change.

Physiological and oxidative responses of Colossoma macropomum and hybrid ♀ C. macropomum × ♂ Piaractus brachypomus subjected to different stressors in a recirculating aquaculture system (RAS)

The effects of acute handling stress on the physiological and antioxidant responses of tambaqui (Colossoma macropomum) and the hybrid tambatinga (C. macropomum × Piaractus brachypomus) raised in a recirculating aquaculture system were investigated. Thirty juveniles of tambaqui (27.8 ± 2.8 g) and thirty of tambatinga (26.2 ± 3.1 g) were used. Six fish/group were captured and subjected to the sample to determine basal parameters. The remaining animals were chased with hand net for 3 minutes, exposed to air for 2 minutes and subjected to biometry. Blood and oxidative parameters were determined immediately after stress (IAE) and after 1h (1hAE), 24h (24hAE) and 48h (48hAE). Stress caused an increase in the hematocrit of tambaqui at IAE, with reduction after 48hAE. For glycemia, there were differences between the fish groups and collections with higher values for tambatinga and after IAE and 1hAE. Cholesterol in tambaqui increased after 24hAE and 48hAE, decreasing in hybrid after 24hAE with return to basal after 48hAE. SOD increased in IAE while in tambaqui the response only occurred after 48hAE, resulting in an increase in lipid peroxidation. Conclude that biometric management resulted in hemodilution in tambatinga, without recovery of basal parameters. However, the antioxidant system prevented lipid peroxidation.

Transcriptional Rearrangements Associated with Thermal Stress and Preadaptation in Baikal Whitefish (Coregonus baicalensis)

In this work, we describe the transcriptional profiles of preadapted and non-adapted one-month-old juvenile Baikal whitefish after heat shock exposure. Preadapted fish were exposed to a repeated thermal rise of 6 °C above the control temperature every three days throughout their embryonic development. One month after hatching, preadapted and non-adapted larvae were either kept at control temperatures (12 °C) or exposed to an acute thermal stress (TS) of 12 °C above the control temperature. In response to this acute stress, an increase in HSP gene expression (HSP-30, HSP-40, HSP-47, HSP-70, and HSP-90) and TRIM16 was detected, independent of preadaptation. The expression levels of genes responsible for the response to oxygen levels, growth factors and the immune response, HBA, HBB, Myosin VI, Myosin VII, MHC, Plumieribetin, TnI, CYP450, and LDB3 were higher in individuals that had previously undergone adaptation. Genes responsible for the regulation of metabolism, MtCK, aFGF, ARF, CRYGB, and D-DT, however, increased their activity in non-adapted individuals. This information on transcriptional profiles will contribute to further understanding of the mechanisms of adaptation of whitefish to their environment.

Hematological, biochemical and oxidative responses induced by thermal shock in juvenile Tambaqui (Colossoma macropomum) and its hybrid Tambatinga (Colossoma macropomum x Piaractus brachypomus)

The effects of thermal shock on hematological, biochemical and antioxidant responses were evaluated in liver tissue of juvenile tambaqui (Colossoma macropomum) and tambatinga (♀ C. macropomum × ♂ Piaractus brachypomus). Forty juveniles of tambaqui and 40 juveniles of tambatinga, of the same age and with an initial weight of 23.3 ± 6.7 g, were randomly distributed in eight 28L circular tanks. A tank (n = 10 fish) of tambaqui and a tank (n = 10 fish) of tambatinga were then used to obtain basal data. The other animals were subjected to thermal shock with sudden temperature reduction from 28 to 18 ºC. Blood and tissue were then collected after 1, 6 and 24 h from the onset of thermal shock. No mortality was observed during the experimental period. Thermal shock increased triglyceride levels after 24 h of stress for tambaqui and reduced values for tambatinga. There was an effect on plasma glucose only for fish group (P < 0.0001) and collection time (P < 0.0001) with a peak observed for the hybrid after 6 h. The interaction of factors for SOD indicated greater activity for tambatinga at the 6 h collection and lower at basal and 1 h collections. There was an interaction for CAT (P = 0.0020) with less activity for tambatinga at 1 h. However, thermal shock and hybridization did not influence GST and TBARS levels in liver tissue. Therefore, the results suggest that the hybrid, tambatinga, is more efficient at promoting adjustments of biochemical responses and antioxidant enzymes during thermal shock.

Effects of Ocimum basilicum essential oil and ginger extract on serum biochemistry, oxidative stress and gill tissue damage of pearl gentian grouper during simulated live transport

This study explored the effects of the essential oil of Ocimum basilicum (EOOB) and ginger extract (GE) during the transportation of pearl gentian grouper from water quality, serum biochemistry, oxidative stress, meat flavor, and gill tissue morphology. Fish (450 ± 50 g) were allocated to the following 5 treatments: control group (fish transported in water only), 5 mg/LEOOB, 10 mg/LEOOB, 3 mg/LGE, and 6 mg/LGE and transported in insulation boxes (66 × 51 × 37.8 cm) for 72 h. Samples were taken at 0, 12, 36, 60, and 72 h immediately after transport. It was found that 10 mg/LEOOB and 6 mg/LGE could reduce the levels of total ammonia nitrogen (TAN), dissolved oxygen (DO), water pH, serum glucose (GLU), cortisol (COR), liver superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPX), increase the activities of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH), as well as significantly increase the total free amino acid (TFAA) content in muscle compared to the control group (P < 0.05). In addition, by observing the microstructure of gill tissue, it was found that compared with untreated grouper, the morphological damage of gill tissue in EOOB and GE treatment was alleviated. These results indicated that adding appropriate amounts of EOOB and GE to transport water could improve the water quality, relieve stress, and lower energy metabolism of grouper during transport. The results of this research will help to improve the survival rate of grouper after transportation and decrease economic losses to fishery.

Effect of different slaughter/stunning methods on stress response, quality indicators and susceptibility to oxidation of large yellow croaker (Larimichthys crocea)

This study aimed to investigate the effects of different slaughter methods (immersion in ice/water slurry, T1; gill cut, T2; CO2 asphyxia, T3; percussion (hit on the head with a stick), T4; Melissa officinalis L. essential oil + CO2, T5) on physiological stress, oxidative stress, and muscle quality in large yellow croaker. In terms of physiological stress, the levels of glucose (GLU), lactate dehydrogenase (LDH), and catalase (CAT) in CO2 asphyxia samples were significantly lower than those in other samples (p < 0.05). The level of cortisol (COR) in T1 sample was 1.25-1.84 times higher than that of other samples. The GLU level of T1 group was 3.2 times higher than that of T3 sample, and significantly higher than that of other samples. The creatine phosphokinase (CPK) and CAT levels of T2 samples were the highest (2.03 ng/mL and 8.34 U/mL, respectively). Furthermore, the superoxide dismutase (SOD) and glutathione peroxidase (GPx) analysis revealed that T3 and T4 samples could maintain good antioxidant enzyme activity during cold storage. The T3 samples maintained the stability of the protein (the lowest carbonyls and surface hydrophobicity) and reduced lipid oxidation (lower TBARS). In addition, the analysis of pH and water-holding capacity (WHC) revealed that T3 samples had better muscle quality. The muscle of T2 samples kept better color due to bloodletting treatment. The samples obtained after addition of Melissa officinalis L. essential oil had poorer indexes in all aspects compared to the T3 samples, which might be caused by the long anesthesia time of the essential oil.