RESUMEN
Flavobacterium covae (columnaris) is the most detrimental bacterial disease affecting the largemouth bass (Micropterus salmoides Lacépède) aquaculture industry. In the current study, fish received an intraperitoneal injection of either 1× PBS (100 µL), LPS in PBS (100 µL, 10 µg/mL), or F. covae (100 µL, 2.85 × 1011 CFU/mL) to simulate immunological challenges. After 24 h post-injection, liver tissue from the control and treated groups were then collected for transcriptome analysis. Results of the Gene Ontology (GO) and KEGG pathway analyses for the F. covae and LPS-injected groups found differentially expressed genes (DEGs) enriched primarily in toll-like receptors (TLRs), cytokine-cytokine receptors, complement and coagulation cascades, and the PPAR signalling pathways. This suggests that the liver immune system is enhanced by these five combined pathways. Additionally, the DEGs TLR5, MYD88, and IL-1 were significantly upregulated in F. covae and LPS-injected fish compared to the controls, whereas IL-8 was downregulated. The upregulation of TLR5 was unexpected as F. covae lacks flagellin, the protein that binds to TLR5. Additionally, it is unknown whether the TLR5 is upregulated by LPS. Further research into the upregulation of TLR5 is warranted. These results provide insight into immune responses and associated pathways contributing to the immune system in the liver during columnaris infection and induced response to LPS in largemouth bass.
RESUMEN
Flavobacterium covae (columnaris) is a microbial pathogen of the Golden Shiner (Notemigonus crysoleucas), a principal bait species. We investigated the effects of density and water temperature on the survival of fish subjected to a columnaris challenge and whether flow cytometry (FCM) could be a fast and reliable method to distinguish and enumerate F. covae populations from water and fish in experimental tanks. Juvenile Golden Shiners averaging 2.62 (±0.78 S.D.) g (negative for F. covae) were used in simultaneous trials at 22°C and 28°C in two ultra-low flow-through systems: each consisting of four treatments and five replicates per treatment. Treatments were fish stocked at either 600 fish/m3 or 2,400 fish/m3 and either challenged with F. covae or not; survival was observed for 48 h after challenge. Samples of water and fish tissue were obtained for FCM enumerations and validation by qPCR. No significant differences in survival were recorded between density treatments; however, high temperature and columnaris challenge treatments showed significantly higher mortality. Bacterial enumeration (number/mL) by FCM highly correlated with bacterial counts r = 0.81 (p = 0.001) in the water samples. Higher water temperatures may have increased columnaris infections and mortality in Golden Shiners. Flow cytometry is a reliable method of enumerating F. covae from experimental tank water samples.
RESUMEN
Split-pond systems (SPS) such as those used for catfish are being considered for raising baitfish. When using these systems for baitfish such as golden shiners Notemigonus crysoleucas, an important factor to be considered is how well the species can tolerate crowding, as the design mandates fish be confined to a smaller portion of the pond. Another aspect of the SPS design is the water flow between the two units for at least 10-14 h each day. SPS can be successfully implemented for other species if factors such as crowding, and water flow do not affect growth. Two laboratory studies were conducted each using 12, 40-L tank flow-through system to observe the growth and physiological performance of golden shiners held for 28 days at three crowding densities: 600; 1,200, and 2,400 fish/m3, keeping water flow at 1 cm/s (Experiment 1) and using three flow rates: 1, 2, and 4 cm/s at similar densities (600 fish/m3) (Experiment 2). At the end of the experiments, fish were subject to acute 1-min confinement stress and whole-body cortisol was measured at 30 min intervals for up to 2 h to monitor the secretion pattern and recovery. Results from experiments showed no difference in the final weight, length, feed conversion, and survival among treatment groups; survival rates were lower in the flow study because of columnaris Flavobacterium covae infections. Baseline cortisol was also not different among the treatments. Cortisol increased 30 min after the acute stress and returned to near baseline in 2 h in the crowding study suggesting acclimation to the chronic stressor. However, in the flow study, cortisol remained elevated even after 2 h, and hence a compromised pathophysiological response. Crowding and water flow do not impair feed intake, growth, or survival in golden shiners, and in these aspects may be a suitable species for SPS.