Immune profiling of rainbow trout (Oncorhynchus mykiss) exposed to Lactococcus garvieae: Evidence in asymptomatic versus symptomatic or vaccinated fish

Changes in blood serum parameters in farmed rainbow trout (Oncorhynchus mykiss) during a piscine lactococcosis outbreak

The aquaculture sector plays a vital role in global food security, yet it grapples with significant challenges posed by infectious diseases. Piscine lactococcosis is one of the significant threats in rainbow trout aquaculture due to its potential to cause severe economic losses through mortalities, reduced growth rates, and increased susceptibility to other pathogens. It poses challenges in disease management strategies, impacting the sustainability and profitability of rainbow trout farming. The current study focuses on the variations in serum blood parameters of farmed rainbow trout Oncorhynchus mykiss during a lactococcosis outbreak caused by Lactococcus garvieae. Blood samples were collected for biochemical analysis, fish were examined for parasites and bacteria, and DNA from bacterial colonies was PCR-amplified and sequenced for identification. Overall, 13 biochemical parameters, including proteins, enzymes, lipids, chemicals, and minerals, were measured in serum blood samples from both diseased and healthy fish. The results indicate significant alterations in the levels of these parameters during the outbreak, highlighting the impact of infections on the blood profile of farmed rainbow trout. Urea levels were significantly higher in diseased fish compared to controls, and creatinine, phosphorus, and magnesium also showed similar trends. Alanine aminotransferase and total protein levels were higher in control fish. Chloride levels differed significantly between groups. Iron levels were higher in controls and lower in diseased fish. No significant differences were found in other parameters. This study reveals significant changes in serum blood parameters of rainbow trout during a lactococcosis outbreak caused by L. garvieae. These changes highlight the potential of these parameters as tools for monitoring health status, stress, and aquaculture management. Continuous monitoring can provide valuable insights into disease severity and overall fish health, aiding in the development of improved management practices. The presented data contribute to understanding the pathophysiology of piscine lactococcosis and developing effective mitigation strategies for farmed rainbow trout.

Pathogenicity of Streptococcus iniae causing mass mortalities of yellow catfish (Tachysurus fulvidraco) and its induced host immune response

The outbreak of mass mortality occurred in Tachysurus fulvidraco farm in Hubei province of China. The pathogenic strain of Streptococcus iniae (termed 2022SI08) was isolated and identified from diseased T. fulvidraco, based on morphological, physiological, and biochemical characteristics, as well as 16S rRNA gene sequence and phylogenetic analysis. Further, the whole genome of isolate S. iniae was sequenced and predicted to contain one single circular chromosome of 1,776,777 bp with a GC content of 37.14%. The genomic sequence analysis showed that 2022SI08 was positive for 204 virulent and 127 antibiotic resistant genes. The experimental challenge demonstrated the high pathogenicity of the retrieved isolate of S. iniae, with a median lethal dosage (LD50) 9.53 × 105 CFU/g. Histopathological examination indicated that the 2022SI08 strain could induce extensive tissue cell degeneration, necrosis, hemorrhage, and inflammation in the skin, gill, fin, spleen, liver, kidney, intestine, eye, and brain. Moreover, the innate immune enzyme activities in serum such as acid phosphatase and alkaline phosphatase were increased significantly at 24 and 48 h post infection (hpi) and then decreased at 168 hpi. The transcriptional profile of immune associated gene in T. fulvidraco following bacterial infection was detected at each point of time, and the results revealed clear transcriptional activation of those genes, which proving their reacting and regulatory role during the response of the host against S. iniae infection. The results revealed that S. iniae was an etiological agent in the mass mortalities of T. fulvidraco and this research will be conducive for increasing our understanding on pathogenesis and host defensive system in S. iniae invasion.

Ecotoxicological effects of cypermethrin on indigenous climbing perch (Anabas testudineus)

Pesticides including cypermethrin (10% EC) are commonly used pesticide in tea gardens of Bangladesh possess distinct harmful effects on an aquatic community. The experiment was carried out to assess the ecotoxicological effects of cypermethrin (10%) concentrate on indigenous Climbing Perch (Anabas testudineus). A total of 120 A. testudineus (mean length 16 ± 2.67 cm and mean weight 31.6 ± 3.56 g) were exposed to the acute toxicity test when the lethal concentration 50 value (LC50) for 96 h was maintained at 1.00 ppm. Three different sub-lethal concentrations of 0.05 ppm (5%), 0.10 ppm (10%), and 0.20 ppm (20%) were used respectively as three treatments and a control of 0 ppm with three replicates each. Restlessness, erratic movement, increased opercular activities, loss of equilibrium, and irregular response to feeding were observed in all the treatments compared to control one. Concerning histopathological alterations, all the analyzed organs showed highest changes in the T3 (cypermethrin conc. 20%) compared to other treatments while T0 (0 ppm) had normal structure. The major changes in the gill were epithelial cell hyperplasia, necrosis, severe lamellar fusion and epithelial lifting; while necrotic proximal tubules, glomerular shrinkage, disrupted renal corpuscle of the kidney and nuclear pyknosis, degenerated hepatic cells and vacuolation were observed in the liver. Severe melanomacrophage centre (MMC), haemosiderosis and vacuolation were found in spleen. The effect of cypermethrin on the hematological parameters of experimental fish was also studied. Red blood cells, hemoglobin and hematocrit were decreased in the experimental groups and lowest value was in T3 while values of white blood cells were increased in the experimental groups compared to control one. Hence, the present observation revealed that pesticides even at low concentrations can cause harmful effects on A. testudineus.

Chitosan Microparticles Enhance the Intestinal Release and Immune Response of an Immune Stimulant Peptide in Oncorhynchus mykiss

The aquaculture industry is constantly increasing its fish production to provide enough products to maintain fish consumption worldwide. However, the increased production generates susceptibility to infectious diseases that cause losses of millions of dollars to the industry. Conventional treatments are based on antibiotics and antivirals to reduce the incidence of pathogens, but they have disadvantages, such as antibiotic resistance generation, antibiotic residues in fish, and environmental damage. Instead, functional foods with active compounds, especially antimicrobial peptides that allow the generation of prophylaxis against infections, provide an interesting alternative, but protection against gastric degradation is challenging. In this study, we evaluated a new immunomodulatory recombinant peptide, CATH-FLA, which is encapsulated in chitosan microparticles to avoid gastric degradation. The microparticles were prepared using a spray drying method. The peptide release from the microparticles was evaluated at gastric and intestinal pH, both in vitro and in vivo. Finally, the biological activity of the formulation was evaluated by measuring the expression of il-1β, il-8, ifn-γ, Ifn-α, and mx1 in the head kidney and intestinal tissues of rainbow trout (Oncorhynchus mykiss). The results showed that the chitosan microparticles protect the CATH-FLA recombinant peptide from gastric degradation, allowing its release in the intestinal portion of rainbow trout. The microparticle-protected CATH-FLA recombinant peptide increased the expression of il-1β, il-8, ifn-γ, ifn-α, and mx1 in the head kidney and intestine and improved the antiprotease activity in rainbow trout. These results suggest that the chitosan microparticle/CATH-FLA recombinant peptide could be a potential prophylactic alternative to conventional antibiotics for the treatment of infectious diseases in aquaculture.