Lactococcosis is a serious bacterial infection that impacts both freshwater and marine fish species, known for its swift development and elevated mortality rates. The increasing prevalence of Lactococcus petauri infections in aquaculture poses significant challenges to rainbow trout health and production. Understanding the impact of this infection on serum parameters is crucial to understand the disease pathogenesis and for developing effective management strategies.
A total of 33 resistant (R) and 33 susceptible (S) rainbow trout individuals, weighing 450 ± 212.13 g, were anesthetized and injected intracoelomically with L. petauri (TURK72 strain) at a dose of 1×105 CFU/fish in 0.3 mL saline. Five S and five R individuals/time point were euthanized with MS-222 for blood and serum sampling, in accordance with current regulations (Legislative Decree No. 26/2014, which implements Directive 2010/63/EU, with permission for ethical statements No. 1012/2023-PR). Serum analyses were conducted at three different time points (T1-T4), comparing the results to baseline values (T0) as the pre-inoculation control. The analyses focused on total proteins, albumin, enzymes, lipids, metabolites, and minerals, while monitoring for mortalities was conducted.
Descriptive analysis of blood biochemical parameters in rainbow trout revealed variability across groups and time points. Urea levels ranged from 7 mg/dL (T4_S) to 10 mg/dL, while creatinine remained stable (0.14-1.09 mg/dL). Cholesterol and triglycerides exhibited significant variability, with cholesterol levels between 145 mg/dL (T1_S) and 624 mg/dL (T2_S), and triglycerides from 95 mg/dL (T1_S) to 640 mg/dL (T3_R). Significant fluctuations were observed in alanine aminotransferase (ALT) and alkaline phosphatase, particularly at T1. Particularly, phosphorus levels were significantly different in the resistant group at T1 (p<0.05), and total protein levels were higher in the resistant group at T1 (p<0.05). Iron levels increased significantly in both groups at T1 (p<0.05 for S, p<0.01 for R), indicating a differential response to L. petauri infection. Overall, certain biochemical parameters displayed significant changes post-infection, reflecting the varying responses between R and S trout.
The biochemical responses of rainbow trout to L. petauri infection indicate that specific parameters, such as phosphorus, ALT, calcium, and chloride, vary significantly between resistant and susceptible groups. These results highlight the potential of these biochemical markers for monitoring health status and responses to infection in farmed rainbow trout.