Hematological alterations and bacterial abundance of Edwardsiella tarda in catfish (Clarias Sp.) cohabiting with carrier silver rasbora (Rasbora argyrotaenia)

Background: Catfish farming is often performed with high stocking densities, which can result in environmental degradation, stress, and increased vulnerability to infections such as Edwardsiellosis caused by Edwardsiella tarda. Infection by E. tarda occurs through horizontal transmission during cohabitation between infected and healthy fish. Aim: This study aimed to investigate hematological alterations and abundance of E. tarda in catfish following cohabitation with carrier silver rasbora. Methods: A total of 160 silver rasboras (length: 6.02 ± 0.36 cm, weight: 2.065 ± 0.565 g) were immersed in an E. tarda suspension at a concentration of 10 13 colony forming unit (CFU) /ml for 2 weeks. Subsequently, they were cohabitate with 240 catfish (length: 6.9 ± 2.35 cm, weight: 2.78 ± 1.37 g) at different density ratios: 1:1 (P1), 1:2 (P2), and 2:1 (P3), along with negative control (without E. tarda, NC), and with E. tarda at 1013 CFU/ml (positive control) for 5 days. The observed parameters included hematological profiles (total erythrocytes, leukocytes, hemoglobin (Hb) levels, and leukocyte differentials) and the density of E. tarda in various organs (liver, kidneys, and spleen). Results: Catfish cohabiting with E. tarda-infected silver rasbora exhibited significant hematological alterations, including elevated percentages of neutrophils, lymphocytes, and monocytes, alongside decreased erythrocyte counts, Hb levels, and total leukocyte counts. Furthermore, the highest density of E. tarda was detected in the liver (1.15 ± 0.11 × 10 4 CFU/ml) compared with the other organs. Conclusion: Cohabitation between healthy catfish and E. tarda carrier silver rasbora resulted in bacterial infection in the catfish.