Hybrid red tilapia Pargo-UNAM and gray tilapia Oreochromis niloticus display different susceptibility and immune response against Aeromonas veronii infection
The red tilapia synthetic population Pargo-UNAM is an important aquaculture resource in Mexico. It is primarily cultivated in the southeastern region of the country, although it is also present in most states that produce tilapia. One of the main challenges that the aquaculture of tilapia culture faces is the occurrence of infectious diseases, particularly those caused by bacterial pathogens. In this respect, a common bacterial disease present in the aquaculture of tilapia is septicemia caused by different species of the genus Aeromonas, which provokes mass mortalities and has developed antimicrobial resistance, limiting treatment options. One of the strategies to reduce disease susceptibility is fish hybridization; however, evidence indicates this can jeopardize population survival by accelerating the loss of gene diversity, affecting various fitness-related traits, including immune response. In the present study, i) Aeromonas veronii was identified as the cause of cumulative mortalities in red hybrid tilapia Pargo-UNAM during a natural infection. Then, ii) the differential survival rate to A. veronii infection of hybrid red tilapia Pargo-UNAM and gray tilapia Oreochromis niloticus was assessed, where the red hybrid was more susceptible than the gray O. niloticus. Finally, iii) the transcriptional changes induced in the spleen of the organisms during the infection were studied to identify at the molecular level the cause of the different responses between both tilapia variants. Results showed that O. niloticus displays a higher number of genes related to external stimuli and bacterial response than Pargo-UNAM. Evaluation of disease susceptibility among tilapia variants represents a strategy to control disease presentation and dissemination.