Histopathological alterations study in cultured tilapia from South Mexican as a diagnostic tool in aquaculture monitoring health

Several studies have been conducted in the last 3 years to evaluate tilapia’s parasitic and bacterial infection in cultures in Mexico. The present work evaluates the severity, prevalence, and health condition through the histopathological index based on the damage in the organs and tissues of tilapia cultured in ponds and cages during 2018 and 2019. Seven hundred and eight fish were collected from ponds and cages of tilapia farms in Chiapas, Oaxaca, and Guerrero and preserved and processed for histological observations. The prevalence of histopathological alterations found in each biological system was calculated and expressed in percentage. The histopathological index of each fish (HI fish ) was calculated based on two different semi-quantitative methods. Histologically, the tilapia showed alterations as inflammation, melanomacrophage centers, hyperplasia, telangiectasias, and epitheliocystis unrelated to specific infectious pathogenic agents in both years but suggest effects associated with diverse factors in different biological systems. The prevalence was higher in all the parameters evaluated in 2018. The pathological manifestations in both years show that the health condition of the fish was affected regardless of the type of culture (cages and ponds), with the respiratory and digestive systems the most affected. These results show a baseline of the health condition of the tilapias cultured in southeast Mexico. The observed damages were not lethal but reflected a constant exposition to stressful conditions to trigger chronic inflammatory responses in the fish and make them susceptible to pathogens present in the environment.