Figure 15.

Histological findings in the organs of red tilapia post-challenge with Streptococcus iniae (A,B) and Aeromonas hydrophila (C,D), respectively. (A) Brain tissues of unvaccinated fish showing severely congested blood vessels surrounded by mononuclear inflammatory cells and empty space (arrowhead); (B) tubular degeneration (star), mononuclear cell infiltration (thin arrow), and a necrotic area between the renal tubules (thick arrow) in the kidney tissues of unvaccinated fish; (C) spleen tissue showing severe necrosis and depletion of lymphocytes (thick arrow), presence of hemosiderosis (arrowhead), hemorrhage (star), and huge accumulation of melanomacrophage centers (thin arrow) in unvaccinated fish; and (D) liver tissue from the unvaccinated fish showing marked necrosis of hepatocytes (thick arrow) and pancreatic cells (star), along with diffuse vacuolation (arrowhead). H & E, 100X.