Mitigating effects of seaweed on gene expression and histological damage in Nile tilapia under acute ammonia stress and bacterial infection

Ammonia exposure can be considered more stressful for aquatic animals when it is concurrent with bacterial infection. In this regard, the study was planned to evaluate ammonia stress, the Aeromonas hydrophila infection, and their synergic effect on Nile tilapia to understand this interaction and the inclusion of seaweed extract (ASE), a natural agent for rearing water to reduce these negative influences. Seven groups of fish with the same initial weight were allocated as the control group: T0 (free of ammonia, A. hydrophila, and ASE), fish exposed to ammonia (2.5 mg/L), A. hydrophila stress, concurrent ammonia, and A. hydrophila stress without ASE (T1–T3) while groups (T4–T6) treated with ASE respectively. Data illuminated that an adverse effect on haemato-biochemical and immunological indices was seen in fish exposed to ammonia and A. hydrophila stress separately or together, and these indices improved after being treated with ASE, particularly in T4 and T5 fish groups. Likewise, antioxidant activity significantly decreased (SOD and CAT) along with increased MDA levels in fish subjected to the stress of ammonia and A. hydrophila separately or together without ASE while improved in these indices after being treated with ASE, especially in T4 and T5 fish groups. The expressions of TNF-α, HSP70, LZM, COX-2, C3, IL-1β, and IL-8 genes were downregulated in ASE-treated fish and upregulated in fish subjected to ammonia and A. hydrophila infection separately or together. Conversely, SOD CAT and IL-10 gene expression were elevated in ASE-treated fish (T3–T6) and declined in fish subjected to ammonia and A. hydrophila infection separately or together (T1-T3). The histopathology analysis showed that fish subjected to ammonia and bacterial infection displayed inflammatory and irregular characteristics, while fish treated with ASE induced anti-inflammation effects. Hence, the study concluded that ammonia increases the infection of A. hydrophila, and treated with AES protects Nile tilapia from these stresses.