Intraperitoneal injection of Chaetomorpha aerea extract boosted immunocompetence, antioxidant status and disease resistance against Aeromonas hydrophila in grey mullet, Mugil cephalus juveniles.

The current research was conducted to examine the effects of intraperitoneal injection (IP) of hot water extract of Chaetomorpha aerea (HWECA) on some physiological responses and disease resistance against Aeromonas hydrophila infection in flathead grey mullet, Mugil cephalus (initial body mass 25 ± 0.5 g) juveniles. Six experimental groups, each containing triplicates (n = 30 fish/tank) were designed. A positive control and a negative control group received an injection of phosphate buffered saline (PBS) without HWECA. The treatment groups were administered with HWECA at 25 (HWECA25), 50 (HWECA50), 100 (HWECA100), and 200 (HWECA200) mg/kg. After a week, all experimental groups, except the positive control, were challenged with Aeromonas hydrophila (1 × 107 cells/mL). The positive control group was solely injected with PBS. Growth performance and feed utilization improved in the HWECA-treated groups (P < 0.05). Treatment with the 100 mg/kg HWECA resulted in a significant decline in serum alanine and aspartate aminotransferases activities and concentration of serum glucose and cortisol compared to the negative control group (P < 0.05). The liver superoxide dismutase and catalase activities were significantly higher in the HWECA100 group, meanwhile malondialdehyde content decreased in this group (P < 0.05). Serum total protein level, phagocytic, respiratory burst and lysozyme activities were found to be markedly higher in the HWECA100 compared to the negative control (P < 0.05). The cumulative mortality increased to 75% in the negative control group, in contrast to mortality rates of 20 and 25% noticed in the HWECA100 and HWECA200 groups, respectively. Remarkably, the liver histopathological examination revealed that fish infected with A. hydrophila exhibited inflammatory and abnormal traits, whereas those treated with HWECA showed anti-inflammatory effects. These results showed that IP administration of 100 mg/kg HWECA could be a beneficial phytobiotic to boost antioxidant status, immunocompetence and disease resistance in M. cephalus against A. hydrophila infection.