A liquid seaweed extract (TAM®) improves aqueous rearing environment, diversity of zooplankton community, whilst enhancing growth and immune response of Nile tilapia, Oreochromis niloticus, challenged by Aeromonas hydrophila

Abstract

A commercial seaweed liquid extract (TrueAlgaeMax, TAM®), previously showed a high content of phytochemical compounds and resulted in promoting growth and immune response of Nile tilapia, when applied as dietary supplementation. In the current study, the effects of applying TAM® as a natural agent to rearing water on growth performance, feed utilization, and immune response of Nile tilapia, Oreochromis niloticus, challenged by Aeromonas hydrophila were conducted. Also, zooplankton community, diversity, and abundance were evaluated in the cultured water. Five experimental groups (G0, G1, G2, G3, and G4) were exposed to different TAM® concentrations (0, 50, 100, 150, and 200 ml m-3 of culture water, respectively). Healthy 450 mono-sex O. niloticus fingerlings (26.048 ± 0.050 g) were randomly stocked in glass aquariums (150 L aquaria−1, thee replicates treatment−1). The water in aquariums was renewed with a rate of 10% every 4 days and supplied with new freshwater with maintaining the respect TAM® concentrations. The feces and uneaten food were daily removed. The fish were fed at a level of 3% of body weight during the 70-days experimental period. The results revealed that TAM® exposed groups yielded higher significant growth performance, feed intake, and feed utilization compared to the control group. The non-specific immune response (total protein, albumin, globulin levels, and lysozyme activity) and antioxidant enzyme activities were significantly improved with increasing TAM® exposure levels. The resistance of O. niloticus against Aeromonas hydrophila challenge improved significantly in different TAM® treatments. Comparing to the control, TAM® treatments improved the zooplankton community, diversity, and abundance. Due to TAM® photobiotic, applying TAM® levels (especially G4) are significantly flourishing the abundance of Rotifera and Polychaeta, while, inhibiting the abundance of Nematoda, Trematoda, and Insecta. Finally, it can be concluded that the aqueous exposure to seaweed extract TAM® could improve fish growth performance, health status, and resistance against pathogenic bacteria challenge. In addition, it has a desirable modulation effect on natural microbiota in the fish rearing water.