Effects of Pleurotus pulmonarius stalk waste extract-supplemented feed on the immune responses of red hybrid tilapia Oreochromis sp. following challenge with pathogen-associated molecular patterns

Intensive farming of red hybrid tilapia Oreochromis sp. significantly increases the emergence of infectious diseases. Recently, dietary administration of functional feed additives is gaining popularity as an alternative to antibiotics and chemotherapeutics. Mushroom stalk waste (MSW), which possesses the same therapeutic effects as the fruiting body, has immense potential as a cost-effective feed additive in aquaculture. In the present study, 10 g/kg of the ethanol-pretreated hot water extract (E-HWE) of Pleurotus pulmonarius stalk waste was supplemented in the feed of red hybrid tilapia for a 30-day period to determine the effects on growth performance and immune activation after challenging the fish with pathogen-associated molecular patterns (PAMPs). Results showed that E-HWE supplementation significantly improved (p < 0.05) the feed conversion ratio, protein efficiency ratio and hepatosomatic index in red hybrid tilapia but had no apparent effect on the growth. Upon PAMPs challenge, the phagocytic activity and respiratory burst activity of blood leukocytes were significantly enhanced (p < 0.05) in E-HWE-supplemented group. E-HWE supplementation also resulted in significantly higher (p < 0.05) serum haemolytic activity and bactericidal activity. All immune-related genes investigated were upregulated in E-HWE-supplemented group; il1b, tnfa and tlr3 revealed higher expression levels at day 1 post-PAMPs challenge, while ighm and tcrb genes expression levels were elevated after 3 days PAMPs challenge. This study revealed that E-HWE could be a promising and cost-effective feed additive in red hybrid tilapia farming which may also provide a solution for MSW disposal.