Chemical characterisation and in vitro assessment of two mushroom stalks as prebiotics for Clarias gariepinus (Burchell, 1822)

The potentials of mushroom stalks as supplements in aqua-feeds have been grossly underutilised. Stalk meals of two Pleurotus species were analysed for proximate composition, fibre fractions, mineral and phytochemical constituents. In vitro digestibility and fermentability were assessed using caecal digesta from Clarias gariepinus (n = 108; weight: 138 ± 10.8 g). Stalks of Pleurotus pulmonarius and Pleurotus ostreatus were air-dried at ambient room temperature and milled. Pleurotus ostreatus contained higher (P < 0.05) moisture, crude protein, ether extract and crude fibre than P. pulmonarius stalks which had higher (P < 0.05) nitrogen-free extract. Pleurotus ostreatus had higher (P < 0.05) neutral detergent fibre, acid detergent fibre, acid detergent lignin and cellulose but lower (P > 0.05) hemicellulose than P. pulmonarius. Except in manganese and iron content, P. ostreatus contained higher (P < 0.05) sodium, calcium, magnesium, potassium, phosphorus, copper and zinc than P. pulmonarius. Both stalks contained flavonoids, phlobatannin, terpenoid, cardiac glycosides, steroids and antraquinone. Substrate loss was higher (P < 0.05) in P. pulmonarius (0.20 g) than P. ostreatus (0.15 g). Maximum rate of gas production was more (P < 0.05) for P. pulmonarius (0.16 mL/h) at 4.96 hours compared to 0.04 mL/h at 6.04 hours for P. ostreatus. Both stalk meals were partially resistant to in vitro digestibility and were fermentable. Hence, they possess favourable prebiotics characteristics and can be used as supplement in aqua feed.