This study done by Stellenbosch University explores the potential use of hydrolysable tannins in the diets of African catfish (Clarias gariepinus). Hydrolysed tannins extracted from sweet chestnut wood (Castanea sativa) are known for their antioxidant, antimicrobial, and astringent properties, and are effectively incorporated in livestock feeds to reduce the impact of production and environmental stress and to reduce antibiotic use. A commercially available tannin extract (Farmatan Aqua, Tanin Sevnica Slovenia) was included in an extruded catfish grower diet at seven increasing levels (0, 0.5, 1, 1.5, 2, 2.5 and 3 g/kg) and fed for the duration of a 90-day growth trial to establish influence on production performance, meat quality, haematology and intestinal morphology. Each treatment was replicated seven times. After the growth trial, one fish from each treatment was transferred to separate static tanks where water quality parameters were monitored over a 24-hour period at one-hour intervals after one feeding.
Results from this study showed that the inclusion of 1g/kg tannin extract significantly improved feed conversion efficiency from 1.27 (0 g/kg) to 1.22:1 while survival was significantly improved from 79 to 87% at 1.5g/kg inclusion. Haematocrit measurements increased linearly with tannin inclusion (y = 1.5235x + 24.546; R² = 0.9048). Fillet Drip-loss were significantly reduced with 1.5% at 1.5g/kg inclusion and cooking loss with 10 and 15% at 2 and 2.5g/kg inclusion. Ammonia accumulation over a 24-hour period was significantly reduced (y = 4.3401x2 - 25.735x - 5.8066, R² = 0.883) with up to 45% at 3g/kg tannin inclusion
The results from this research offer an opportunity to improve production performance and meat quality while supporting water quality management of catfish production whilst reducing its environmental impact.