Apparent nutrient digestibility and performance of Heterobranchus longifilis fed with Libyodrilus violaceus meal supplemented-diets
Apparent digestibility coefficients (ADCs) of nutrients is a useful tool for fish diet formulation, which gives the right estimation of growth, thereby reducing waste products. The ADCs of crude protein, energy and dry matter of processed earthworm, Libyodrilus violaceus meal by Heterobranchus longifilis fingerlings (1.06±0.01g) was evaluated at 0 to 100 %. Eleven dry isonitrogenous (40% crude protein) diets were formulated at levels of 0% (control) to 100%. All experimental diets contained chromic oxide at 0.5% as an indigestible marker. The feeding experiment was carried out in 40 L plastic tanks in triplicate treatments using randomized block design. Fingerlings were fed 5% of their body weight twice daily for 12 weeks and faecal samples were collected seven hours after the first feeding of the day. The digestibility coefficients of nutrients was calculated using proximate analyses of feeds and faeces carried out for crude protein, energy and dry matter. Apparent digestibility of protein and energy were highest, 82.0±0.20% and 81.50±0.32% respectively, in fish fed with 60% L. violaceus meal diet and lowest, 78.40±0.40% and 76.20±0.62%, in those fed with the control diet respectively. These values were significantly (p ≤ 0.05) different between the treatments. Apparent digestibility coefficient of dry matter was lowest (82.28±0.09%) in fish fed with the control diet and highest (86.21±2.0%) in those fed 100% diet, and differed significantly (p ≤ 0.05) from other treatments. These findings suggests that replacement of fishmeal with L. violaceus meal at 60% inclusion level in the diet of H. longifilis fingerlings was most suitable for optimum growth, nutrient utilization and protein digestibility.
Keywords: Heterobranchus longifilis; Libyodrilus violaceus; digestibility; growth