GROWTH AND NUTRIENT UTILIZATION OF EARTHWORM MEALS IN THE DIETS OF MUD CATFISH FINGERLINGS  

Abstract

A study was carried out to evaluate the growth, nutrient utilization and digestibility of two tropical earthworms, Alma millsoni and Lumbricus terrestris in the diets of fingerlings of the African mud catfish, Clarias gariepinus and its hybrid (♂Heterobranchus longifilis X ♀Clarias gariepinus), Heteroclarias. Dry meals of the earthworms were used to substitute fishmeal in eleven isonitrogenous (40% crude protein) and isocaloric (480kcal/g) diets at 0% (control), 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% inclusion levels using Pearson Square Method. The experiment was carried out in a completely randomized design in triplicate treatments. Chromic oxide used as the inert marker for digestibility was incorporated into the diets at 0.5%. Fingerlings were fed twice daily and faecal samples were collected seven hours after the first feeding. Apparent digestibility coefficient was calculated for crude protein, energy and dry matter using proximate analysis of diets and faeces. Data were analyzed using descriptive statistics and ANOVA. Highest mean weight gain (18.91±0.01g/fish), relative (1734.86±0.01%) and specific (1.40±0.02%) growth rates were recorded in C. gariepinus fed 70% A. millsoni meal (AMM) diet. Food conversion ratio (3.32±0.01) was lower and significantly (p˂0.05) different in fish fed 70% AMM diet than for all the other diets except 60% AMM diet. Protein efficiency ratio (4.22±0.01) and protein productive values (4.48±0.02%) were higher in fingerlings fed 70% AMM diet and significantly (p˂0.05) different. The apparent digestibility coefficients of protein (90.0±0.28%) and energy (88.34±0.20%) were higher and significantly (p˂0.05) different in fingerlings fed 70% AMM diet than for all the other diets except 60% AMM diet. Heteroclarias fed 50% L. terrestris meal (LTM) diet had the highest mean weight gain (17.50±0.05g/fish), relative (1166.7±4.80%) and specific (1.31±0.01%) growth rates. Food conversion ratio (3.51±0.02) was lowest in fish fed 50% LTM diet, the value was significantly (p˂0.05) different for all the other diets except 40% LTM diet. Protein efficiency ratio (6.25±0.05) and protein productive values (221.42±0.05%) were higher and significantly (p˂0.05) different in fingerlings fed 50% LTM diet than for all the other diets. Apparent digestibility coefficients of protein (90.0±0.50%) and energy (84.0±3.20%) were higher in fingerlings fed 50% LTM diet than all the other diets and the differences were significant (p˂0.05). These results indicate that A. millsoni and L. terrestris can be used to replace fishmeal at 70% and 50% inclusion levels respectively in the diets of C. gariepinus and Heteroclarias fingerlings for optimum growth rate, nutrient utilization and digestibility of feeds.

Keywords: Alma millsoni, Lumbricus terrestris, mudcatfishes, digestibility, growth rate.