EVALUATION OF OCIMUM GRATISSIMUM L. AND EUCALYPTUS GLOBULUS ( LABILL.) LEAVES AS GROWTH PROMOTERS OF THE GIANT AFRICAN CATFISH (HETEROBRANCHUS BIDORSALIS (GEOFFROY SAINT – HILAIRE 1809) FINGERLINGS

Abstract

This study was aimed at investigating the effect of Ocimum gratissimum and Eucalyptus globulus leaves on growth of the Giant African Catfish (Heterobranchus bidorsalis) fingerlings through dietary supplementation. The experiment was carried out in two phases. In the first phase (Experiment I), H. bidorsalis fingerlings were fed with dietary supplementation of O. gratissimum leaf powder at varying inclusion levels of 0.00 (control), 0.5, 1.0, 1.5 and 2.00 g/ 100 g of 40 % crude protein diet for 70 days. The graded levels of O. gratissimum were 0.0g (control), 0.5g, 1.0g, 1.5g and 2.0g per 100g for each diet denoted as CTR, OG1, OG2, OG3 and OG4 respectively in diets 1, 2,3,4 and 5 for H. bidorsalis. In the second phase (Experiment II), H. bidorsalis fingerlings were treated with dietary supplementation of Eucalyptus globulus leaf powder at varying inclusion levels of 0.00 (control), 0.5, 1.0, 1.5 and 2.00 g/ 100g of 40 % crude protein diet for 70 days. The graded levels of E. globulus are 0.0g (control), 0.5g, 1.0g, 1.5g and 2.0g per 100g for each diet denoted as CTR, EG1, EG2, EG3 and EG4 in diets 1, 2,3,4 and 5 for H. bidorsalis. In both phases fish were stocked at a stocking density of 10 fingerlings per 40 cm x 30 cm x 35 cm plastic tanks with each treatment in triplicate. The mean stocking weight of H. bidorsalis in the two experiments was 12.05 ± 0.1 g and 12.24 ± 0.02 g respectively. The fish were acclimated for seven days before the commencement of the experiment. The fingerlings were fed diets containing 40 % crude protein twice daily between 08:00-09:00 h and 18:00-19:00 h GMT. All groups were fed their respective diets at 5% body weight/day. Each group of fish were batch weighed fortnightly to monitor growth and adjust feeding rates accordingly. At the end of the feeding experiments, fish were weighed to estimate growth performance, nutrients utilization and carcass characteristics. Histological examinations of the small intestine, liver and kidney as well as fish blood analyses were carried out following standard procedures. The proximate composition of experimental diets, O. gratissimum and E. globulus leaves and fish carcass as well as fatty acid composition of fish were determined following standard procedures. All data were subjected to one-way ANOVA using Statistical Package for Social Science (SPSS), version 22.0. Significant means were separated using Duncan’s New Multiple Range Test. Results from experiment 1 showed significant differences (P < 0.05) in the growth performance and nutrient utilization indices of H. bidorsalis with the best weight gain and feed conversion ratio were recorded in treatment OG3 (1.5 g /100 g O. gratissimum) while the highest value was recorded in treatment CTR (0.00g/100g O. gratissimum). The 4 th order polynomial regression model showed that a significant and moderately strong relationship existed between the weight gain and O. gratissimum concentration (g/100g) in the fish diets and a differential equation (y = -15.227x 4 + 53.533x 3 - 54.453x 2 + 17.887x + 22.07; R2 = 1) showed that highest weight gain (29.97g) occurred at O. gratissimum level of approximately 1.65 g/100g. Significant differences (p<0.05) occurred in the crude protein and crude lipid contents of the experimental fish which increased with increasing inclusion of O. gratissimum. Improvements occurred in the haematological profile of fish fed varying inclusion levels of O. gratissimum. Significant differences (p<0.05) occured in the total mono-unsaturated fatty-acids (MUFAs), total saturated fatty acids (SFAs) and total poly-unsaturated fatty acids (PUFAs) in the fish fed experimental diets. There were no visible lesions in the enterocytes, mild to no vacuolation of the hepatocytes and no pathological lesions in the kidney parenchyma. Results from experiment 2 showed significant differences (P<0.05) in the growth and nutrient utilization indices of the experimental fish. Fish fed 1.0 g/ 100 g E. globulus powder inclusion level has the highest percentage weight gain and specific growth rate of 173.45±31.79 and 1.41±0.17 respectively. The feed conversion ratio among the treatments were significantly different (p<0.05) from those observed in the control. However, the best feed conversion ratio (FCR) was recorded in fish fed 1.0% E. globulus (EG2). The 4 th order polynomial regression model depicted that a significant and moderately strong relationship existed between the weight gain and E. globulus concentration (g/100g) in the fish diets. A differential equation (y = 13.433x 4 - 46.633x 3 + 38.922x 2 + 0.8983x + 14.56R2 = 1) shows that optimum weight gain occurred at E. globulus level of approximately 0.85 g/100g dietary supplementation. Fish fed E. globulus supplemented diet had a significantly (p ≤ 0.05) higher protein content than the control. There were significant improvements in the haematological profile of fish fed varying inclusion levels of E. globulus. Significant differences (p<0.05) occurred in the mono-unsaturated fatty-acids (MUFAs) and poly- unsaturated fatty acids (PUFAs) of the experimental. There were no visible lesions in the enterocytes of small intestine, fatty infiltration to karyolysis of nucleus occured in the liver and extensive haemosidirine in kidney parenchyma. Thus, O. gratissimum and E. globulus can be used as growth promoters in the diet of H. bidorsalis with a dose of 1.5 g and 1.0 g per 100 g of 40 % crude protein diet respectively.