Red Earthworm (EW), Perionyx excavates , could be an excellent source of aquafeed as it contains a high amount of nutrients and has the potential to be an alternative protein source for fishmeal (FM). The purpose of this study was to examine the impact of substituting FM protein with EW meal on the growth, haemato-biochemical response, intestinal histomorphology, and lipid droplets assessment in the liver and muscle tissue of Nile tilapia, Oreochromis niloticus .
For the study, four different diets were tested, including an FM-based reference diet (control) and three test diets with the EW meal replacing FM in proportions of 10% (D1), 20% (D2), and 40% (D3). Nile tilapia, with an initial weight of 3.47±0.02g, were fed the experimental diets for 56 days.
The results indicated that replacing up to 20% of fishmeal with EW meal (D1 and D2) did not have any adverse effects on weight gain and the specific growth rate of fish. Quadratic analysis between FBW and EW meal showed the best growth performance when replacing 17.5% FM with EW in the diet. However, adverse effects were observed at the 40% replacement level (D3) compared to the control. The feed conversion ratio and survival rate appeared to be similar in all dietary groups. Condition factor was significantly reduced (p<0.05) compared to the control diet when replacing the highest (40%) FM by EW meal in the diet.
Fish fed the D3 diet had a significantly decreased height and width of intestinal mucosal folds and the number of mucosal goblet cells compared to the control (p<0.05). Although red and white blood cell counts (RBC and WBC, respectively) were found unchanged between the control, the D1 and the D2 dietary groups, a significantly higher number of WBC and a lower number of RBC were found in the D3 group when compared to the control. Blood glucose level was higher in the D3 group, while the haemoglobin level was the lowest in the same group. A significantly (p<0.05) higher frequency of erythrocyte cellular and nuclear abnormalities were noted in fish fed the D3 diet.
Furthermore, lipid droplet accumulation in the liver and muscle was significantly higher in D3, whereas diet D1 and D2 showed no significant difference compared to the control. Overall, the study indicates that up to 20% EW could replace fishmeal in the diet of Nile tilapia without compromising growth and the examined key physiological parameters.