Dietary effects of artemisia afra on stress response in oreochromis mossambicus and clarias gariepinus

Abstract

The aim of this study was to investigate the anti-stress properties of the A. afra essential oil in Oreochromis mossambicus and Clarias gariepinus subjected to different stressors, namely handling, feed deprivation and stocking density. Ten percent (10%) Artemisia afra was reported to boost immunity in O. mossambicus and C. gariepinus. Artemisia afra contains active ingredients such as polyphenols, phenols, tannins, saponins, flavonoids, carotenoids, alkaloids, and Vitamin C, compounds with various functions such as antioxidant properties. Two diets D1 (0%) and D2 (10%) A. afra were formulated and randomly fed to triplicate groups of Oreochromis mossambicus (30.65 ± 4.61 g) and Clarias gariepinus (38.36 ± 4.89 g) stocked at 15 fish per treatment in a 1000 L tank, filled to a 900 L mark. Fish were fed twice daily (09:00hr and 15:00hr) until apparent satiation. The effect of handling stress on the opercular beat rate, growth performance, and innate immunity in O. mossambicus and C. gariepinus fed with A. afra-based diets was investigated over a period of 45 days. Different fish species respond differently to handling times, therefore, handling times in O. mossambicus were control (0), 10, 15, and 20 minutes. In C. gariepinus, the handling times were control (0), 15, 30, and 45 minutes. All fish were scooped out of the tank and were handled by gripping the whole body twice daily (09:00hr and 15:00hr) for 3 days a week. Control denotes that there was no fish handling. The results indicated that an increase in opercular beat rate was much higher (P < 0.05, ANCOVA) in fish fed with the 0% A. afra-based diet than in fish fed with a 10% A. afra-based diet. This may indicate that fish fed with the 0% A. afra-based diet were more reactive to handling, leading to a higher opercular beat rate, which resulted in stress. Specific growth rate and feed intake in both fish species decreased significantly (P < 0.05, ANCOVA) in fish fed with the 0% A. afra-based diet than in fish fed with the 10% A. afra-based diet. The highest SGR and lowest FCR were observed in tilapia handled for 20 minutes and catfish handled for 45 minutes. Mortality rates also showed that 10% A. afra-based diet possesses compounds that assist with improving growth as there were no mortalities in fish fed with the 10% A. afra-based diet. This shows the positive effect of supplementing 10% A. afra-based diet in the diets of both fish species. The best plasma cortisol and blood performance were observed in fish fed with the 10% A. afra-based diet than in fish fed with the 0% A. afra-based diet; and it was denoted in O. mossambicus handled for 20 minutes and C. gariepinus handled for 45 minutes. Lysozyme activity was not influenced (P > 0.05, ANCOVA) by handling times in both fish species fed with the 10% A. afra-based diet, whereas lysozyme activity in fish fed with the 0% A. afra-based diet significantly declined with increasing handling times (P < 0.05, ANCOVA). This indicates that there was high resistance against handling, thus strengthening the body's ability to fight against stressors and diseases in fish fed with the 10% A. afra-based diet. These results indicated that the opercular beat rate, growth performance, and innate of O. mossambicus and C. gariepinus fed with the 10% A. afra were not affected by handling stress. Therefore, the null hypothesis is accepted. The second experiment was conducted to evaluate the effect of feed deprivation periods on the opercular beat rate, growth performance, and innate immunity in O. mossambicus and C. gariepinus fed with 0% and 10% A. afra inclusion levels over a period of 45 days. Different fish species respond differently to feed deprivation periods, therefore, feed deprivation periods in O. mossambicus were control (0), 3, 6, and 9 days whilst feed deprivation periods in C. gariepinus were control (0), 6, 12 and 18 days. Control denotes that there was no feed deprivation. The opercular beat rate in feed deprivation followed the same trend as handling stress (P < 0.05, ANCOVA). Fish fed with the 10% A. afra-based diet recorded the best growth performance (SGR, FCR and feed intake) than fish fed with the 0% A. afra-based diet. The best growth performance was observed in O. mossambicus and C. gariepinus deprived of feed for 6 days and 12 days, respectively. This may indicate that 10% A. afra-based diet helped in maintaining gut health during the 6 days and 12 days of feed deprivation period in both species, which allowed better digestion and higher feed intake when the food was reintroduced. The results on mortality rates were similar to handling stress. Plasma cortisol was not influenced (P > 0.05, ANCOVA) by feed deprivation periods in both fish species fed with the 10% A. afra-based diet. This may explain why plasma cortisol levels did not rise when fish were under feed deprivation stress. The best glucose levels and blood performance were observed in O. mossambicus deprived of feed for 6 days and C. gariepinus deprived of feed for 12 days fed with the 10% A. afra-based diet. Lysozyme activity followed the same trend as handling stress. The results of this experiment demonstrated that the opercular beat rate, growth performance, and innate of O. mossambicus and C. gariepinus fed with the 10% A. afra were not affected by feed deprivation periods. Additionally, it shows that the 10% A. afra-based diet improved better feed intake, thus affecting growth. Therefore, the null hypothesis is accepted. The last experiment evaluated the effect of stocking density on the opercular beat rate, growth performance, and innate immunity in O. mossambicus and C. gariepinus fed with 0% and 10% A. afra-based diets over a duration of 21 days. The stocking density experiment was limited to 21 days. This shorter duration was sufficient to observe the acute effects of elevated stocking density, such as immediate stress responses, increased competition for resources, and rapid changes in growth performance or opercular beat rate. The fish were stocked in 500 L fibreglass tanks in a completely randomized design. The fish stocking densities for both fish species were as follows; low stocking density (LSD): 1.44 kg/m3 (45 fish/treatment), medium stocking density (MSD): 2.63 kg/m3 (75 fish/treatment), and high stocking density (HSD): 3.68 kg/m3 (105 fish/treatment). The experimental system used for both fish species was the same. In O. mossambicus fed with the 10% A. afra-based diet, the best (P < 0.05, ANCOVA) SGR, feed intake, FCR, and lowest opercular beat rate were recorded at high stocking density (3.68 kg/m3). This suggest that 10% A. afra-based diet maximized feed intake and SGR while minimizing the effects of stress and fish were able to convert feed into body mass efficiently, leading to optimal growth at high stocking density. The highest SGR, feed intake, best FCR and lowest opercular beat rate in C. gariepinus fed with the 10% A. afra-based diet were recorded at medium stocking density (2.63 kg/m3) (P < 0.05, ANCOVA). At medium stocking densities, there was no competition for food and space and as a result, fish stress did not occur. The fish may have been able to channel their energy to feeding instead of fighting stress. Mortality rates were similar to that observed in handling stress and feed deprivation experiments In O. mossambicus, fish fed with the 10% A. afra-based diet recorded the best (P < 0.05, ANCOVA) plasma cortisol, glucose levels compared and blood performance than fish fed with the 0% A. afra-based diet. The lowest plasma cortisol, glucose and blood performance in C. gariepinus was recorded in fish fed with the 10% A. afra-based diet than in fish fed with the 0% A. afra-based diet at medium stocking density (2.63 kg/m3). This may indicate that the 10% A. afra-based diet inclusion may have helped in stabilizing osmotic balance and reducing physiological stress, leading to lower cortisol and glucose levels. These results indicated that the opercular beat rate, growth performance, and innate of O. mossambicus and C. gariepinus fed with the 10% A. afra were not affected by stocking density. Hence, the null hypothesis is accepted. The study showed that Artemisia afra essential oil have the potential to reduce stress when supplemented in the diets of two commonly warm freshwater species when subjected to handling stress, feed deprivation and stocking density. Reducing the stocking density is recommended to maximize the growth and innate immunity of catfish at high densities. While high stocking densities are often necessary in catfish culture to reduce cannibalism, particularly during early developmental stages; excessively high densities can lead to negative impacts on growth performance, water quality, and immune function. Therefore, stocking density must be carefully optimized to balance the reduction of cannibalism with the maintenance of physiological health and growth. Moderately high densities may provide a compromise by minimizing cannibalism without excessively compromising innate immunity and growth. At farm levels, fish can be handled and deprived of feed without adversely affecting the growth and health of fish when supplemented with A. afra essential oil at a concentration of 10%. This may increase warm freshwater aquaculture production and improve the livelihood of local fish farmers.