Anathi Mbona - Academia.edu (original) (raw)

Papers by Anathi Mbona

In the aquaculture of fish and shrimps, diets generally contain high levels of fish meal. Fish me... more In the aquaculture of fish and shrimps, diets generally contain high levels of fish meal. Fish meal is a nutrient rich feed that contains essential amino acids and fatty acids, which are required to maintain optimum growth and health of an animal. It is traditionally used in aquaculture to promote feed efficiency, nutrient uptake and feed intake due to its high palatability and digestibility. Overexploitation of fisheries resources and the high growth rate of aquaculture industry, however, continues to put pressure on the supply of fish meal, thus increasing the demand and price of this sought-after product. The use of alternative ingredients to fish meal, therefore, remains a high priority for aquaculture nutrition. Hence, the aim of this was to investigate the physiological and developmental effects on juvenile spotted grunter, Pomadasys commersonnii, after supplementing fish meal with different feed additives for 12 weeks. One of the additives was then selected for further feeding at graded levels (increasing levels) for 8 weeks to ascertain whether fish meal could be replaced by higher amounts of the feed additive without negative consequences to the cultured spotted grunter. P. commersonnii is a marine fish that inhabits the warm waters of the Indian Ocean along the east coast of South Africa. The species is suitable for human consumption and has been identified as a potential finfish for marine aquaculture. Growth rate, feed efficiency and health parameters were investigated after feeding 6 experimental diets to spotted grunter for 12 weeks; the data was compared to those fish that were fed on a non-supplemented control diet of fish meal. The experimental diets were based on fish meal, but supplemented with one of the following additives: algae (Spirulina platensis and Ulva lactuca), yeasts (Candida utilis and Saccharomyces cerevisiae), and commercial herbal additives (LIV-UP ® and UNP PB-20 ®). Growth performance indicators were measured using the body weight, length and specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) that is, the ratio of weight gain to the amount of protein consumed over time. The assimilation of nutrients from the feed was assessed by a proximate composition v analysis in fish body, evaluating hepatosomatic index (HSI) and visceral fat index (VFI), as well as measuring glycogen content in the liver. The health status of the fish was evaluated from histological analyses of the distal intestines, blood glucose concentration and by determining the condition factor (K). The condition factor is the relationship between length and fish body weight and was used to evaluate the health condition of fish under changing environmental factors. After the feeding period of 12 weeks, supplemented diets significantly increased the body weight, length, condition factor and FCR of spotted grunter when compared to the control diet. The growth performance of fish fed on C. utilis surpassed all the other treatments. However, fish fed on Spirulina supplemented diet had the best FCR when compared to the control. Moreover, there was a significant increase in specific growth rate (SGR), despite individual variation, in fish fed with C. utilis (2.14 ± 0.21 %/day). In contrast, the calculated SGR for the control group was 0.95 ± 0.09%/day. Similarly, the condition factor increased from 2.62 ± 0.27 for fish fed the control diet to 3.28 ± 0.34 for fish fed the C. utilis containing diet at the end of the feeding trial. Furthermore, the hepatosomatic index (HSI) was significantly affected after 12 weeks of feeding different diets. The HSI decreased from 1.42 ± 0.19 to 1.07 ± 0.10% for fish fed on U. lactuca and UNP PB-20 ® containing diets, respectively. No significant difference was observed in visceral fat index (VFI) after the feeding period of 12 weeks. The addition of different feed additives in fish diets increased the deposition of visceral fat compared to the control. Similarly, blood glucose and liver glycogen content was affected by the addition of different ingredients in fish diets. Fish fed C. utilis included diets mediated the highest blood glucose content (5.59 ± 0.55 mmol/L) when compared with the control group value after 12 weeks of feeding. A significant difference was observed in liver glycogen levels of fish fed the respective diets. The glycogen content of the fish liver significantly decreased from 126.41 ± 6.87 to 65.94 ± 2.94 mg/g for fish fed on C. utilis and UNP PB-20 ® supplemented diet. The addition of C. utilis, U. lactuca and UNP PB-20 ® in spotted grunter diets increased the frequency of goblet cells in the distal intestine after 12 weeks of feeding. The S. platensis and S. cerevisiae fed fish mediated the longest mucosal folds, while S. platensis and C. utilis fed groups vi distinguished themselves with complex mucosal folds. These results suggest that the growth performance and feed utilization of spotted grunter can be enhanced by the addition of feed additives. The slow growth rate of fish fed on diets containing U. lactuca and LIV-UP ® corresponds with an observed increase in HSI, VFI and well-established signs of intestinal enteritis. The observed increase suggests that spotted grunter was unable to fully utilise the supplemented feed additives, which might explain the reduced growth rate. The replacement of fish meal with increasing levels of the best performing diet (torula yeast) was evaluated in a second investigation to determine the effects of yeast on growth, feed utilization and health of spotted grunter. Experimental diets with increasing percentages of C. utilis (i.e. 0, 4, 8, 12, 16 and 20%) were fed to spotted grunter for 56 days. No significant differences (p > 0.05), were observed in all treatments for body weight gain, fish length, SGR and condition factor. There was trend of increase in the VFI of fish fed increasing levels of yeast, ranging from 3.44 ± 1.28 to 5.27 ± 0.92%, although the values were statistically non-significant. The HSI and blood glucose of fish were not affected by increasing percentage of yeast after 56 days of feeding. However, the glycogen storage in the fish liver was significantly affected by increasing levels of yeast after 56 days of feeding. The glycogen storage tended to decrease as the amount of C. utilis in the diet was increased, decreasing from 74.19 ± 5.37 to 54.54 ± 1.01 mg/g for fish fed on 8 and 20% yeast containing diet, respectively. The addition of 20% yeast in fish diets resulted in reduced height of intestinal folds, thickening of the submucosa and lamina propria, increased frequency of goblet cells and diminishing absorptive vacuoles while insignificant signs of enteritis were observed in other diets after 56 days of feeding graded levels of yeast. The results suggest that an optimum dietary concentration of 16% C. utilis in spotted grunter diets facilitates better growth rate and feed efficiency without any negative health effects. In conclusion, the results of this study showed that C. utilis can be added in formulated diets for spotted grunter to enhance rapid growth rate and an optimum concentration of 16% C. utilis can be added in fish diets to improve growth and feed efficiency with no adverse health effects in fish. vii