Browsing by Author "Groenewald, Niklaas Jakobus"

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    Comparison of growth performance of Nile tilapia (Oreochromis niloticus) fingerlings fed different inclusion levels of black soldier fly (Hermetia illucens) pre-pupae meal diets and its effect on the physical characteristics of the feed
    (Stellenbosch : Stellenbosch University, 2018-03) Groenewald, Niklaas Jakobus; Pieterse, Elsje; Salie, Khalid; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: The nutritional composition of fish and the health benefit associated with the consumption thereof makes it a valuable food and feed source for both humans and animals. However, with the increasing size of the world’s population and the demand for fish and other fishery products, an increased amount of pressure is being placed on wild catch fisheries. As a result, the latter are becoming stagnant, or declining, in many regions around the world. Aquaculture has, to some extent, been able to relieve the pressure placed on wild catch fisheries. Yet, a major downfall is that it still relies on wild caught fish to be used as a protein source for many aquaculture fish species. Various alternative protein sources has been investigated for use in aquaculture feeds to replace conventional and unsustainable protein sources, such as fishmeal. Among the various alternative animal protein sources, the use of insects are gaining popularity as a promising and sustainable solution. Insects are a natural food source for many fish species and have relatively balanced amino- and fatty acid profiles, while it is also highly effective in integrated waste management (IWM) systems. The objective of the study was to investigate the effects of different inclusion levels of black soldier fly (BSF) (Hermetia illucens) pre-pupae meal in the diets of Nile tilapia (Oreochromis niloticus) fingerlings (n = 630) on the growth performance, fillet yield and feed quality. Six diets were compared: BSF0 (0 %; the control diet), BSF5 (5 %), BSF10 (10 %), BSF15.6 (15.6 %), BSF20 (20 %) and BSF25 (25 %; the summit diet). There were no significant differences in the final average body weight, feed intake, average daily gain (ADG) and conditioning factor (CF) between the different treatments. There was no significant difference for the feed conversion ratio (FCR) of BSF0 (1.35) and BSF5 (1.50), however FCR was lower (P≤0.05) for BSF10 (1.63) relative to BSF0, and worsened with increasing inclusion levels. The FCR was not significantly different between BSF10 and BSF15.6 (1.79), but BSF10 did have a significantly lower FCR than BSF20 (1.97) and BSF25 (1.91), whilst the latter two did not differ (P>0.05) from each other. During the preparation of the experimental feed, the inclusion of a binder was required in BSF20 and BSF25 in order to prevent complete crumbling with the extrusion process. The use of a binder changed the hardness and floating characteristics of diets BSF20 and BSF25, which may have had an influence on differences in FCR. There was no significant difference observed for specific growth rate (SGR) between BSF0 (2.05), BSF5 (1.91) and BSF10 (1.73), or between diets BSF10 through to BSF25 (1.62). Treatment BSF10 was thus not significantly different from any treatment diets. Treatment BSF0 was the only diet with a SGR significantly higher than BSF15 (1.68), BSF20 (1.60) and BSF25 (1.62). The protein efficiency ratio (PER) of BSF0 (2.02) and BSF5 (1.82) did not differ significantly from each other. The PER of BSF0 differed significantly from BSF10 (1.68), BSF15.6 (1.55), BSF20 (1.40) and BSF25 (1.43). The difference could be linked to the increasing lipid content of the feeds which is known to adverse effect the digestibility of the feeds. The carcass yield was not significantly different between any of the treatments, where all the yields (percentage body weight) ranged from 81.63 g (BSF20) to 83.5 g (BSF0). The fillet yield did show some variation, but the results are not very accurate (R2=0.094) due to the methodology of filleting. Furthermore, no significant differences were observed for the proximate composition (moisture, crude protein, lipid and ash) of the fillets. The inclusion level of the BSF pre-pupae meal showed a statistically significant influence on the unit density, sinking velocity, water uptake and leaching rate of the pellets. However, the effect of binder used in BSF20 and BSF25 may have had an influence on these results. All unit densities differed significantly from each other, increasing with higher BSF pre-pupae inclusion levels. The control (BSF0) and BSF5 had a sinking velocity of 0 (floating pellets), while the feed only started sinking with inclusion levels of 10 % BSF pre-pupae meal (BSF10, 4.44 cm/s). Faster sinking velocities were observed with increasing inclusion levels of BSF pre-pupae meal. Water uptake was generally higher in BSF0 compared to other treatments for all the timeframes, except for the shortest submersion time (5 min), where BSF15.6 (288.60 %) had a significantly higher water uptake than all the other diets. Due to the disintegration of the pellets over time, the water uptake was expressed as a percentage of feed remaining rather than initial quantity used. The feed remaining was used to determine disintegration rate. Factors such as lipid content and interactions between ingredients may have indirectly influenced feed quality parameters. The study did not generate enough evidence to verify the claim that BSF pre-pupae meal can be used as a viable alternative protein source to conventional sources in Nile tilapia feeds, due to variability in water stability and inclusion of a binder that were not accounted for. However, it was found that inclusion levels of up to 25 % can be used without any effect on the body composition, and up to 5 % without compromising the growth parameters. Therefore, it is recommended to use an inclusion level of 5 % BSF pre-pupae meal to maintain the growth performance. For future studies, it is suggested to use defatted BSF pre-pupae meal for potentially higher inclusion levels of the meal for comparative growth results relative to conventional protein sources – as the higher lipid content may adversely affect the binding ability and the feed quality.