Masters Degrees (Animal Sciences)

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Browsing Masters Degrees (Animal Sciences) by Subject "Abalones -- Feeding and feeds -- South Africa"

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    Hydrolysed insect proteins as fish meal alternatives in the diets of South African abalone (Haliotis midae)
    (Stellenbosch : Stellenbosch University, 2023-12) Van Schalkwyk, Mighael; Van Zyl, Johan Hendrik Combrink; De Wet. L. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: This research forms part of the global effort towards reduced reliance on fish meal (FM) in aquafeeds. The utilisation of hydrolysed insect protein (HIP) was therefore evaluated against the performance obtained from fish meal-based aquafeed fed to South African abalone. The research presented in this thesis was conducted in three phases and is subsequently presented as such. Phase A evaluated chitin-target hydrolysis through dietary chitinase inclusion within extruded abalone feeds. Chitinase inclusion resulted in significant (P < 0.05) deterioration in water stability (WS). The lowest chitinase inclusion of 0.1% differed significantly (P < 0.05) from the control following 60 min water exposure. A significant reduction in the drying times of the respective treatments was observed. Drying times were correlated with WS and a rapid protocol for WS determination using drying times and drying curves was proposed. However, drying curves did not appear to correlate with WS, but was ascribed to prior drying and prolonged storage of the feeds. Due to the resulting feed disintegration and compromised WS, dietary chitinase inclusion in abalone feeds was not viable. Phase B subsequently evaluated the WS of aquafeeds containing pre-treated hydrolysed insect proteins (HIP), produced via hydrolysis by endogenous (autolysis), or chitinase or amylase enzymes. The respective HIPs were used to replace 20, 40, 60, 80 and 100% of the FM component. A significant (P < 0.05) deterioration in the WS of the amylase and chitinase treatments compared to the control was observed following 360 min WS. Hydrolysed insect protein inclusion resulted in a significant, linear reduction in WS, with 80 and 100% FM replacement (11% and 14% inclusion respectively) yielding significantly (P < 0.05) lower WS compared to the FM control. Moreover, the high HIP amylase treatment consistently yielded lower WS compared to that of the control and chitinase treatments. Despite the significant reduction, the WS of the feeds was determined suitable for a growth-trial. Phase C consisted of a commercial trial to evaluate the growth performance obtained from the respective diets. Eight baskets, stocked with 50 abalone (90 ± 10 g). Moreover, three individual abalone from each basket were tagged with a marked research tag to allow for individual weight and length measurements. No significant differences were observed for any of the measured production parameters between the respective enzymes. Similarly, HIP inclusion had no significant effect on the measured growth parameters. However, the final individual weight of the control treatment was significantly (P < 0.05) lower compared to all other treatments, but similar to the 100% HIP treatment. Dry matter feed intake significantly (P < 0.05) increased with increased HIP inclusions, however, FCR remained largely unaffected, with only the HIP60 treatment significantly (P < 0.05) higher compared to the control. Processing parameters were significantly influenced by the respective enzymes, with the dressing % of amylase treatment yielding the highest visceral weight and percentage. Enzymatic hydrolysis significantly (P < 0.05) increased the brining loss, although canning and cooking resulted in no significant differences in marketable yield. Marketable yield remained unaffected by HIP inclusion, despite a significant reduction in meat mass index with increased HIP inclusions. This study concludes that hydrolysed insect protein is a viable alternative for FM within the diets of South African abalone. The results can contribute towards reduced dependency on FM produced from wild-caught fishers and increase the sustainability of the local abalone industry.