Doctoral Degrees (Animal Sciences)

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Browsing Doctoral Degrees (Animal Sciences) by Subject "African catfish (Clarias gariepinus) -- Breeding"

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    Application of dietary bentonite clay as feed addictive on feed quality, water quality and production performance of African catfish (Clarias gariepinus)
    (Stellenbosch : Stellenbosch University, 2016-03) Ayoola, Mathew Oluwaseyi; Salie, Khalid; De Wet, Lourens; Stellenbosch University. Faculty of Agrisciences. Dept of Animal Sciences.
    ENGLISH ABSTRACT: Aquaculture remains the fastest growing animal food producing sector and is gradually overtaking capture fisheries as a source of food fish. The challenges of poor feed quality, feed utilisation and water quality are recurring issues that hinder the growth of aquaculture industry. This study investigated the effects of natural bentonite (NB) and its acid activated form (AB) as feed additives on aquafeeds with reference to the physical quality, growth performance, gut evacuation rate and water quality with African catfish (Clarias gariepinus) as the experimental species. Bentonite clay has found application as a feed additive in animal science and aquaculture. It is used as a mycotoxin binder to improve feed utilisation. Application of dietary activated bentonite form is yet to be fully elucidated to the best of our knowledge. Aquafeeds’ physical qualities, including water stability, feed durability, feed bulk density and nutrient leaching, were investigated. Dietary bentonite clay was added to commercial aquafeeds and each treatment were replicated four times. Water stability, feed durability, feed bulk density and nutrient leaching were all significantly affected (p<0.05) by treatments. Measured parameters (water stability, feed density and feed durability) increased (p<0.05) with the quantity of AB in the clay blend and at high inclusion level as compared to control. Values increased with an increased inclusion level of clay in feed, while nutrient leaching value decreased with quantity of AB and high inclusion. AB had higher values as compared to NB and the control. These results validated the potential utilisation of NB and AB as feed binders. Their ability to improve pellet physical qualities is expected to enhance feed utilisation, maintain good water quality and increase fish growth. Aquafeeds with bentonite clay blend, and each at different inclusion levels improved (p<0.05) growth performance, feed conversion ratio (FCR), specific growth rate (SGR), red blood cell (RBC), and haematocrits (HCT). Parameters improved with an increase in quantity of natural bentonite and at low inclusion level. Growth performance increased (p<0.05) as compared to control with bentonite inclusion up to 1500 mg/kg and decline at 3000 mg/kg. The contents of crude protein (CP), fat, moisture, ash and abdominal fat in the whole body composition were significantly affected (p<0.05) by the treatment diets. Abdominal fat and tissue fat content increased with bentonite inclusion. To evaluate the effect of NB and AB on gut evacuation rate of Clarias gariepinus, fish were randomly allocated to treatment diets and fed ad libitum. Four (4) fish were randomly selected per treatment to measure post feeding stomach content (SC) and intestinal filling (IC) content at (5, 30, 60 and 120 min). The control diet had higher values for SC at 5 min which differed significantly (p<0.05) as compared to clay diets. SC decreased (p<0.05) with time in all diets and clay diets had higher value (p<0.05) between (30 – 120 min) as compared to control. In clay diets, SC decreased faster over time with reduced quantity of AB and low inclusion level. The IC of control diets had higher values (p<0.05) over time as compared to clay diets. The water quality parameters (pH, N02-, NH3-N and TSS) were evaluated in a static aerated tank. Aquafeeds were fed to adult fish at 3% body ratio twice daily. Each treatment diet was replicated four (4) times, and 10 fish were randomly allotted to each tank. The water temperature was 25 ± 2°C and dissolved oxygen (DO) was 3-9 mg/L. Water samples were collected daily from each tank. In phase I, water quality was evaluated over seven (7) days, and in phase II over five (5) days. No mortality was recorded during the study. The values of pH, N02-, NH3-N and TSS increased significantly (p<0.05) in all treatment diets over time. In both phases, clay treated diets had lower values for measured parameters (p<0.05) compared to those of control. In clay diets, values increased (p<0.05) with quantity of AB and high inclusion level. Fish feed intake reduced as water quality deteriorated, and uneaten feeds contributed to increase in poor water quality. Thus, high water stability of clay treated diets attributed to maintenance of good water quality as compared to the control. The results showed that dietary clay enhanced feed binding, which affected digesta viscosity. This reduced the rate of feed evacuation in the gut, and, thus, enhanced proper breakdown and absorption of nutrients. Higher inclusion levels of bentonite clay and increased quantity of AB are not suitable for improved growth and feed utilisation, as increased in digesta viscosity led to fermentation in the gut. An optimum level of performance was recorded at 1500 mg/kg inclusion with natural bentonite (B1500) with a significantly (p<0.05) better performance as compared to control and acid activated bentonite. A clay combination blend up to 50% (A50B50) at low inclusion level (500 mg/kg) of acid activated bentonite is considered optimum.