In order to investigate the interactions of dietary protein and energy and their utilisation by African catfish, Clarias gariepinus (Burchell, 1822) (12.43 ± 0.05 g), a series of four nutritional experiments (triplicate groups of 20 fish per 30-L tank at 28 ± 1°C, for 8 weeks) were carried out using fish meal based diets. Optimum dietary protein to energy ratio (P/E ratio) and optimum lipid to carbohydrate ratio (L/CHO ratio) were investigated. Based on optimised dietary P/E ratio and L/CHO ratio, optimum feeding regime and compensatory growth were also investigated in this species. In the experiments to optimise P/E ratio and L/CHO ratio fish were offered each diet at 5% of their body weight per day adjusted fortnightly. In the optimum feeding regime experiments, fish were offered each diet to appetite or to a restricted level. The restricted regimes were achieved by offering fish decreasing fixed feeding rates with increasing dietary protein level. Studies on compensatory growth were conducted in two phases each of 4 weeks. In the first phase, triplicate groups of 30 fish and in the second phase triplicate groups of 20 fish (per 30-L tank) were offered the diet in six mixed feeding schedules at two feeding regimes i.e. appetite and restricted. The restricted regime was achieved by offering fish 1% (maintenance ration) of their body weight per day adjusted after fortnightly weighing. Optimum dietary P/E and L/CHO ratios were 20.54-mg protein/kJ of GE and 0.40 g/g respectively, with a crude protein level over 40% and gross energy of more than 20 kJ/g GE. The results of investigating feeding regimes suggest that dietary protein level could be reduced from over 40% to 35% by feeding to appetite based on the above optimised dietary P/E and L/CHO ratios. Addition of dietary energy as lipid at varying protein levels resulted in increased growth, protein and energy utilisation in C. gariepinus. Based on optimised dietary P/E ratio, dietary carbohydrate levels were increased (with concomitant reduction in dietary lipid levels) resulting in a trend towards higher growth performance, protein and energy utilisation. Protein and energy utilisation did not vary (P > 0.05) with feeding regime or dietary protein level. C. gariepinus showed partial compensatory growth under alternating periods of feeding a restricted (maintenance requirements) and appetite ration and also showed higher feed, protein, lipid and energy utilisation efficiencies in comparison to appetite feeding.Increase in dietary lipid produced an increment in carcass lipid deposition, both in whole body and liver in all studies. Fish in all treatments did not show significant differences (P < 0.05) in body protein content. Optimum P/E ratio studies, with varying dietary protein and energy level, produced higher liver glycogen, plasma glucose and plasma triglycerides at higher dietary carbohydrate level with lower protein diets. In the studies to optimise lipid to CHO ratio comparatively lower (P < 0.05) plasma glucose and plasma cholesterol deposition were observed while no consistent trends were found in liver glycogen deposition in fish fed higher dietary lipid with concomitant lower CHO levels. Studies on optimising feeding regime, with varying protein levels, did not show any significant differences (P < 0.05) in liver glycogen, plasma glucose, plasma triglycerides and plasma cholesterol in response to dietary treatment. In all studies fish fed the experimental diets showed insignificant differences (P > 0.05) in plasma amino acid levels and digestive enzyme activities (protease and lipase) while intestinal a-amylase activity increased with increasing dietary carbohydrate level. Histological examination of intestine & liver in all studies showed no abnormalities. In conclusion, these studies suggest that manipulation and optimisation of dietary protein and energy intakes plays a very significant role in African catfish, Clarias gariepinus nutrition.

In my diploma thesis I was tested six types of feed. I tested in 3 repetitions in the recirculating system with biological treatment of water. Tested fishes african catfish (Clarias gariepinus) weighted between 200 ? 800 g per piece, were deployed into 18 aquariums with volume of 190 litres per aquarium. The whole experiment took place in five partial 3-week periods in the intensive breeding of the laboratory - controlled reproduction of fishes FROV JCU. The average water temperature during the experiment was 27 °C. The main objective of the thesis was to observe production efficiency of tested types of feed, speed of the growth of fishes, feed rates and financial costs. Afterwards, determinativ of yield and organoleptic evaluation was determined, followed by laboratory examination of composition of meat. The results of production indicators (Specific Growth Rate, Relative Growth Rate, Food Conversation Ratio) were most favorable for 3 types of feed ? Haltáp (SGR=0,81 %; RGR=126 %; FCR=1,45), Coppens TROCO SUPREME-22 (SGR=0,73 %; RGR=105 %; FCR=1,19), Coppens TROCO PRIME-18 (SGR=0,68 %; RGR=97 %; FCR=1,26). The lowest costs for 1 kg of fish increment were achieved for these specific types of feed Haltáp and Aller Aqua Focus (45 Kč a 46 Kč). In the organoleptic analysis was found positive evaluation of meat of all tested fishes. Chemical composition of meat was (in term of proteins and fats content) most favorably documented for the hungarian feed called Haltáp (proteins=19,22 % and fats=4,85 %).

Durch die Nutzung des fischfutterbedingten Nährstoffeintrags für die kombinierte Produktion von Fischen und Pflanzen können Aquaponiksysteme eine nachhaltige Erweiterung von Kreislaufanlagen der Aquakultur (RAS) darstellen. Herkömmliche Aquakulturfutter zielen jedoch auf Fischproduktion mit geringer Umweltbelastung ab und sind somit nicht für die Aquaponik optimiert. Daher weist RAS-Wasser häufig Mängel im Profil gelöster anorganischer Pflanzennährstoffe auf. So war es Ziel dieser Arbeit, die Auswirkungen unterschiedlicher Proteinquellen auf die Nährstoffdynamik in RAS durch Fütterungsversuche mit Afrikanischem Raubwels und Nil-Tilapia zu untersuchen, bei denen Wachstum, gelöste anorganische Nährstoffkonzentrationen im RAS-Wasser und die Ausscheidung von Nährstoffen über den Kot verfolgt wurden. Der Fokus lag auf nachhaltigen alternativen Proteinquellen zu marinem Fischmehl und terrestrischen Pflanzenproteinen: Larvenmehl der Schwarzen Soldatenfliege (BSFM), Welsschlachtabfallmehl (CM), Geflügelschlachtabfallmehl (PM) und Geflügelblutmehl (PBM). Experimentalfutter, die phosphorreiches PM und CM enthielten, förderten erhöhte Ausscheidung von löslichem reaktivem Phosphor, erzeugten die besten gelösten N:P-Verhältnisse im RAS-Wasser verglichen mit einer Hydroponik-Nährlösung und ermöglichten in Kombination mit PBM besseres Wachstum beim Wels als ein vergleichbares kommerzielles Futter. In Futtern basierend auf einer einzigen Proteinquelle führte PM bei Wels und insbesondere bei Tilapia zu ähnlichem Wachstum verglichen mit marinem Fischmehl, wohingegen BSFM und PBM bei beiden Arten Wachstumsleistung beeinträchtigte. Meta-Analysen aller Versuche legen nahe, dass höherer Phosphor-, Kalium- und Magnesiumgehalt im Futter erhöhte Ausscheidung dieser Elemente in gelöster Form bedingt, was sie zu Zielnährstoffen in Aquaponikfuttern macht, während die Optimierung des Protein zu Energie-Verhältnisses im Futter die gelösten N:P- und N:K-Verhältnisse im RAS-Wasser verbessern kann. / By using the nutrient input from fish feeds for the combined production of fish and plants, aquaponic systems can be a sustainable extension of recirculating aquaculture systems (RAS). However, conventional aquaculture feeds are optimized for fish production and reduced environmental impact rather than aquaponics. Hence, RAS water is often characterized by deficiencies regarding its dissolved inorganic plant nutrient profile. Therefore, this thesis aimed to explore the effect of purposeful dietary protein choice on nutrient dynamics in RAS through four systematic feeding trials involving African catfish and Nile tilapia in which growth performance, dissolved inorganic nutrient concentrations in RAS water and solid fecal nutrient excretion were tracked. Focus was on sustainable alternative protein sources to marine fish meal and terrestrial plant proteins: black soldier fly larvae meal (BSFM), catfish by-product meal (CM), poultry by-product meal (PM) and poultry blood meal (PBM). Experimental diets including phosphorus-rich PM and CM supported increased excretion of soluble reactive phosphorus, produced the most favorable dissolved N:P ratios in RAS water when compared to a renowned hydroponic nutrient solution, and, combined with PBM, enabled better growth performance in African catfish than a comparable commercial diet. In single protein source diets, PM produced similar growth performance in African catfish and particularly Nile tilapia versus marine fish meal, whereas BSFM and PBM impaired growth performance in both species. Meta-analyses covering all trials suggest that higher dietary phosphorus, potassium and magnesium content leads to their increased excretion in dissolved form, making them target nutrients for aquaponic feed formulation, while the optimization of the dietary protein to energy ratio can further improve dissolved N:P and N:K ratios in RAS water.