Thesis (Ph.D.) - Cairo University - Faculty of Agriculture - Department of Animal Production

This study was performed through two experiments, experiment (I) was conducted to assess the ability to culture eel fish under biofloc system and the effect of feeding dry diet on feeding behavior and health status of European eel (Anguilla anguilla). Two diets of different protein levels were examined (T1: 35%, T2: 47%). Six circular polyethylene tanks (working capacity of 300 L) were used as experimental units, with three replicates per treatment. Each tank was stocked with ten fish with a total biomass ranged between 572-578 g. Eels were observed to consume dry pellets successfully from the water surface and showed ability for floc grazing after the first month of the experiment that lasted for 66 days. High-protein level increased water total suspended solids (TSS) values (p<0.05) and negatively altered gills morphology. Intestinal villi length, width, and absorption surface were increased (p<0.05) in fish fed low-protein diet. Liver antioxidant enzymes did not differ significantly among treatments. Higher crude protein (14.73%) and ash content (2.15%) were recorded for T1 (p<0.05). The results suggested the eel had the ability to graze floc particle aggregates without impacts to its health status when feeding on low-protein diet. Biofloc technology could be a promising sustainable system for all industrial sectors of European eel. Experiment (II) was designed to manipulate dietary carbon content to maintain C/N ratio of 10:1, using low -protein diets in parrellel with no addition of external carbon source.The effect on growth performance, water quality, body chemical composition and health status of common carp (Cyprinus carpio ) under biofloc system during nursery phase was recorded in comparison with the to control that supplemented with external carbon source .Three isonitrogenous diets (25%), and different lipid levels (3, 6 and 9%) namely, 25 L3, 25 L6 and 25 L9 were used to design three experimental treatments plus the control diet (35% CP, 3% lipid) namely, 35 L3. The experimental design was completely randomized, with four treatments each administered to three replicates in 12 circular plastic tanks (water capacity of 70 L). Early fingerlings of 6.58 ± 0.06 g (Mean ± SD) were distributed at a stocking density of 20 fish / tank. Growth performance and feed utilization parameters did not differ significantly among treatment groups

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