The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carboh... more The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g−1) were formulated incorporating WDM at 0, 100, 200 and 300 g kg−1 levels as partial substitutes for soybean meal (SBM). These were designated D0 [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg−1 diet], D1 (279 g CP and 446 g CHO kg−1 diet), D2 (207 g CP and 495 g CHO kg−1 diet) and D3 (175 g CP and 578 g CHO kg−1 diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different (P > 0.05). Protein efficiency rate (PER) was lowest in diet D0 and increased with decrease of SBM content (D1–D3). A significant increase in whole body lipid content was recorded in fish fed diets D2 and D3. Results showed that WDM could be a substitute for SBM up to 300 g kg−1 in practical Nile tilapia diets without compromising growth.
The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean me... more The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean meal in a practical diet formulated to contain 28% crude protein, 7.50% lipid and 15 kJ gross energy g−1. Soybean meal was replaced by 0%, 10%, 20% and 30% of UM (diets U0, U1, U2 and U3, respectively). The feeding experiment was carried out in an open circulation system. Each diet treatment was applied to triplicate groups of 30 fish (21.37 ± 0.193 g average wet weight) per tank (400 L) arranged in a completely randomized design. The fish were hand fed to satiation four times daily between 07.00 and 18.00 hours for 75 days. There were no significant differences (P > 0.05) in growth performance among fish fed with diets U0, U1 and U2. However, fish fed diet U3 had significantly lower growth (P < 0.05) than those fed diets U0, U1 and U2. Fish fed the control diet (U0) and diets including 10% and 20% UM had significantly (P < 0.05) better daily weight gain, relative growth weight, specific growth weight and protein efficiencies ratio than those fed with diet U3. Feed conversion ratio increased with increasing UM content, but only the value found in fish fed with diet U3 differed significantly (P < 0.05) from all other treatments. Survival rates ranged between 91.11% and 93.33%. No feed-related mortality was observed during the entire experimental period. Apparent protein digestibility (APD) of diets ranged from 87.06 to 69.91% and was lowest for fish fed with diet U3. In general, APD values decreased with increasing inclusion levels of UM, explained by the increase of anti-nutritional factors and high non-digestible fibre content. Compared to the control diet (U0), fish fed diets containing high levels of UM had lower levels of carcass lipid and higher levels of carcass moisture. Results show that this product can be included by up to 20% in practical male Nile tilapia diets with no detrimental effects.
The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess d... more The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess during the hours of light, following their exposure to five thermal regimes fluctuating around the thermal optimum for growth (Topt = 30° C) over the diel cycle of day (light, L) and night (dark, N), i.e. 27° C(L):33° C(N), 28·5° C(L):31·5° C(N), 30° C(L):30° C(N), 31·5° C(L):28·5° C(N) and 33° C(L):27° C(N) (two replicates per treatment, six weeks' rearing, growth measurements at weekly intervals). A model constructed with a stepwise multiple-regression analysis accounted for 87·4% of the variation of the specific growth rate (G, % M day−1) from the variations of wet mass (M), the extent of the thermal fluctuation (FT) and their interactions, i.e. log10G = 1·7686 − 0·2136 log10M + 0·0806 [log 10M× log 10 (1 + FT)] − 0·0394 [log10M× log 10 (1 + FT)]2. Based on this model, the thermal fluctuation that produces the fastest growth ( ,°C) decreases in a curvilinear way, from 5·1° C at 20 mg to c. 0·7° C at 20 g. Thermal regimes that produce the slowest growth also produce the highest size heterogeneity. Functional hypotheses behind the size-dependent effects of thermal fluctuations are discussed, together with their implications in natural habitats and aquaculture systems with in different contexts of food availability.
The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carboh... more The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g−1) were formulated incorporating WDM at 0, 100, 200 and 300 g kg−1 levels as partial substitutes for soybean meal (SBM). These were designated D0 [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg−1 diet], D1 (279 g CP and 446 g CHO kg−1 diet), D2 (207 g CP and 495 g CHO kg−1 diet) and D3 (175 g CP and 578 g CHO kg−1 diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different (P > 0.05). Protein efficiency rate (PER) was lowest in diet D0 and increased with decrease of SBM content (D1–D3). A significant increase in whole body lipid content was recorded in fish fed diets D2 and D3. Results showed that WDM could be a substitute for SBM up to 300 g kg−1 in practical Nile tilapia diets without compromising growth.
The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean me... more The use of green algae ulva meal (UM) (Ulva rigida) was evaluated as a replacement for soybean meal in a practical diet formulated to contain 28% crude protein, 7.50% lipid and 15 kJ gross energy g−1. Soybean meal was replaced by 0%, 10%, 20% and 30% of UM (diets U0, U1, U2 and U3, respectively). The feeding experiment was carried out in an open circulation system. Each diet treatment was applied to triplicate groups of 30 fish (21.37 ± 0.193 g average wet weight) per tank (400 L) arranged in a completely randomized design. The fish were hand fed to satiation four times daily between 07.00 and 18.00 hours for 75 days. There were no significant differences (P > 0.05) in growth performance among fish fed with diets U0, U1 and U2. However, fish fed diet U3 had significantly lower growth (P < 0.05) than those fed diets U0, U1 and U2. Fish fed the control diet (U0) and diets including 10% and 20% UM had significantly (P < 0.05) better daily weight gain, relative growth weight, specific growth weight and protein efficiencies ratio than those fed with diet U3. Feed conversion ratio increased with increasing UM content, but only the value found in fish fed with diet U3 differed significantly (P < 0.05) from all other treatments. Survival rates ranged between 91.11% and 93.33%. No feed-related mortality was observed during the entire experimental period. Apparent protein digestibility (APD) of diets ranged from 87.06 to 69.91% and was lowest for fish fed with diet U3. In general, APD values decreased with increasing inclusion levels of UM, explained by the increase of anti-nutritional factors and high non-digestible fibre content. Compared to the control diet (U0), fish fed diets containing high levels of UM had lower levels of carcass lipid and higher levels of carcass moisture. Results show that this product can be included by up to 20% in practical male Nile tilapia diets with no detrimental effects.
The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess d... more The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess during the hours of light, following their exposure to five thermal regimes fluctuating around the thermal optimum for growth (Topt = 30° C) over the diel cycle of day (light, L) and night (dark, N), i.e. 27° C(L):33° C(N), 28·5° C(L):31·5° C(N), 30° C(L):30° C(N), 31·5° C(L):28·5° C(N) and 33° C(L):27° C(N) (two replicates per treatment, six weeks' rearing, growth measurements at weekly intervals). A model constructed with a stepwise multiple-regression analysis accounted for 87·4% of the variation of the specific growth rate (G, % M day−1) from the variations of wet mass (M), the extent of the thermal fluctuation (FT) and their interactions, i.e. log10G = 1·7686 − 0·2136 log10M + 0·0806 [log 10M× log 10 (1 + FT)] − 0·0394 [log10M× log 10 (1 + FT)]2. Based on this model, the thermal fluctuation that produces the fastest growth ( ,°C) decreases in a curvilinear way, from 5·1° C at 20 mg to c. 0·7° C at 20 g. Thermal regimes that produce the slowest growth also produce the highest size heterogeneity. Functional hypotheses behind the size-dependent effects of thermal fluctuations are discussed, together with their implications in natural habitats and aquaculture systems with in different contexts of food availability.
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