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The present work aimed to assess the partial replacement of artificial diets by wet bioflocs biomass in the culture of Nile tilapia juveniles. Fish were fed on different combinations of commercial dry diets (CD) and wet bioflocs biomass (BF), as it follows: 75% CD + 25% BF, 50% CD + 50% BF, and 25% CD + 75% BF, dry matter basis. There were also positive control tanks in which the fish received only commercial diet (100% CD), and three negative control tanks where the reductions of dry diets were not compensated by wet bioflocs biomass (75% CD, 50% CD, and 25% CD). Bioflocs were produced in one 500-L outdoor tank, which did not belong to the culture system, and it was called “separate BFT tank”, in which there was a daily adjustment of the C: N ratio of water to 15: 1, by the application of dry molasses to the water. There were no significant differences between the treatments for water pH, O2, TAN and NH3. Except by 25% CD, nitrite concentrations in water were lower in bioflocs tanks than in the artificial diet tanks. The final body weight of fish was significantly higher in tanks that received only dry diets (21.9 ± 6.4 g) than in tanks with a combination of 50% dry diet and 50% wet bioflocs biomass (10.4 ± 2.5 g; p < 0.05). It can be concluded that the impairment on the growth performance of tilapia submitted to feeding restriction is lessened if wet bioflocs biomass is provided to the animals. Besides, the total substitution of artificial diets for wet bioflocs biomass in clear-water tanks is unfeasible because it leads to higher rates of mortality of tilapia in a relatively short period.

The effects of supplying dried bioflocs biomass to Nile tilapia juveniles were investigated in the present work. Fish were stocked in experimental rearing tanks for eight weeks. Selected variables of water quality, growth performance and effluent quality were evaluated. Fish were given different combinations of artificial diets and biofloc biomass, in wet (in natura) or dry form. As the supply of artificial diet decreased, the allowance of biofloc biomass increased in the same proportion. Biofloc biomass was produced in two 500-L tanks that received daily applications of dry molasses to adjust the C: N ratio of the water to 15: 1. The concentration of nitrite in water was only reduced in the tanks receiving wet bioflocs. The fish growth performance was poorer in the tanks that received dried biofloc biomass than in the tanks with wet biofloc biomass. Given the lack of positive results, there is no justification to dry the biofloc biomass aiming at delivering it as a dry biomass to reared fish.

The present work determined the effects of water with unbalanced calcium hardness/total alkalinity (CH/TA) ratio on Nile tilapia growth performance. Two unbalanced CH/TA ratios were tested for 8 weeks using one indoor system with 30 circular polyethylene 100 L tanks and one outdoor system with 36 circular polyethylene 250 L tanks. The factors and their specific levels tested were the total alkalinity of water (TA; 50 and 100 mg L-1 CaCO3) and the CH/TA ratio of water (CH/TA; 1/2, 1/1 and 5/1). In the indoor system, the 5/1 CH/TA ratio tanks had higher total ammonia nitrogen (TAN) than the 1/2 or 1/1 CH/TA ratio tanks. In the outdoor system, higher concentrations of TAN were found in the 1/2 CH/TA ratio tanks. The soil of the 5/1 CH/TA ratio indoor tanks had higher concentrations of organic carbon than the 1/2 or 1/1 CH/TA ratio tanks. The detrimental effects of the 5/1 CH/TA ratio on fish growth performance were stronger than those associated with the 1/2 CH/TA ratio. A significantly better food conversion ratio was observed in the 1/1 CH/TA ratio outdoor tanks regardless of the TA level of the water.

The objective of the present work was to determine the effects of the interaction between feeding rate and area for periphyton in rearing aquaria for Nile tilapia. Twenty 25 L polyethylene outdoor aquaria were used to hold experimental fish. Three tilapia fingerlings (2.56  0.14 g) were stocked in each aquarium for five weeks (12 fish m-2). There were two different feeding rates (full and full minus 30%) and two submerged areas for periphyton development (59.4% and 96.5% of the aquarium surface area; n = 5). Final body weight, specific growth rate and yield in the 96.5%-area aquaria of fish submitted to 30% less feed were significantly higher than in the 96.5%-area aquaria submitted to full feeding rates. Fish growth in the restricted-feed aquaria was favored by their better water quality (higher pH and lower total ammonia nitrogen). There were negative effects on final body weight, SGR, yield and feed conversion ratio of fish in full-feed aquaria when the area for periphyton increased from 59.4 to 96.5%. It was concluded that the combination of restricted feeding rates with large substrate areas for periphyton growth results in better water quality for fish culture than the adoption of each management alone.O presente trabalho teve como objetivo determinar os efeitos da interação entre a taxa de arraçoamento e a área submersa para perifíton em aquários de cultivo de tilápia do Nilo. Foram utilizados 20 aquários de 25 L no trabalho. Três juvenis de tilápia (2,56  0,14 g) foram estocados em cada aquário por cinco semanas. Havia duas taxas de arraçoamento (cheia e cheia menos 30%) e duas áreas submersas para o desenvolvimento de perifíton (59,4 e 96,5% da área superficial do aquário; n = 5). O peso corporal final dos peixes nos aquários com 96,5% de área para perifíton e submetidos à taxa alimentar restritiva foram significativamente maiores que nos aquários com 96,5% de área e taxa alimentar padrão. O crescimento dos peixes nos aquários com arraçoamento restritivo foi favorecido pela melhor qualidade de água (maior pH e menos amônia). O crescimento e conversão alimentar dos peixes foram negativamente afetados nos aquários com 96,5% de área para perifíton e taxa de arraçoamento padrão. Concluiu-se que a combinação de taxas alimentares restritivas com a adoção de maiores áreas de substratos para o desenvolvimento de perifíton traz melhores resultados de qualidade de água que o emprego desses manejos de forma isolada.

The present study investigated the effects of different feeding schedules on certain variables of water quality and growth performance of Nile tilapia juveniles. Fifteen 25-L aquaria were used to hold the experimental fish population for six weeks. Five fingerlings (1.86  0.13 g) were stocked in each aquarium (200 fish m-3; n = 5). The diet provided to fish and the feeding rates adopted were the same for all fish. The daily ration was divided in four meals (8, 11, 13 and 16h). In the positive control group (25/25/25/25), the daily ration was equally divided in the four meals; in the negative control group (40/30/20/10), the daily ration was unevenly divided in a progressively decreasing fashion (40, 30, 20 and 10%) throughout the day; in the experimental group (10/20/30/40), the daily ration was unevenly divided in a progressively increasing fashion (10, 20, 30 and 40%) throughout the day. The feed conversion ratio results were better for 10/20/30/40 than for the other groups. The 10/20/30/40 feeding schedule probably best combined the dietary allowance for fish with the increase in water temperature during the day.O presente trabalho investigou os efeitos de diferentes programas alimentares sobre algumas variáveis de qualidade de água e de desempenho zootécnico da tilápia do Nilo. Foram utilizados 15 aquários de 25 L para manter a população experimental por seis semanas. Foram estocados cinco alevinos (1,86  0,13 g) em cada aquário (200 peixes m-3; n = 5). A dieta fornecida aos peixes e as taxas de arraçoamento adotadas foram as mesmas para todos os peixes. A ração diária foi dividida em quatro refeições (8, 11, 13 e 16h). No controle-positivo (25/25/25/25), a ração diária foi igualmente dividida nas quatro refeições; no controle-negativo (40/30/20/10), a ração diária foi desigualmente dividida de modo progressivamente decrescente (40, 30, 20 e 10%) ao longo do dia; no grupo experimental (10/20/30/40), a ração diária foi desigualmente dividida de modo progressivamente crescente (10, 20, 30 e 40%) ao longo do dia. Os resultados do fator de conversão alimentar foram melhores para 10/20/30/40 que para os outros grupos. O programa alimentar 10/20/30/40 foi aquele que provavelmente melhor combinou a oferta de dieta aos peixes cultivados com o aumento na temperatura da água durante o dia.

Present study investigated the effects of different feeding schedules on certain variables of water quality and growth performance of Nile tilapia juveniles. Fifteen 25-L aquaria were used to hold the experimental fish population for six weeks. Five fingerlings (1.86 ± 0.13 g) were stocked in each aquarium (200 fish m-3; n = 5). The diet provided to fish and the feeding rates adopted were the same for all fish. The daily ration was divided in four meals (8, 11, 13 and 16h). In the positive control group (25/25/25/25), the daily ration was equally divided in the four meals; in the negative control group (40/30/20/10), the daily ration was unevenly divided in a progressively decreasing fashion (40, 30, 20 and 10%) throughout the day; in the experimental group (10/20/30/40), the daily ration was unevenly divided in a progressively increasing fashion (10, 20, 30 and 40%) throughout the day. The feed conversion ratio results were better for 10/20/30/40 than for the other groups. The 10/20/30/40 feeding schedule probably best combined the dietary allowance for fish with the increase in water temperature during the day.

The aim of the present work was to answer the following question: can a small change in the tilapia’s on-going feeding strategy impair its growth? In the initial phase of the study, fish were evenly distributed and maintained for two weeks in four tanks. In tanks 1 and 2, the ration was given in three equal meals at 8, 12 and 16h or at 9, 13 and 17h, respectively. In tanks 3 and 4, there was only one daily meal at 9 or 10 o’clock, respectively. In the second 8-week phase, fish from tank 1 were distributed into two groups in ten 100-L tanks: the 8-12-16 group, in which fish were always fed at 8, 12 and 16h; and the 8-12-16/9-13-17 group, in which fish were fed at 8, 12 and 16h in the first four weeks and at 9, 13 and 17h in the last four weeks. Fish from tank 2 were allocated into five 100-L tanks and their mealtimes were maintained unchanged. The same procedures were used in tanks 3 and 4. The delay of one hour in the allowance of the artificial diet has significantly reduced fish survival.

Present study investigated the effects of different feeding schedules on certain variables of water quality and growth performance of Nile tilapia juveniles. Fifteen 25-L aquaria were used to hold the experimental fish population for six weeks. Five fingerlings (1.86 ± 0.13 g) were stocked in each aquarium (200 fish m-3; n = 5). The diet provided to fish and the feeding rates adopted were the same for all fish. The daily ration was divided in four meals (8, 11, 13 and 16h). In the positive control group (25/25/25/25), the daily ration was equally divided in the four meals; in the negative control group (40/30/20/10), the daily ration was unevenly divided in a progressively decreasing fashion (40, 30, 20 and 10%) throughout the day; in the experimental group (10/20/30/40), the daily ration was unevenly divided in a progressively increasing fashion (10, 20, 30 and 40%) throughout the day. The feed conversion ratio results were better for 10/20/30/40 than for the other groups. The 10/20/30/40 feeding schedule probably best combined the dietary allowance for fish with the increase in water temperature during the day.