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.
ABSTRACT. 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.Keywords: feeding schedule, circadian rhythm, feeding management, fish culture.Uma pequena alteração na estratégia alimentar em curso da tilápia pode prejudicar seu crescimento?RESUMO. O objetivo do presente trabalho foi responder a seguinte questão: uma pequena alteração na estratégia alimentar em curso da tilápia pode prejudicar seu crescimento? Na fase inicial do estudo, os peixes foram igualmente distribuídos e mantidos por duas semanas em quatro tanques. Nos tanques nº 1 e 2, a ração foi fornecida aos peixes em três refeições iguais às 8, 12 e 16h ou às 9, 13 e 17h, respectivamente. Nos tanques nº 3 e 4, havia apenas uma refeição diária às 9 ou 10h, respectivamente. Na segunda fase (8 semanas), os peixes do tanque nº 1 foram distribuídos em dez tanques de 100 L em dois grupos: o grupo 8-12-16, os peixes foram sempre alimentados às 8, 12 e 16h; e o grupo 8-12-16/9-13-17, os peixes foram alimentados às 8, 12 e 16h, nas primeiras quatro semanas, e às 9, 13 e 17h, nas quatro últimas semanas. Os peixes do tanque nº 2 foram distribuídos em cinco tanques de 100 L e suas refeições foram mantidas inalteradas. Os mesmos procedimentos foram utilizados nos tanques nº 3 e 4. O atraso de 1 h no fornecimento de ração reduziu significativamente a sobrevivência dos peixes.Palavras-chave: horário alimentar, ritmo circadiano, manejo alimentar, piscicultura.
ABSTRACT. 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 CaCO 3 ) 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. Desequilíbrios da relação dureza/alcalinidade da água e desempenho produtivo da tilápia do Nilo RESUMO. O presente estudo determinou os efeitos de diferentes relações dureza cálcica/alcalinidade total (DC/AT) da água de cultivo sobre o desempenho produtivo da tilápia do Nilo. Duas relações DC/AT foram testadas durante oito semanas em dois sistemas de cultivo: interno, com a utilização de 30 tanques de 100 L e externo, com 36 tanques de 250 L. As variáveis testadas foram a alcalinidade total da água (AT; 50 e 100 mg L -1 CaCO 3 ) e a relação DC/AT da água (1/2, 1/1 e 5/1). No sistema interno, os tanques com relação DC/AT de 5/1 apresentaram maior concentração de nitrogênio amoniacal total (NAT) que os tanques com relações DC/AT de 1/2 ou 1/1. No sistema externo, as maiores concentrações de NAT foram observadas nos tanques com relação DC/AT de 1/2. O solo dos tanques internos com relação DC/AT de 5/1 apresentaram maiores concentrações de carbono orgânico. Os efeitos deletérios da relação DC/AT de 5/1 sobre o desempenho zootécnico dos peixes cultivados foram maiores que aqueles associados à relação DC/AT de 1/2. Fator de conversão alimentar significativamente melhor foi observado nos tanques externos com relação DC/AT de 1/1, independentemente do nível de alcalinidade total da água.Palavras-chave: piscicultura, qualidade de água, Oreochromis nilocitus.
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 CaCO 3) 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.
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