The aim of this study was to compare two rearing systems for freshwater prawn Macrobrachium rosenbergii: one with use of a recirculating aquaculture system with biofilters (RAS) and another with use of microbial flocs (F). Thirty postlarvae of freshwater prawn with an initial average weight of 0.13 AE 0.05 g were randomly stocked in six experimental units with 0.20 m² and volume of 50 L. The experiment lasted thirty days. Dissolved oxygen, temperature and pH were monitored daily; ammonia concentration was determined three times per week; nitrite concentration, alkalinity and hardness were measured weekly. For the formation of microbial floc, molasses was used to keep the ammonia concentrations within safe levels for prawn farming. The variables of water quality remained within the suitable range for the production of the species, except for ammonia concentrations at the F treatment, which exceeded the safe levels. At the end of the experiment, the following parameters were evaluated: survival, specific growth rate, weight gain and feed conversion rate. Differences were found only in feed conversion rate with better values on RAS treatment. The microorganisms present in the RAS and F treatment were also evaluated. The densities of rotifers, amoebas and total bacteria were higher at the F treatment although the same organisms were found at the RAS treatment. The results of this study showed the possibility of rearing M. rosenbergii in biofloc system technology.

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ABSTRACT. The objective of this study was to evaluate the effect of stocking densities on productive performance of the freshwater prawn Macrobrachium rosenbergii in biofloc system. Experimental tanks (microcosms) with 0.20 m² area were used as experimental units. The tanks were connected to two 300 L matrix tanks (macrocosm) with biofloc technology, used as recirculating units. M. rosenbergii juveniles, with an initial weight of 0.315 ± 0.06 g and initial length of 33.34 ± 2.26 mm, was randomly distributed in the experimental tanks at different stocking densities (50, 100, 150, 200 and 250 ind m -²) and reared during 60 days. The total biomass at the end of the experiment was significant higher (P < 0.05) with the use of higher stocking density (250 ind m -2 ). However, prawns stocked at the density of 50 m -2 showed significant higher (P < 0.05) survival (73%) and significantly lower values (P < 0.05) for feed conversion rate (1.28). The different stocking densities evaluated did not affect the weight and length of prawns. The recommended density for growing M. rosenbergii in the biofloc system is 50 ind m -2 .

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This study evaluated the effects of feeding frequency and feeding rate on productive performance of hybrid surubims reared in cages with automatic feeding. Three feeding frequencies (6, 12 and 24 meals day -1 ), and two feeding rates (4% and 8% of body weight per day, BW day -1 ) were evaluated. Hybrid surubims (Pseudoplatystoma corruscans × Pseudoplatystoma fasciatum) with average weights of 24.20 ± 0.80 g were distributed in 18 cages of 1.0 m³ at a density of 60 fish m -3 . Fish were fed commercial ration containing 40% crude protein, and feeding took place at night using automatic feeders. The study lasted 47 days. With a feeding rate of 4% BW day -1 , the final weight (FW) of the surubims was higher when feed was supplied as 24 meals day -1 (66.92 g). However, using 8% BW day -1 , the FW was greater with a feeding frequency of 12 meals day -1 (106.90 g). Regardless of feed frequency, the values of daily weight gain and standard length of surubims were higher with the feeding rate of 8% BW day -1 . Therefore, the feeding rate of 8% BW day -1 , provided in 12 meals day -1 , provided better productive performance for hybrid surubims (Pseudoplatystoma corruscans × Pseudoplatystoma fasciatum) reared in cages. COMPARAÇÃO ENTRE DUAS TAXAS E TRÊS FREQUÊNCIAS ALIMENTARES PARA SURUBINS HÍBRIDOS CRIADOS EM TANQUE REDERESUMO -Este estudo avaliou os efeitos da frequência e taxa de alimentação sobre o desempenho produtivo de surubins híbridos criados em tanque rede. Três frequências (6, 12 e 24 refeições dia -1 ) e duas taxas de alimentação (4% e 8% do peso vivo por dia, PV dia -1 ) foram avaliadas. Híbridos de surubim (Pseudoplatystoma corruscans x Pseudoplatystoma fasciatum), com peso médio de 24,20 ± 0,80 g, foram distribuídos em 18 tanques rede de 1,0 m³ com densidade de 60 peixes m -³. Os peixes foram alimentados no período noturno por alimentadores automáticos, com ração comercial contendo 40% de proteína bruta. O estudo teve duração de 47 dias. Com a frequência de 4% PV dia -1 , o peso final (PF) dos surubins foi maior com o fornecimento da ração em 24 refeições dia -1 (66,92 g). Entretanto, usando 8% PV dia -1 o PF foi maior com a frequência de 12 refeições dia -1 (106,90 g). Independente da frequência alimentar, os valores de ganho de peso diário e comprimento padrão dos surubins foram maiores com a taxa de alimentação de 8% PV dia -1 . Assim, o fornecimento da ração com taxa alimentar de 8% PV dia -1 , dividida em 12 refeições dia -1 , proporcionou melhor desempenho produtivo para surubins híbridos (Pseudoplatystoma corruscans × Pseudoplatystoma fasciatum) criados em tanque rede.Palavras-chave: Manejo alimentar. Alimentação noturna. Pseudoplatystoma corruscans. Pseudoplatystoma fasciatum.