An economical and efficient approach to reduce the impact of P discharge by aquaculture industry is to adjust the P level in fish feeds to the precise nutrient requirement at different growth stages in a digestible nutrient basis. However, P requirement seems to be species specific and affected by several physiological, dietary and environmental factors. Based on the importance of tambaqui (Colossoma macropomum) to Latin American aquaculture, we designed a 63-day trial to evaluate the effect of available P (AP) levels on growth, nutrient digestibility, haematology and blood biochemical parameters, carcass proximate composition and bone mineralization. Quadruplicate groups of tambaqui juveniles (144 AE 2.0 g) were fed five isonitrogenous (278 g kg À1 digestible protein) and isocaloric (13.5 Mj DE kg À1 ) diets containing graded AP levels (3.0, 5.6, 7.5, 9.1 and 11.0 g kg À1 ) following a completely randomized design. Dicalcium phosphate (DCP) was used as the main P source. No mortalities and signs of P deficiency were observed among the dietary treatments. A remarkably high P digestibility was observed in all plantbased diets with a tendency of decreasing P digestibility with the increase in total P levels. Tambaqui seems to be able to grow well without inorganic P supplementation during the trials; however, this species required 7.0 g AP kg À1 diet for proper bone mineralization. P supplementation had a limited effect on haematology and blood biochemistry of tambaqui. Ecological implications of natural feeding habit and evolutionary position of this species are further discussed, and new hypothesis are drawn based on our results.

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Based on the importance of tambaqui, Colossoma macropomum, for Latin American aquaculture and the digestibility of minerals for the production of sustainable aquafeeds, we designed a series of trials to determine the apparent digestibility coefficients (ADCs) of phosphorus, calcium, magnesium, manganese, and zinc from six protein sources: soybean meal (SBM), corn gluten meal 60 (CGM60), cottonseed meal 40, fishmeal (FM), poultry byproduct meal (PBM), and meat and bone meal (MBM); four cereal grain products: corn, wheat middlings, broken rice (BR), and rice bran (RB); and dicalcium phosphate (DCP). Considerable variation in the ADCs of minerals was observed among the feed ingredients. In general, CGM60, PBM, and RB tended to show the highest ADC values, while SBM, MBM, DCP, and BR showed the lowest ADC values. ADC‐P was markedly lower in animal protein sources and the phosphate source (DCP), while high P digestibility was observed for plant protein sources and cereal grain products. Interestingly, tambaqui seems to be able to digest and absorb minerals from plant ingredients more efficiently than animal proteins and DCP. In light of the correlation between nutrient levels and the ADCs of minerals, physiological mechanisms that regulate mineral uptake, and the nutritional ecology of the species, we hypothesize that tambaqui are able to digest minerals from plant proteins with high efficiency.

Summary Determining the ingredients and/or digestibility of a diet is one of the most important steps in fish nutrition for accurate diet formulation. Additionally, the use of digestible nutrient data in fish feed formulation can reduce the environmental impact of aquaculture. To properly determine the nutrient digestibility (ADC) of a feed ingredient and/or compound diets, an accurate faeces‐collecting method should be used to provide reliable information on the digestion capacity of a determined species. Thus, a series of two trials were performed aiming to evaluate and standardize a faeces‐collecting method for Colossoma macropomum. Faeces from all groups were collected using one of the methods. In trial 1, two faeces‐collecting methods (sedimentation and dissection) were evaluated using 80 juveniles (170 g average weight) randomly assigned into four 310‐L aquaria. In trial 2, 135 juveniles (300 g average weight) were randomly distributed into nine 310‐L aquaria and fed a control diet (without binder) and diets containing a dietary binder at 0, 2 and 4 g kg−1 diet aiming to test the effect of binder inclusion on the ADC of nutrients. Fish were fed in triplicate groups per diet. Results showed that the dissection method provided the lowest ADC values for dry matter, phosphorus and gross energy. ADC of dry matter tended to decrease up to 5 h (305 min) of faeces immersion and seem to stabilize afterwards. Using 4 g kg−1 of dietary binder tended to reduce the leaching of DM, and no effect was observed on the protein digestibility. Phosphorus was the nutrient most prone to leaching in faeces. Faeces collection within 1 h is recommended in the sedimentation method in C. macropomum digestibility studies; the use of dietary binder at 4 g kg−1 may be a useful approach to reduce nutrient leaching in the faeces.

The expansion in the market of ornamental fish depends on the intensification of production systems and the generation of appropriate technologies. Therefore, it is necessary to know the nutritional requirements of each species for the formulation of nutritionally balanced diets. A 30-day feeding trial was undertaken to evaluate the effects of different dietary digestible protein to energy ratio in diets for Betta splendens fingerlings. Fifty-six all-male B. splendens with 1.03 ± 0.11 g average weight were randomly stocked into 56 1L-aquaria in a completely randomized design with a 2 x 4 factorial arrangement, comprising eight treatments and seven replication. Each fish was considered an experimental unit. Diets were formulated to contain 28.0, 35.0, 42.0 and 49.0% DP and 3,600 and 3,200 kcal/kg DE. The growth parameters evaluated in this trial were weight gain (WG), feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER) and specific growth rate (SGR). No difference (P > 0.05) was observed for WG, FCR and SGR. However, a higher FI was observed for fish fed diets containing 42.0% DP (P < 0.05). A positive effect of DP and DE on PER was observed in this study. Generally, according to the increase of DE levels, a reduction on PER was observed. Based on this experimental condition, we recommend the use of 28.0% DP and 3,200 kcal/kg DE in diets for B. splendens. Index terms:Protein requirement, ornamental fish, carcass composition, energy requirement, growth. RESUMOA expansão no setor produtivo de peixes ornamentais depende da intensificação dos sistemas de produção e da geração de tecnologias adequadas. Por isso, é necessário o conhecimento das exigências nutricionais de cada espécie para a formulação de rações nutricionalmente adequadas. Neste estudo, objetivou-se avaliar as diferentes relações energia:proteína digestível em dietas para alevinos de Betta splendens. O experimento teve a duração de 30 dias, sendo utilizados 56 alevinos machos de B. splendens com peso médio inicial de 1,03 ± 0,11 g. O delineamento experimental utilizado foi o inteiramente casualisado em arranjo fatorial, sendo composto por oito tratamentos e sete repetições, considerando-se um peixe como uma unidade experimental. Foram formuladas dietas práticas, cujos níveis de proteína digestível foram 28,0; 35,0; 42,0 e 49% e os níveis de energia digestível de 3.200 e 3.600 kcal/kg. Os parâmetros de desempenho produtivo avaliados foram: ganho em peso (GP), consumo de ração aparente (CRA), conversão alimentar aparente (CAA), taxa de eficiência protéica (TEP) e taxa de crescimento especifico (TCE). Não houve diferença significativa entre os tratamentos para GP, CAA, TCE, entretanto foi observado maior CRA para o nível de PD de 42% (P<0,05). A TEP apresentou diferença significativa, de maneira que quanto maior o nível de energia digestível menor a taxa de eficiência protéica. Com base nas condições experimentais deste estudo e na taxa de eficiência protéica, o melhor nível de PD e ED para melhor taxa de eficiência protéi...

The optimal dietary digestible protein to energy ratio is critical for the success of fish farming. Considering that it provides the proper development of the animals, this study was undertaken to evaluate the effects of different dietary digestible protein to energy ratio in diets for goldfish fingerlings. Diets were formulated to contain 28.0, 35.0, 42.0 and 49.0% DP and 3,600 and 3,200 kcal/ kg. The growth parameters evaluated were daily weight gain (DWG), feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER), protein productive value (PPV) and energy retention ratio (ERR) and specific growth rate (SGR). Regardless FI, all the parameters were affected by protein and energy levels and interaction between both factors was observed. The second-order polynomial equation best fitted to the DWG, SGR, FCR, PER and ERR with estimated requirement values of 38.81, 38.85, 41.05, 41.80 and 39.39% DP, respectively, at the 3,200 kcal/kg. A second-order polynomial model was significant only for the ERR data at the 3,600 kcal/kg with an estimated requirement value of 36.45% DP. Generally, fish fed diets containing 3,200 kcal/kg had better growth performance than fish fed 3,600 kcal/kg (P<0.01), indicating a higher feed efficiency. A 3,200 kcal/kg diet seems to be the proper DE level for meeting goldfish requirement for highest weight gain. Based on this experimental condition, we recommend the use of DP levels between 38.0-40.0% in diets for goldfish with 3,200 kcal/kg or a dietary protein to energy ratio between 119-125 mg/ kcal DE.Index terms: Energy requirement, feed intake, growth protein requirement, ornamental fish. RESUMOA ótima relação energia/proteína é importante para o sucesso da piscicultura. Considerando que a mesma fornece o adequado desenvolvimento dos animais, este estudo foi realizado para avaliar a relação energia/proteína digestível ótima para alevinos de kinguio. Dietas foram formuladas para conter 28,0; 35,0; 42,0 e 49,0% PD e 3600 e 3200 kcal/kg. Foram avaliados: ganho de peso diário (GPD), consumo de ração aparente (CRA), conversão alimentar aparente (CAA), taxa de eficiência protéica (TEP), valor produtivo protéico (VPP), taxa de retenção de energia (TRE) e taxa de crescimento especifico (TCE). Com exceção do CRA, todos os parâmetros foram afetados pelos níveis de proteína e energia e interação entre os dois fatores foram observados. O modelo que melhor se ajustou aos parâmetros GPD, TCE, CAA, TEP e TRE foi o polinomial de segunda ordem com valores de exigência de 38,81; 38,85; 41,05; 41,80 e 39,39% DP, respectivamente, para o nível de 3200 kcal ED/kg. O modelo polinomial de segunda ordem foi significativo apenas para os dados de TRE no nível de 3600 kcal ED/kg, com valor de exigência 36,45% PD. Os peixes alimentados com dietas contendo 3200 kcal/kg apresentaram melhor desempenho de crescimento do que os alimentados com 3600 kcal/kg (P<0,01), indicando uma maior eficiência alimentar. 3200 kcal/kg ED parece ser o nível adequado encontrado para kinguio para maior ganho d...