We aimed in this study utilize environmental indicators as a quantitative method to evaluate and discuss the nitrogen (TN) and phosphorus (TP) flux by a production stage grow-out (termination) of Nile tilapia (Oreochromis niloticus) in fishpond. The TN and TP load, the mass balance, the input of TN and TP via feed and the converted nutrients in fish biomass are the environmental indicators applied in this study. During the production cycle (128 days), the system exported 15,931 g TN and 4,189 g TP that were related to the amount of feed supplied (r Pearson = 0.8825 and r = 0.8523, respectively), corroborated by the feed conversion ratio (1.61:1). The indicators showed that 26% TN and 45% TP were reversed into fish biomass, 62% TN and 40% TP were retained in the fishpond, and 12% TN and 15% TP were exported via effluent. The largest contribution of nutrients generated by the system and exported via effluent was observed in phase III and IV. This result is supported by the feed conversion ratio 2.14 and 2.21:1 obtained at this phase, a fact explained by the amount of feed offered and the fish metabolism. Application of environmental indicators showed to be an efficient tool to quantify flux of TN and TP produced during the grow-out period of Nile tilapia and therefore, guide management practices more sustainable. Concerning the environmental sustainability of the activity the implementation of best management practices such as the better control of the feed amount offered would lead to a smaller loss of TN and TP to the water. Furthermore, the use of better quality feeds would allow greater nutrient assimilation efficiency.Keywords: environmentally sustainable management, nutrients load, mass balance, fish-farming, Oreochromis niloticus. Fluxo de nitrogênio e fósforo na produção de tilápia-do-nilo (Oreochromis niloticus) a partir da aplicação de indicadores ambientais ResumoNós objetivamos neste estudo, utilizar indicadores ambientais como método quantitativo para avaliar e discutir sobre o fluxo de nitrogênio (TN) e fósforo (TP) na etapa final de crescimento (terminação) de tilápia-do-nilo (Oreochromis niloticus) em viveiro escavado. A carga de TN e TP, o balanço de massa, a entrada de nutrientes via ração e o TN e TP convertido em biomassa de peixe foram os indicadores ambientais utilizados neste estudo. Durante o ciclo produtivo (128 dias), o sistema exportou 15.931 g NT e 4.189 g PT os quais foram relacionadas às quantidades de alimento fornecido (r Pearson = 0,8825 e r = 0,8523, respectivamente), corroborada pela conversão alimentar (1,61:1). Os indicadores evidenciaram que 26% NT e 45% PT foram revertidos em biomassa de peixe, 62% NT e 40% PT ficaram retidos no viveiro e 12% NT e 15% PT foram exportados via efluente. O maior aporte de nutrientes gerado pelo sistema e exportado via efluente foi verificado nas fases III e IV. Este resultado é corroborado pelas taxas de conversão alimentar de 2,14 e 2,21:1 obtida nestas fases, fato explicado pela quantidade de ração ofertada e pelo metabolismo dos peixe...

The concern in mitigating the negative impact generated by the discharge of nutrients in the receiving water body is a challenge for the sustainable development of Brazilian fish farms. Thus, the purpose of this study was to evaluate the water quality and environmental impact caused by trout farming system effluent with focus on discharge of phosphorus. Sampling was performed on a weekly basis in triplicate from September to November 2010. Sample sites were distributed according to the water flow: upstream from trout farming system, water supply, effluent, artificial wetland, mixing zone and downstream (60 m from effluent). In the field, pH, conductivity, dissolved oxygen, water temperature and turbidity were measured. In laboratory, nitrogen and phosphorus series, chlorophyll a, total solids suspended and their organic and inorganic fractions were analyzed. For the good growth of trout in production system, the abiotic factors described in the water quality monitoring demonstrated acceptable values. Environmentally, after passing through the production system and artificial wetland, there was an increase in concentrations of total phosphorus, total nitrogen, orthophosphate, ammonium, chlorophyll a, total solids suspended and their organic and inorganic fractions (P < 0.05). These results are related with the quality of feed, feeding management and the inefficiency of the artificial wetland. Therefore, it is necessary to use best quality feed to meet the nutritional requirements of trout, maintaining an optimal feed conversion and reducing pollution generated by effluent.

Aim: The mass balance has recently been applied in Brazilian aquaculture. In relation to trout farming, few studies have used this methodology as environmental indicator, especially when considering each development stage of fish. The daily mass balance allows an estimate of nutrients discharge, because the sampling effort over 24 hours enables to monitor the variations throughout the day. This study aimed to identify the breeding sector (fingerlings, juveniles and adults) in trout farming contributes with the great discharge of phosphorus and nitrogen in the effluent. Methods The concentrations of total phosphorus (TP), orthophosphate (PO4-P), total nitrogen (TN) and ammonium (NH4-N) were determined in affluent and effluents of the production system. The environmental indicators were calculated based on the values of nutrients loads and by quantifying the daily discharge of nutrients from the mass balance method. Results Over the 24 hours, the trout farming exported an average of 0.26 kg TP, 0.11 kg PO4-P, 3.11 kg TN and 0.18 kg NH4-N. The discharge of phosphorus and nitrogen in the effluent was higher at night associated to feeding management (hours and feeding frequency) and the nocturnal habits of trout. The juvenile and adult sectors accounted for the greatest contribution of these nutrients, related the largest fish biomass and metabolism, supported by the feed conversion ratio of 1.95:1 and 2.01:1, respectively. Conclusion In order to reduce exports of phosphorus and nitrogen there is a need to adequate the feeding management (feeding frequency from two to four times per day according to the trout development stage; carry out feeding in times close at twilight due to the nocturnal habits of this specie; reduce excess of ration offered and use good quality ration considering the distinct nutritional requirements of each trout stage of development). Besides the mass balance, the feed conversion ratio is also an efficient tool to detect the efficiency of feed utilization; therefore, it is proposed its use as environmental indicator, aiming the aquaculture environmental sustainability.

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