Abstract
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.
Highlights
Aquaculture is a growing economic sector, responsible by producing healthy food and nutritionally rich in protein
Nile tilapia production after 128 days was of 11,013 kg ha-1 of fish biomass and was used a total of 18 t ha-1 of feed, and the feed conversion ratio (FCR) of the production was 1.63:1
The better utilization of nutrients from feed by tilapia occurred at the beginning of the grow-out period, period when smaller quantities of feed were offered (112 kg ha d–1) and recorded the smaller nutrient loads (TN and tons of phosphorus (TP)) exported via effluent
Summary
Aquaculture is a growing economic sector, responsible by producing healthy food and nutritionally rich in protein. The magnitude of the aquaculture impacts depends on the produced species, the production method, the hydrography of the region, the type of feed provided and management practices (Macedo and Sipaúba‐Tavares, 2005; Cao et al, 2007). Management practices such as fertilization of ponds, increases of the water flow to prevent algal blooms and the quality and quantity of feed promote the increase of the nutrients in the water. A small part of these nutrients entering via the feed is effectively reversed into fish biomass; the remainder is retained in the sediment or exported via effluent
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