Environmental indicators in effluent assessment of rainbow trout (Oncorhynchus mykiss) reared in raceway system through phosphorus and nitrogen

Abstract

The phosphorus and nitrogen discharge via effluent of intensive trout farming system was quantified through the use of environmental indicators. The nutrient loads, the mass balance, the estimated amount of nutrients in feed and the amount of nutrients converted in fish biomass were calculated based on the concentrations of phosphorus (P) and nitrogen (N) in the feed and in the water. Of the offered feed, 24.75 kg were available as P and 99.00 kg as N, of these, 9.32 kg P (38%) and 29.12 kg N (25%) were converted into fish biomass and 15.43 kg P (62%) and 69.88 kg N (75%) were exported via effluent. The loads and the mass balance show the excessive discharge of nutrients via effluent, corroborated by the feed conversion ratio (2.12:1) due to the low efficiency of feed utilization, therefore, it is proposed the use of this zootechnical parameter as environmental indicator. In addition, feed management practices are not adequate, highlighting the low frequency of feeding during the day, excessive amount and low quality of feed offered. These results demonstrate the need for adequate feed management and the need for careful monitoring of effluent.Keywords: nutrients loads, mass balance, feed conversion ratio, eutrophication, Oncorhynchus mykiss (Walbaum).Indicadores ambientais na avaliação de efluentes de truta arco-íris (Oncorhynchus mykiss) criados em sistema de raceway através do fósforo e nitrogênio Resumo A descarga de fósforo e nitrogênio via efluente do sistema intensivo de truticultura foi quantificada através da utilização de indicadores ambientais. As cargas de nutrientes, o balanço de massa, a quantidade estimada de nutrientes na ração e a quantidade de nutrientes convertidos em biomassa de peixes foram calculados com base nas concentrações de fósforo (P) e nitrogênio (N) na ração e na água. Da ração oferecida, 24,75 kg estavam disponíveis como P e 99,00 kg como N, destes, 9,32 kg de P (38%) e 29,12 kg de N (25%) foram convertidos em biomassa de peixe e 15,43 kg P (62%) e 69,88 kg N (75%) foram exportados via efluente. As cargas e o balanço de massa mostram a descarga excessiva de nutrientes via efluente, corroborado pela taxa de conversão alimentar (2,12:1), devido à baixa eficiência na utilização da ração, portanto, propõe-se a utilização deste parâmetro zootécnico como indicador ambiental. Além disso, as práticas de manejo alimentar não são adequadas, destacando a baixa frequência de alimentação durante o dia, quantidade excessiva e baixa qualidade da alimentação ofertada. Esses resultados demonstram a necessidade de manejo alimentar adequado e de monitoramento do efluente.Palavras-chave: cargas de nutrientes, balanço de massa, taxa de conversão alimentar, eutrofização, Oncorhynchus mykiss (Walbaum).

Nitrogen and phosphorus flux from the production of Nile tilapia through the application of environmental indicators

“…In Brazil, indicators proposed by Boyd and Queiroz (2001) and Boyd et al (2007) were evaluated by Moraes et al (2016), in a trout farming system (Oncorhynchus mykiss) and was observed that from the total N and P offered feed, 25% of N and 38% of P were converted into fish biomass and 75 of N and 62% of P were exported via effluent. These authors attributed the values to the management practices, such as excessive amount and low quality of feed offered.…”

“…In Brazil, although scarce studies performed in trout farming (Caramel et al, 2014;Moraes et al, 2015Moraes et al, , 2016, in bullfrog farming (Borges et al, 2012;Mercante et al, 2014) and in polyculture system (tilapia and shrimps) (Araújo-Silva et al, 2014), showed that environmental indicators can be a useful tool for characterizing the impact, since it allows the comparison of different systems, methods of creation, evaluation of the effectiveness of management practices used in the production system, descriptions of general standards and as reference values (Boyd et al, 2007;Kimpara et al, 2010).…”

Influence of trout farm effluents on selected oxidative stress biomarkers in larvae of Ecdyonurus venosus (Ephemeroptera, Heptageniidae)

“…The products of fish metabolism, remains of food, and dissolved nutrients from fish farms are the main pollutants released by them [41], and they represent one of the most frequent problems in pollution of the recipient [42]. Only about 30% of fish food is transformed into biomass of the object of aquaculture, while the remainder flows into the recipient and constitutes the most important parameter when considering the influence of a fish farm on an aquatic environment [43,44]. In view of this and the fact that certain amounts of phosphorus and nitrogen (which fish food contains) can cause eutrophication, in the present study, for comparison of the effects of trout farms with different production capacities, we selected the same type of fish food (see Materials and Methods).…”

Artificial floating islands as a tool for the water quality improvement of fishponds

“…The feeding practices necessary to sustain semi-intensive and intensive fish farming systems contribute to the input of large amounts of nutrients into the water. No more than 25% of N and 30% of P added to fishponds as feed are converted into fish biomass (Moraes et al, 2016;Chatvijitkul et al, 2017;David et al, 2017a;2017b;Osti et al, 2018a). Additionally, overfeeding or the use of unbalanced feed reduces the absorption of nutrients by fish, which can result in excess of organic matter and nutrients in production systems, with direct consequences on water quality, favoring their assimilation by phytoplankton and aquatic macrophytes.…”