Abstract
Recirculating aquaculture systems (RAS) are a new alternative to traditional aquaculture approaches, allowing full control over the fish production conditions, while reducing the water demand. The reduction of water exchange leads to an accumulation of dissolved organic matter (DOM) that can have potential effects on water quality, fish welfare and system performance. Despite the growing awareness of DOM in aquaculture, scarce scientific information exists for understanding the composition and transformation of DOM in RAS. In this study, a non-targeted approach using ultra-performance liquid chromatography coupled to a hybrid quadrupole-time of flight mass spectrometer (UPLC-QTOF-MS) was used to characterize compositional changes of low molecular weight (LMW) DOM in RAS, when operated under two different feed types. A total of 1823 chemicals were identified and the majority of those contained a CHON chemical group in their structure. Changes in the composition of LMW-DOM in RAS waters were observed when the standard feed was switched to RAS feed. The DOM with the use of standard feed, consisted mainly of lignin/CRAM-like, CHO and CHOS chemical groups, while the DOM that used RAS feed, was mainly composed by unsaturated hydrocarbon, CHNO and CHNOS chemical groups. The Bray-Curtis dissimilarity cluster demonstrated differences in the composition of DOM from RAS and was associated to the type of feed used. When the RAS feed was used, the Kendrick mass defect plots of –CH2- homologous units in the pump-sump (after the water treatment) showed a high removal capacity for CHNO, CHNOS and halogenated chemicals with high Kendrick mass defect, KMD > 0.7. To our knowledge, this is the first report of LMW-DOM characterization of RAS by high-resolution mass spectrometry (HRMS).
Highlights
Fish is a primary source of animal proteins, micronutrients and essential fatty acids whose demand is increasing due to the rapid human population growth (Bogard et al, 2015; Thilsted et al, 2016)
Other challenges of dissolved organic matter (DOM) accumulation in Recirculating aquaculture systems (RAS) include the contamination of the fish environment, which further risks the welfare of the fish (Bregnballe, 2015), while the deterioration of water quality increases the need for further water treatment processes, and leads to higher production costs (Cai and Leung, 2017; Subasinghe, 2017)
The water quality parameters, including temperature, pH, oxygen and salinity, reflected the commercially relevant conditions used during the production of Atlantic salmon post-smolt (Kroglund et al, 2008; Elliott and Elliott, 2010; Thorarensen and Farrell, 2011)
Summary
Fish is a primary source of animal proteins, micronutrients and essential fatty acids whose demand is increasing due to the rapid human population growth (Bogard et al, 2015; Thilsted et al, 2016). The lack of data concerning the DOM composition obtained by those methods, moved research towards two more specialized analytical techniques in RAS that prioritize the DOM fraction content: i) the UV absorbance at 254 nm, which is sensitive to the presence of aromatic fractions of DOM; and ii) the excitation-emission matrices (EEMs) of fluorescence combined with parallel factor analysis (PARAFAC), which can identify different classes of fluorescent DOM (FDOM) The ability of the latter to characterize the fluorescence fraction of DOM, provides a more descriptive approach to monitor OM changes in RAS.
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