Short communication Copper bioavailability and impact on bacterial growth in flow-through rainbow trout aquaculture systems Andreas Tom-Petersen, Kristian K. Brandt, Ole Nybroe, Niels O.G. Jørgensen ⁎ Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark abstract article info Article history: Received 11 May 2011 Received in revised form 25 September 2011 Accepted 27 September 2011 Available online 2 October 2011 Keywords: Trout breeding Copper bioavailability Biosensor Microbial community impact Copper is an important additive in the aquaculture industry for control of algal growth and ecto-parasites. However, copper may impact microbial communities depending on its biological availability and hence neg- atively affect microbial degradation of organic matter or other microbial ecosystem services. Here we applied a whole-cell bacterial biosensor to determine copper bioavailability (proportion of bioavailable vs. total cop- per) in water from three rainbow trout aquaculture facilities. Copper bioavailability varied between 24 and 37% and the differences were compatible with differences in carbonate alkalinity, concentration of dissolved organic matter and amounts of suspended matter in the water. Subsequently, we determined the effect of copper on bacterial growth activity at concentrations realistic for aquacultures. Although a field exposure to ca. 0.1 μM bioavailable Cu had no effect, laboratory exposure to comparable concentrations reduced the bacterial growth activity. Hence, common copper amendment procedures may lead to concentrations close to the threshold that impacts bacterial activity. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Copper salts are commonly used algaecides and agents for removal of ecto-parasites in the aquaculture industry (Noga, 2000; Schlenk et al., 1998). Similarly, these copper compounds are utilized to control macroalgae and bivalve growth in shrimp farming (Frìas-Espericueta et al., 2008; Lyle-Fritch et al., 2006). Copper (Cu) at levels typically ap- plied to fish ponds is generally not toxic to fish. In aquaculture systems, however, Cu may affect microbial degradation of organic matter, since Cu at even low concentrations (below 0.1 μM) has been shown to re- duce bacterial growth activity in aquatic systems (Boyd et al., 2005). This means that application of Cu to improve fish health may lower the degradation of organic matter in both ponds and sludge de- posits. In addition, Cu and other toxic metals can select for resistance to antibiotic compounds (Baker-Austin et al., 2006; Berg et al., 2010; Stepanauskas et al., 2005). Impacts of Cu on living organisms are traditionally related to total dissolved Cu concentrations as determined by chemical procedures (Niyogi and Wood, 2004). However, the bioavailability and toxicity of Cu depend on water characteristics such as pH, alkalinity and con- centrations of dissolved and particulate organic matter (Boyd et al., 2005; Brooks et al., 2008) and changes in one or more of these param- eters may alter bioavailability and toxicity of Cu. This knowledge has led to the development of the biotic ligand model (BLM) that integrates the concepts of metal bioavailability, assumed to depend on the free metal ion activity and competition for biotic binding sites with other cations, and equilibrium-based metal speciation for prediction of aquatic Cu toxicity (Niyogi and Wood, 2004). Although the BLM has advanced our ability to predict metal toxicity the model does not always success- fully predict Cu toxicity as exemplified in a recent study with rainbow trouts in softwater systems (Ng et al., 2010). Rather than estimating the bioavailable fraction of Cu by chemical speciation modeling, it is also possible to directly measure Cu bioavail- ability by biosensor technology. A bioluminescent, whole-cell bacterial biosensor that responds specifically to bioavailable Cu species by emit- ting light (Brandt et al., 2008; Tom-Petersen et al., 2001), represents an advantageous complement to chemical assays for total Cu determina- tion. Indeed, it has been demonstrated that some Cu-dissolved organic matter complexes contribute to Cu bioavailability (Nybroe et al., 2008) and biosensor data has recently been shown to correlate better to Cu impacts in diverse bacterial communities than other Cu exposure descriptors (Brandt et al., 2010). Hence, biosensor methodology may at least in some cases confer distinct advantages over chemical methods for measurement of Cu bioavailability whereas chemical speciation- based modeling confers a powerful approach for prediction of metal toxicity to bacteria in environments with similar and stable pools of dis- solved organic matter (Ore et al., 2010). The current study had two aims: First, we compared Cu bioavail- ability in soft and fresh water from three flow-through rainbow trout aquaculture facilities in Denmark using a whole-cell biosensor approach. Second, we determined the impact on bacterial growth activity of Cu concentrations realistic for aquaculture systems using Aquaculture 322-323 (2011) 259–262 ⁎ Corresponding author. Tel.: + 45 35332625; fax: + 45 35332606. E-mail address: nogj@life.ku.dk (N.O.G. Jørgensen). 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.09.038 Contents lists available at SciVerse ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online