## 3 Results
### Onset of Nitrification  
The mean concentration of total ammonia nitrogen (TAN) varied over days (\(p<0.05\)) but not between treatments while the mean concentrations of nitrite (\(p<0.0001\)), nitrate (\(p<0.0001\)) and pH (\(p<0.0001\)) differed significantly between treatments and over days. The maximum TAN concentration in the aquaponic treatment (2.00 \(\pm\) 0.00 mg/L, \(n=3\)) was reached on day 6 and it gradually decreased to zero by day 11. In RAS the maximum TAN (2.67 \(\pm\) 0.58 mg/L, \(n=3\)) was reached on day 9, and it decreased to 0 by day 18 (Figure 1a). From day 18 the concentration of TAN stayed at nearly zero in both treatments until the end of the experiment. The mean nitrite concentration decreased close to zero in the aquaponics treatment on day 11 while it took 39 days in RAS treatment (Figure 1b). The highest mean nitrite concentrations were recorded (4.83 \(\pm\) 0.28 mg/L, \(n=3\)) in aquaponics on day 7 but on day 11 in RAS treatment (Figure 1b). During the experiment, the highest mean nitrate concentration was recorded on day 9 in aquaponics (81.67 \(\pm\) 2.88 mg/L, \(n=3\)) while on day 14 (80 mg/L) in RAS treatment (Figure 1c). The mean concentration of the nitrate followed a gradual decline and stayed lower in aquaponics compared to RAS treatment during the experiment until day 39 but became almost equal on day 42 (Figure 1c). The pH of the circulating water was significantly different between the treatments over the course of the experiment (\(p<0.0001\)), and it gradually decreased during the experiment. The mean daily pH in the RAS treatment varied between 7.79 \(\pm\) 0.00 (\(n=3\)) and 6.43 \(\pm\) 0.05 (\(n=3\)) while in aquaponics it varied between 7.76 \(\pm\) 0.05 (\(n=3\)) and 6.83 \(\pm\) 0.05 (\(n=3\)) (Figure 1d). \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & **Aquaponics** & \multicolumn{2}{c}{**Hydroponics**} & **Sig.** \\ \hline Fe (mg/kg) & 523.3 & \(\pm\)75.05 & 143.3 & \(\pm\)15.25 & * \\ Cu (mg/kg) & 37.30 & \(\pm\)12.70 & 49.30 & \(\pm\)9.60 & ns \\ Mn (mg/kg) & 403.3 & \(\pm\)40.41 & 366.6 & \(\pm\)246.84 & ns \\ Zn (mg/kg) & 526.6 & \(\pm\)142.9 & 206.6 & \(\pm\)55.07 & * \\ B (mg/kg) & 120.0 & \(\pm\)0.00 & 32.30 & \(\pm\)8.08 & * \\ N (g/kg) & 38.70 & \(\pm\)3.00 & 57.50 & \(\pm\)2.61 & * \\ P (g/kg) & 6.06 & \(\pm\)1.10 & 9.40 & \(\pm\)1.55 & * \\ K (g/kg) & 64.60 & \(\pm\)5.68 & 83.30 & \(\pm\)8.96 & * \\ Ca (g/kg) & 36.60 & \(\pm\)3.51 & 7.26 & \(\pm\)0.35 & * \\ Mg (g/kg) & 16.60 & \(\pm\)1.52 & 5.80 & \(\pm\)1.01 & * \\ S (g/kg) & 3.56 & \(\pm\)0.41 & 5.63 & \(\pm\)0.47 & * \\ \hline \hline \end{tabular} Values are means \(\pm\) SD from three replicated rafts (\(n=3\)). Statistical difference (Sig.) in the values between aquaponics and hydroponics treatments is shown by an asterisk * (\(p<0.05\)), ns = not significant.  
\end{table} 
Table 3: Micronutrients (mg/kg) Fe, Cu, Mn, Zn, B and macronutrients (g/kg) N, P, K, Ca, Mg, S in spinach (_Spinacia oleraca_) shoots grown in hydroponic and aquaponic system for 42 days. For aquaponics treatment spinach was grown in a coupled aquaponics system together with rainbow trout (_Oncorhynchus mykiss_). \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & **Hydroponics** & \multicolumn{2}{c}{**Aquaponics**} \\ \hline Shoot weight (g) & 0.88 & \(\pm\)0.27 & 1.23 & \(\pm\)0.34 \\ Root weight (g) & 0.18 & \(\pm\)0.08 & 0.30 & \(\pm\)0.16 \\ Total weight (g) & 1.07 & \(\pm\)0.29 & 1.53 & \(\pm\)0.48 \\ Shoot length (cm) & 12.15 & \(\pm\)1.32 & 14.50 & \(\pm\)1.69 \\ Root length (cm) & 29.23 & \(\pm\)4.63 & 37.77 & \(\pm\)5.73 \\ Shoot to root ratio weight & 5.54 & \(\pm\)2.77 & 4.50 & \(\pm\)1.46 \\ Shoot to root ratio length & 0.44 & \(\pm\)0.02 & 0.40 & \(\pm\)0.03 \\ \hline \hline \end{tabular} Values are means \(\pm\) SD of one plant at the end of the experiment from three replicated rafts, \(n=3\), average start weight for total weight = 0.003 \(\pm\) 0.0005. There were no statistically significant differences between the treatments.  
\end{table}