# Mediterranean Aquaponics: Fasting and Refeeding in a Polyculture Aquaponic System
## 4 Discussion  
### Water Quality  
Throughout the experimental process, the levels of water quality indicators such as total alkalinity (TAN) and nitrate (NO\({}_{2}\)\({}^{-}\)) were maintained at minimal levels. Significant differences were observed between the treatments (ANOVA, \(p<\)0.05). The mean nitrate \begin{table}
\begin{tabular}{l c c c} \hline  & **A** & **B** & **C** \\ \hline Initial biomass (IB), g & 5.11 \(\pm\) 0.49 \({}^{\text{a}}\) & 5.09 \(\pm\) 0.53 \({}^{\text{a}}\) & 5.11 \(\pm\) 1.14 \({}^{\text{a}}\) \\ Initial height (IH), cm & 16.34 \(\pm\) 1.39 \({}^{\text{a}}\) & 16.73 \(\pm\) 1.24 \({}^{\text{a}}\) & 16.73 \(\pm\) 1.49 \({}^{\text{a}}\) \\ Initial branches (IBr) & 2.88 \(\pm\) 0.35 \({}^{\text{a}}\) & 3.00 \(\pm\) 0.66 \({}^{\text{a}}\) & 2.25 \(\pm\) 0.27 \({}^{\text{a}}\) \\ Final biomass (FB), g & 9.35 \(\pm\) 0.99 \({}^{\text{a}}\) & 11.63 \(\pm\) 1.47 \({}^{\text{a}}\) & 10.60 \(\pm\) 1.75 \({}^{\text{a}}\) \\ Final height (FH), cm & 23.43 \(\pm\) 0.91 \({}^{\text{a}}\) & 27.48 \(\pm\) 1.89 \({}^{\text{b}}\) & 20.48 \(\pm\) 1.77 \({}^{\text{a}}\) \\ Final branches (FBr) & 5.33 \(\pm\) 0.21 \({}^{\text{a}}\) & 6.33 \(\pm\) 0.67 \({}^{\text{a}}\) & 6.00 \(\pm\) 0.46 \({}^{\text{a}}\) \\ Yield (kg/m\({}^{2}\)) & 31.82 \(\pm\) 3.82 \({}^{\text{a}}\) & 42.38 \(\pm\) 5.66 \({}^{\text{b}}\) & 32.35 \(\pm\) 6.73 \({}^{\text{a}}\) \\ \hline \multicolumn{4}{c}{Photosynthetic pigments} \\ \hline Chlorophyll A (Ch1 a), mg/g & 15.20 \(\pm\) 0.88 \({}^{\text{ab}}\) & 13.99 \(\pm\) 0.84 \({}^{\text{a}}\) & 18.33 \(\pm\) 1.05 \({}^{\text{b}}\) \\ Chlorophyll B (Ch1 b), mg/g & 4.78 \(\pm\) 0.31 \({}^{\text{a}}\) & 4.62 \(\pm\) 0.38 \({}^{\text{a}}\) & 5.41 \(\pm\) 0.44 \({}^{\text{a}}\) \\ Carotenoids, mg/g & 5.03 \(\pm\) 0.29 \({}^{\text{a}}\) & 5.09 \(\pm\) 0.37 \({}^{\text{a}}\) & 5.53 \(\pm\) 0.21 \({}^{\text{a}}\) \\ \hline \multicolumn{4}{c}{Chemical composition} \\ \hline Nitrogen (\%) & 16.24 \(\pm\) 0.13 \({}^{\text{a}}\) & 17.75 \(\pm\) 0.25 \({}^{\text{b}}\) & 16.65 \(\pm\) 0.27 \({}^{\text{a}}\) \\ Ash (\%) & 13.55 \(\pm\) 0.15 \({}^{\text{a}}\) & 13.59 \(\pm\) 0.29 \({}^{\text{a}}\) & 14.64 \(\pm\) 0.15 \({}^{\text{b}}\) \\ Moisture (\%) & 79.31 \(\pm\) 1.85 \({}^{\text{a}}\) & 85.59 \(\pm\) 1.52 \({}^{\text{b}}\) & 86.75 \(\pm\) 0.72 \({}^{\text{b}}\) \\ \hline \end{tabular} Data are expressed as mean \(\pm\) SEM (N = 24). Means in a row followed by the same superscript are not significantly different (ANOVA, \(p>\) 0.05).  
\end{table} 
Table 4: Glasswort growth performance, photosynthetic pigments, and content at the end of the cultivation period (75 days). Figure 6: Changes in compensation coefficient of European sea bass juveniles fed according to different feeding frequencies for 75 days. values at the control site, situated at the outlet of the hydroponic subsystem (NO3\({}^{-}\)out), were found to be lower than those at the control site within the fish tank (NO3\({}^{-}\)in). This indicates that the plants were absorbing nutrients from the water. However, the water quality parameters remained within the optimal limits for both the aquaculture [34] and hydroponic systems [1]. This study demonstrated that compensatory growth can effectively reduce ammonia levels [35]. The increased nitrate ions were utilized by the plants for nutritional and growth purposes [1]. Ammonia serves as a suitable source of nutrients for plants, particularly when nitrate levels are low. However, plants absorb significantly more nitrate when ammonia levels increase [36]. [PERSON] and [PERSON] [37] observed that in an aquaponic system with fresh water, where lettuce was cultivated, the retention efficiency of ammonia (NH4\({}^{+}\)/NH3) was superior to that of nitrate ions. In the present study, ammonia levels were maintained at a consistently low level throughout the experimental period, with the maximum value occurring in treatment B. This suggests that ammonia was oxidized to nitrite and nitrate ions more effectively in treatment C, which supports the uptake and growth of glasswort plants. Ref.