## 4 Discussion  
The results of this study demonstrate that stocking density has a significant effect on several parameters of growth, feed efficiency, and physiological response in _D. latforms_, as well as on the growth of chard plants in a small-scale, low-technology aquaponic system. The fish cultured in this work achieved growth rates higher than those reported by [PERSON] et al. [19] with the same species (_D. latforms_) and comparable to those obtained by [PERSON] et al. [13] in plastic ponds in a recirculation system. However, [PERSON] et al. [20] reported higher growths than those obtained in the present investigation in concrete ponds without recirculation. Furthermore, in the daily growth rate (DWG) analysis, the highest stocking density treatment (T3, 50 fish m\({}^{-3}\)) showed the lowest average (0.48 \(\pm\) 0.08 g fish\({}^{-1}\) day\({}^{-1}\)) (Table 2). This result is consistent with previous studies that have shown that high stocking densities can limit fish growth, mainly due to competition for space and resources [21; 22; 23; 24]. Unequal growth of fish with increasing stocking density has been reported in aquaponic systems [25; 26; 27; 28; 29]. The difference in growth of _D. latforms_, which was presented in this work in the different treatments, may be due to stress from overcrowding (competition for space) which probably triggered an increase in energy demand to cope with the stress causing a reduction in the energy available for growth [21; 22; 25]. Similarly, the FCR in this study showed significant differences among treatments, with more favorable values in the lowest stocking density treatment (T1, 10 fish m\({}^{-3}\)) (Table 2). This finding suggests that fish cultured at low stocking densities utilize feed more efficiently, possibly due to lower stress derived from less competition for feed and better water quality [22; 30; 31]. On the other hand, net yield (NY) was significantly higher in the T3 treatment (3329 \(\pm\) 151 g m\({}^{-3}\)), indicating that, despite lower individual growth, total biomass production was higher at high stocking densities. Although no significant differences in survival were observed, a negative trend was detected as culture density increased (100% at T1, 94% \begin{table}
\begin{tabular}{c c c c} \hline
**PARAMETERS** & **T1 (10 org m\({}^{-3}\))** & **T2 (30 org m\({}^{-3}\))** & **T3 (50 org m\({}^{-3}\))** \\ \hline hct (hematocrit) (\%) & 35.4 \(\pm\) 6.0 & 37.3 \(\pm\) 4.8 & 33 \(\pm\) 5.2 \\ Glucose (mg dL\({}^{-1}\)) & 69.9 \(\pm\) 12.9 a  & 27.7 \(\pm\) 7.2 b  & 70.6 \(\pm\) 23.3 a  \\ Total protein (g dL\({}^{-1}\)) & 3.8 \(\pm\) 0.7 & 3.2 \(\pm\) 0.8 & 3.2 \(\pm\) 0.5 \\ Albumin (g dL\({}^{-1}\)) & 1.5 \(\pm\) 0.2 & 1.7 \(\pm\) 0.3 & 1.7 \(\pm\) 0.2 \\ Globulins (g dL\({}^{-1}\)) & 2.2 \(\pm\) 0.7 a  & 1.6 \(\pm\) 0.4 ab  & 1.4 \(\pm\) 0.6 b  \\ A/G & 0.8 \(\pm\) 0.2 a  & 1.4 \(\pm\) 0.5 b  & 1.1 \(\pm\) 0.2 b  \\ Triglycerides (g dL\({}^{-1}\)) & 404.4 \(\pm\) 12.9 a  & 401.9 \(\pm\) 34.5 a  & 250.8 \(\pm\) 36.6 b  \\ Cholesterol (g dL\({}^{-1}\)) & 128.6 \(\pm\) 29.8 & 138.8 \(\pm\) 27.3 & 128.6 \(\pm\) 29.8 \\ Cortisol (ng ml\({}^{-1}\)) & 51.9 \(\pm\) 20.2 & 64.5 \(\pm\) 14.7 & 71.9 \(\pm\) 35.4 \\ Chlorine (mEd L\({}^{-1}\)) & 111 \(\pm\) 18.2 & 112.4 \(\pm\) 12.9 & 114.0 \(\pm\) 3.9 \\ Calcium (mg dL\({}^{-1}\)) & 6.8 \(\pm\) 0.9 & 7.4 \(\pm\) 1.6 & 8.2 \(\pm\) 2.2 \\ \hline \end{tabular}
\end{table} 
Table 3: Blood parameters evaluated after 157 days of experimentation of _Dormitator latforms_ in a small-scale aquaponic culture with _Beta vulgaris_. Treatments with different superscripts represent significant differences (\(p<0.05\)). at T2, and 91% at T3), which could be related to higher stress caused by the factors mentioned above. Some authors [20] obtained higher survival intervals (99-100%) in one crop at different stocking densities with the same species. However, this may be because they used 3, 5, 6, and 7 org m\({}^{-3}\) and in the present study the lowest stocking density implemented was 10 org/m\({}^{3}\).