## 2 Materials and Methods
### Sample Preparation and Analysis  
During the experiment, there were around 9000 fish in each cage. For the basic morphometric analysis, 100-110 specimens were sampled from each cage to measure total length (TL, cm) and wet weight (W, g). Before measurement, the fish were anesthetized with 0.2 g/L tricaine methanesulfonate (MS-222, Sandoz, Switzerland). The biometric measurements were performed monthly, and after the measurement the fish were returned to the cage. At the end of the study, samples were taken for the fatty acid profile. The [PERSON]'s condition factor (K) was calculated on the basis of the measurements:  
\[\text{K}=\text{W}/\text{TL}^{3}\times 100.\]  
The biomass in the cages was estimated from the weight measurements and the total number of fish per cage at the beginning and the end of the experiment. The fish were fed twice daily from May to December until obvious satiation, and once daily during the remaining months. Feed intake was recorded daily for each cage. Growth and nutrient utilization indices were calculated based on the collected data:  
Specific growth rate (SGR) = ln (final weight \(-\) initial weight)/duration of the experiment (days),  
Thermal growth coefficient (TGC) = final weight \(1/3-\) initial weight \(1/3/\)(t \(\times\) duration of the experiment (days)) \(\times\) 1000,  
Feed conversion ratio (FCR) = feed offered (g)/weight gain (g). Twenty samples were collected from each experimental group (A, B, C) (10 from each experimental unit, N = 60). Fish were stored at \(-\)80 \({}^{\circ}\)C before further processing. Samples were dissected and 10 g of muscle was separated from the remaining tissue and homogenized in a blender to determine the composition of malondialdehydehehyde, lipids and fatty acids. The total MDA concentration in 10% of the homogenates in 0.14 M potassium chloride was measured by high-performance liquid chromatography (HPLC) according to \begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**Feed Mixtures**} \\ \hline
**Proximal Composition (\% of Diet)** & **A** & **B** & **C** \\ \hline Crude protein & 52.0 & 56.0 & 48.0 \\ Crude fat & 21.0 & 18.0 & 16.0 \\ Crude fiber & 0.7 & 0.4 & 3.0 \\ Ash & 11.4 & 10.4 & 8.3 \\ P & 1.6 & 1.65 & 1.12 \\ Ca & 2.4 & 2.11 & 1.87 \\ Na & 0.9 & 0.68 & 0.38 \\ _Vitamins (UIL/kg)_* & & & \\ \hline Vit. A & 15,000 & 15,000 & 15,000 \\ Vit D\({}_{3}\) & 2500 & 800 & 800 \\ Vit C & 500 & 150 & 200 \\ Vit E & 300 & 150 & 250 \\ _Microelements (mg/kg)_ & & & \\ \hline Cu & 4.7 & 1.5 & 4.1 \\ Mn & - & 12 & 12 \\ Na (ug/kg) & 438 & - & - \\ Zn & 301 & 75 & 75 \\ I & 4.6 & 1.8 & 1.8 \\ _Antioxidants (mg/kg)_ & & & \\ \hline Propyl galate & 22 & 100 & 100 \\ BHA * & - & 100 & 100 \\ Citric acid & 20 & - & - \\ \hline \hline \end{tabular}  
* UI—international unit code,  
\end{table} 
Table 1: Proximal composition of experimental feed (A); commercial feed for sole (B); commercial feed for meagre (C). the modified method of [35]. RP HPLC analysis was performed on the TSP \(-\)130 system (Thermo Separation Products, Inc, Thermo Fisher Scientific, Inc, Waltham, MA, USA) using the Waters symmetry(r) C18 column (Waters, Milford, MA, USA) with a length of 25 cm, a radius of 4.6 mm, and a particle size of 5 \(\upmu\)m. The mobile phase consisted of methanol and 50 mM potassium dihydrogen phosphate in a 50:50 ratio. The flow rate of the mobile phase was 1 mL/min, the analysis time was 10 min, and the wavelength of the UV detector was 532 nm. Under these conditions, the retention time is 3 min. The linearity of this method was 0.99 and the reliability was 99%. Total lipids (TL) of homogenized muscle were extracted according to the method of [36]. The extract layers were separated at least three times with the addition of a salt solution to maximize lipid recovery, and the organic phases were combined and evaporated to dryness. The total lipid content was weighed after evaporation of the solvent.