###### Abstract  
The aim of the study was to evaluate the growth, fatty acid profile and concentration of malondialdehydedehyde of muscle tissue of meagre _Argyrosomus regius_ fed diets with different lipid content. The long-term experiment was conducted in three feeding groups: A (CP = 52.0; CL = 21.0), B (CP = 56.0; CL = 18.0), C (CP = 48.0; CL = 16.0) with two replicates in marine net cages on Bisage Island, Adriatic Sea over 20 months. At the beginning of the experiment, fish were of equal weight (6.83 \(\pm\) 1.03 g) and length (8.57 \(\pm\) 0.49 cm) and were fed to satiation during the experiment. At the end of the experiment, the fish from each feeding group (n = 110) were measured and muscle tissue was collected (\(n\) = 60) and stored at \(-\)80 \({}^{\circ}\)C until analysis. The final weight and condition factor were significantly different (\(p\) < 0.05) between the groups. The highest ratio of crude fats and n-3/n-6-fatty acids was found in the muscle tissue of group A. Fish fed diet A also exhibited higher MDA levels compared to fish in the other feeding groups, indicating elevated levels of lipid peroxidation in muscle tissues. Experimental feeding group A showed better growth performance, a higher content of the beneficial fatty acids EPA and DHA and a more favorable n-3/n-6 ratio than feeding groups B and C. Continuously monitoring and adjusting feeding protocols in accordance with lipid content and fatty acid composition could maximize growth and health outcomes in meagre farming. a 2024  
nutritional value [6; 10]. In addition, it has a high meat quality and is suitable for industrial processing [11; 12] which emphasizes meagre as a highly marketable species. Due to the highlighted characteristics, meagre has also become an increasingly important fish species due to the need for species diversification in Mediterranean maritime [13; 14]. Fish nutrition is one of the most demanding technological processes and plays a direct key role in intensive aquaculture as it affects the production cost, growth and health of the rearing organism [15]. There is a close relationship between the quality of fish feed (or pollution load) and the nutritional value of the species, i.e., protein content, phospholipid composition and the proportion of unsaturated fatty acids, especially DHA and EPA [16]. Dietary lipids are not only an important source of energy, but also a source of fatty acids needed for the synthesis of new cell lipids for growth and reproduction and for the turnover of existing lipids [17]. The type and amount of dietary lipids can influence fish metabolism, immune function, and the fatty acid composition of tissues [18]. Determining the basic nutrient requirements of a species, especially the optimal ratio between proteins and lipids, along with the inclusion of optimal amounts of fish oil, is essential for a balanced diet [7; 19]. A current trend in fish feeding is the use of higher proportions of lipids in the diet. While increasing the lipid content in the diet can help reduce high feed costs by partially saving protein in the feed, problems such as excessive fat deposits in the liver can affect fish health, quality and shelf life of the final product [20]. Marine fish oil is the richest available source of long-chain polyunsaturated fatty acids (PUFAs), which are important in human nutrition for a variety of important functions [21; 22]. However, the Marine Ingredients Organisation (IFFO) estimates that about 75% of annual fish oil production still goes into aquaculture feeds [23]. The fatty acid composition of individual fish oils varies considerably and is influenced by factors such as age, size, species, reproductive status, geographic location, and the season in which they are harvested. The major fatty acids found in the highest concentrations in fish oil include 14:0, 16:0, 16:1n-7, 18:1n-9, 20:5n-3 and 22:6n-3 [24].