The aim of the study was to evaluate the growth, fatty acid profile and concentration of malondialdehyde 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 ± 1.03 g) and length (8.57 ± 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 °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.

Parasitic diseases pose significant challenges to the success of mariculture. The health management strategies used in sea-cage aquaculture are not completely effective at preventing parasites from entering through interactions with wild fish. This study monitored the health status of greater amberjack (Seriola dumerili, Risso 1810) over a two-month period following their introduction to the farm in the Middle Eastern Adriatic Sea in July 2019. Zeuxapta seriolae was detected on the gills after 722 degree days (DD), with a 28% prevalence, a mean abundance of 1.00 parasite per fish (four examined arches), and a mean intensity of 3.57 parasites per infected fish. From 985 DD, prevalence was 100%; the parasite burden continued to rise, and by the final sampling at 1535 DD, the mean abundance reached 212.68 parasites per fish (53.17 per gill arch). At that point, fish express a sudden loss of appetite; no external symptoms were observed, except for mortality. This is the first report of Z. seriolae in cultured greater amberjack in the Adriatic Sea, and the study emphasises the difficulties in applying effective biosecurity measures in floating net cages.

The gilthead seabream (Sparus aurata) is cultured throughout the Mediterranean; the sea temperature most significantly determines the duration of farming. Sea temperatures reduce gilthead seabream’s need for feed and fish growth is not expected in these conditions. It is hypothesized that improving feed formulation could improve growth during the winter months. For the research, two groups were formed, and fed for a month with two types of fish feed of different nutritional composition at an average temperature of 13.9 ± 0.90 °C. The fish from cage A (21.53 ± 1.53 cm; 173.77 ± 38.24 g) were fed fish feed containing protein and lipid 100% from marine origin (H1). The fish from cage B (22.17 ± 1.43 cm; 181.08 ± 43.05 g) were fed with commercial feed for gilthead seabream, whose proteins and lipids were partially replaced by plant raw materials (H2). The temperature was measured daily and samples were taken at the beginning and end of the experiment for biometrics, which included the fish’s total length, total weight, and condition factor. This study showed that fish fed with a modified formula achieved higher growth parameters than fish fed with commercial feed. The data obtained indicate that gilthead seabream can grow at low temperatures and there is a need for further research to ensure the correct selection of raw materials for the testing and production of feed for the period of low sea temperatures.

Low seawater temperatures are expected to depress fish growth in aquaculture. However, recent evidence suggests diet composition may offer mitigation for some species. This study evaluated the impact of different diets on juvenile meagre (Argyrosomus regius) in cage farming at low seawater temperatures (average 15.19 °C), conditions known to typically suppress meagre growth. Three replicated groups of fish (initial weight ≈ 107 g) were fed for six months either sardines (group A) or commercial pellets (groups B/C, with group C moisturized). The results demonstrate that the nutritional profile of sardines effectively mitigates cold-induced growth reduction in meagre. While pellet-fed meagre experienced expected growth depression, sardine-fed meagre exhibited a doubled temperature growth coefficient (TGC) and an 80% higher final average weight than the pellet groups (A: 346.13 g, B: 194.44 g, C: 188.93 g).

This study presents, for the first time, the occurrence and community structure of wild fish inside marine aquaculture cages of gilthead seabream (Sparus aurata), European sea bass (Dicentrarchus labrax), greater amberjack (Seriola dumerili), meagre (Argyrosomus regius), and common dentex (Dentex dentex). Coexistence of farmed and wild fish was observed only in cages of gilthead seabream and European sea bass, with wild fish constituting 0.08% of the total sampled fish biomass. Twelve wild fish species from five families were recorded: Carangidae, Clupeidae, Mugilidae, Moronidae, and Sparidae. Bogue (Boops boops) and jack mackerel (Trachurus sp.) were the most abundant. Multivariate analysis indicated that location significantly influenced the wild fish community composition, while reared species and farming duration, along with their interaction, had no significant effect. Descriptive comparisons suggested potential differences in biometric traits of bogue and jack mackerel between reared species and farming duration. The findings highlight the need for further research on wild fish in cages to better understand the potential health and biosecurity risks they may pose.