Spoilage Investigation of Chill Stored Meagre (Argyrosomus regius) Using Modern Microbiological and Analytical Techniques

Spoilage status of whole and filleted chill-stored meagre caught in January and July was evaluated using sensory, microbiological, 16S metabarcoding and Volatile Organic Compounds (VOCs) analysis. Based on the sensory analysis, shelf-life was 15 and 12 days for the whole fish taken in January and July, respectively, while 7 days for fish fillets of both months. For the whole fish, Total Viable Counts (TVC) at the beginning of storage was 2.90 and 4.73 log cfu/g for fish caught in January and July respectively, while it was found about 3 log cfu/g in fish fillets of both months. The 16S metabarcoding analysis showed different profiles between the two seasons throughout the storage. Pseudomonas (47%) and Psychrobacter (42.5%) dominated in whole meagre of January, while Pseudomonas (66.6%) and Shewanella (10.5%) dominated in fish of July, at the end of shelf-life. Regarding the fillets, Pseudomonas clearly dominated at the end of shelf-life for both months. The volatile profile of meagre was predominated by alcohols and carbonyl compounds. After univariate and multivariate testing, we observed one group of compounds (trimethylamine, 3-methylbutanoic acid, 3-methyl-1-butanol) positively correlating with time of storage and another group with a declining trend (such as heptanal and octanal). Furthermore, the volatile profile seemed to be affected by the fish culturing season. Our findings provide insights into the spoilage mechanism and give information that helps stakeholders to supply meagre products of a high-quality level in national and international commerce.

Phenotypic and Genetic Components for Growth, Morphology, and Flesh-Quality Traits of Meagre (Argyrosomus regius) Reared in Tank and Sea Cage

Meagre (Argyrosomus regius) plays an important role in the aquaculture system, with the potential for diversification of European aquaculture, and is characterized by its fast growth rate, low feed conversion ratio, and the high quality of the product. Focusing on the relevance of meagre, the aim of the study was to analyze growth performance, fish morphology, and flesh composition phenotypically and genetically to be considered as a strategy in a breeding program. For this purpose, 633 fish were raised in two different housing systems, in sea cages or in a continental tank, and when they reached harvest size, manual growth traits, automatic morphology by the image analysis program IMAFISH_ML, and flesh chemical composition (fat, protein, moisture, and collagen percentages) were measured. The fish reared in the cages showed a higher body weight and fillet fat percentage than those in the tank. Heritabilities for growth and morphology traits, and for fillet fat percentage were medium, revealing these traits as a possible selection criterion in a breeding program. Phenotypic and genetic correlations between growth and morphology traits were positive and high. Phenotypic correlations between growth or morphology traits with fillet fat percentage were positive and medium; genetic correlations were not estimated accurately.

Functional Feeds to Tackle Meagre (Argyrosomus regius) Stress: Physiological Responses under Acute Stressful Handling Conditions

Marine algae are recognised sources of bioactive compounds that have attracted great interest as nutritional supplements for aquaculture fish. Intensive rearing conditions often expose fish to husbandry-related stressors, rendering fish more susceptible to disease and reducing production yields. The present work evaluated the potential of two marine algae extracts (Fucus vesiculosus and Nannochloropsis gaditana) as nutritional supplements to mitigate stress effects in meagre (Argyrosomus regius) exposed to an acute handling stress (AS). A plant-based diet was used as a control, and three other diets were prepared, which were similar to the control diet but supplemented with 1% of each algal extract or a combination of the two extracts (0.5% each). The effects of supplemented diets on stress biomarkers, antioxidant enzyme activities, and immune response were analysed in fish exposed to AS after 4 weeks of feeding. Supplemented diets did not affect growth performance but the inclusion of F. vesiculosus promoted higher feed efficiency, as compared to the control group. Dietary algal extracts supplementation reduced plasma glucose levels, increased white blood cell counts, and reduced the expression of pro-inflammatory genes when compared with the control. N. gaditana supplementation led to a reduction in hepatic antioxidant enzyme activity and glutathione levels, while F. vesiculosus supplementation increased muscle glutathione reductase activity and reduced lipid peroxidation. These findings support the potential of algal extracts as nutraceuticals in aquafeeds to enhance the ability of fish to cope with husbandry-related stressful conditions and ultimately improve fish health and welfare.

Effect of Cold Smoking and Natural Antioxidants on Quality Traits, Safety and Shelf Life of Farmed Meagre (Argyrosomus regius) Fillets, as a Strategy to Diversify Aquaculture Products

Aquaculture has been playing a leading role over the years to satisfy the global growing demand for seafood. Moreover, innovative techniques are necessary to increase the competitiveness, sustainability and profitability of the seafood production chain, exploiting new species from the aquaculture, such as meagre (Argyrosomus regius), to develop value-added products and diversify their production. In the present work, the effectiveness of cold smoking combined with antioxidants (SA) compared to cold smoking alone (S) on meagre fillets, the quality and shelf life were investigated. Sensory, biochemical, physical–chemical and microbiological analyses were performed on the smoked fillets during vacuum-packaged storage for 35 days at 4 ± 0.5 °C. The results showed positive effects of the SA treatment on the biochemical parameters of meagre fillets. The total volatile basic nitrogen (TVB-N) in smoked meagre fillets was significantly lower in the SA treatment at the end of storage compared to the S treatment. Moreover, SA had a positive effect on lipid peroxidation. Lower values of malondialdehyde (mg MDA/kg) were observed in the SA treatment during preservation compared to the S treatment. This work will contribute to the growth of the fish production chain, producing a value-added fish product by exploiting meagre, whose production has been increasing over decades.

Dietary Phospholipids Enhance Growth Performance and Modulate Cold Tolerance in Meagre (Argyrosomus regius) Juveniles

Meagre (Argyrosomus regius) is a fast-growing species currently produced in aquaculture. This species is highly sensitive to low environmental temperatures which results in high mortality events during production cycles. In this study, the effects of dietary phospholipids (PLs) on growth and cold tolerance were evaluated. For this purpose, control (CTRL) and PL-enriched diets (three-fold higher levels than CTRL) were supplied to meagre juveniles (12.9 ± 2.5g) for 60 days, and growth was determined using a longitudinal approach. Weight gaining and SGR reduction were significantly different between dietary treatments. Animals fed with the PL-enriched diet were 4.1% heavier and grew 3.2% faster than those fed with the CTRL diet. Survival was higher than 98% in both groups. After finishing the growth trial, animals were submitted to two cold challenges and cold tolerance was evaluated as temperature at death (Tdeath), risk to death and lethal doses (LD) 50 and 90 using the cumulative degree cooling hours 6 h (CD6H). Tdeath ranged between 7.54 and 7.91 °C without statistical differences between dietary treatments. However, risk to death was significantly smaller (0.91-fold lower) and LD50 and LD90 were higher in animals fed with the PL-enriched than those supplied the CTRL diet. To assess the fatty acid (FA) composition of liver and brain in animals fed both diets after a cold challenge, FA profiles were determined in juveniles maintained at 14 °C and challenged at 7 °C. FA amounts increased in the liver of animals challenged at 7 °C. In contrast, several FAs reduced their levels in the PL-enriched diet with respect to CTRL indicating that these animals were able to mobilize efficiently lipids from this organ mitigating the negative effects of lipid accumulation during the cold challenge. In brain, the PL-enriched diet increased DHA level during the cold shock indicating a role in maintaining of brain functions. These results open a new research line that could improve the cold tolerance of meagre through dietary supplementation before winter.