Effect of Soluble CO2 Stabilization on the Quality of Fillets from Farmed Gilthead Sea Bream (Sparus aurata) and European Sea Bass (Dicentrarchus labrax)

ABSTRACT

Soluble gas stabilization (SGS) is a relatively recent methodology of active packaging that has been proposed to extend the shelf life of packaged fish. The aim of the present work was to study the effect of SGS applied at different extents (2 bars: 30 and 60 min) on the shelf life of sea bream and sea bass fillets packed in air during chilled storage. Quality changes were evaluated by sensory assessment, microbiological analysis (TVC), TBARs, pH value, TVB-N, and TMA-N. No significant extension of sensory shelf life was visible as a function of SGS treatment. The treatment of fillets in CO₂ at 2 bars during 60 min had a positive effect on the microbiological shelf life of both species. On the other hand, TMA-N and TVB-N showed similar changes during storage period and were not affected by the CO₂ treatment. Sea bream treated with SGS always presented higher TBARs than control samples. Nevertheless, oxidation of sea bream and in particular, of sea bass fillets, did not appear to be a significant problem during chilled storage.     

Influence of dietary levels of soybean meal on the performance and gut histology of gilthead sea bream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax L.)

The present study was performed to determine the effect of soybean meal (SBM) on the performance and gut histology of gilthead sea bream and European sea bass. Three isonitrogenous and isolipidic extruded diets (crude protein, 470 g kg⁻¹ diet; crude fat, 200 g kg⁻¹ diet) were formulated containing 0 (0 SBM), 180 (180 SBM) and 300 (300 SBM) g kg⁻¹ diet SBM and tested on both species in two separate experiments. Fish at an initial average weight of around 18 g were randomly allocated to 800 L square tanks connected to a closed recirculating system. The trials lasted 80 days for sea bream and 89 days for sea bass. Fish were hand-fed to apparent satiation. Increasing the level of SBM had no significant effects on the specific growth rate, feed intake and feed conversion rate in both the species. In the sea bream distal intestine, lamina propria was moderately and diffusely expanded in some fish due to an increase in cell infiltration represented by mononuclear cells, this finding being more frequent in animals fed diet 300 SBM. No other morphological alterations in intestinal folds, enterocytes or other inflammation signs were noticed in the sea bream distal intestine of any group. No histological differences were found in sea bass in any experimental group.     

Annual cycle of plasma insulin and glucose of sea bass.Dicentrarchus labrax,L.

Annual plasma insulin and glucose cycles were studied inDicentrarchus labrax maintained in either seawater (37.8) or brackish water (3.5). In both media, the highest insulin levels were found during the prespawning period (August–November) coincident to increases in weight and a decrease in plasma glucose. During spawning (December–April) and postspawning (May–July) periods, the decrease in insulin occurred at the same time as a reduction in growth and an increase of plasma glucose. Temperature and salinity conditions impeded spawning in the brackish water group, in which a minor weight loss was regained more quickly than in the sea water group; insulin levels were also higher.     

Antibody response in sea bass (Dicentrarchus labrax L.) in relation to water temperature and oxygenation

The influence of water temperature and water oxygenation on the specific antibody response was evaluated by indirect ELISA in sea bass (Dicentrarchus labrax L.) immunized against human‐γ‐ globulins emulsified in Freund's complete adjuvant. A higher antibody response was observed in fish reared at 24 and 30 °C, than at 12 and 18 °C. For the fish group reared at 24 °C, the immunological observation was carried out until 300 days after immunization. At the end of this period, fish kept at 24 °C still showed immunological competence, although the antibody response began to decrease significantly from 120 days after the immunization. Fish reared under mild hyperoxia and normoxia conditions had higher antibody responses than fish reared under mild hypoxia conditions. Moreover, at the end of the experimental period of 56 days the antibody response of fish reared under hyperoxia conditions was significantly higher than the immune response detected in fish reared under normoxia and hypoxia conditions.     

Influence of tank volume on vitellogenesis and spawning performances in sea bass Dicentrarchus labrax L.

Sea bass, Dicentrarchus labrax (mean weight: 748±13 g), were maintained before and during vitellogenesis in 1, 3, 8, 16 and 32 m³ tanks, and then they were transferred to 2 m³ tanks, for the spawning season. During the first 2 months of the experiment, the growth rates were significantly lower in smaller tanks (1 m³). In August, the oocyte diameters were significantly lower in smaller tanks (1, 3 and 8 m³) than in larger (16–32 m³) tanks. At the end of the experiment, the fish mean weight in the 1 m³ tanks was significantly lower than in the 3 m³ tanks, but oocyte diameters and plasma oestradiol concentrations were not significantly different between the volumes. This shows a longer acclimation requirement in smaller volume rearing. Although all the females had not spawned, one spawn at least was collected in each volume. The variation in conditioning volume has not blocked the spawning process. The qualitative and quantitative characteristics of spawns were not significantly different between volumes. The conditioning volume of 3 m³ seems to be a minimal volume required to obtain good reproduction of sea bass.     

Evaluation of electrical stunning of sea bass (Dicentrarchus labrax) in seawater and killing by chilling: welfare aspects, product quality and possibilities for implementation

The objective was to assess neural, behavioural responses and product quality in farmed sea bass (Dicentrarchus labrax) upon electrical stunning in seawater. The electrical sinusoidal 50 Hz or pulse square wave alternating 133 Hz current induced a general epileptiform insult with a current of 3.3±0.2 or 3 A dm^?2, respectively, for 1 s head to tail in seawater. The total duration of the insult was 48±34 and 23±11 s. After stunning, the electro‐cardiogram revealed fibrillation and ceased or showed malfunction. Product quality was assessed in a group electrically stunned, followed by chilling in ice water and the controls were only chilled in ice water. The pH of the fillets was 0.1–0.2 lower (P<0.01) when stunned electrically at days 1, 2, 8 and 10 postmortem, where the colour did not differ. The percentage of sea bass effectively stunned using an electrical sinusoidal or pulse square wave current was above 85% within a confidence level of 95%. A combination of electrical stunning for 10 s, followed by chilling in seawater with ice flakes resulted in the death of all fish. The former method is recommended to be adapted for implementation in practice.     

Apparent digestibility coefficients of feed ingredients and their predictability in compound diets for gilthead seabream, Sparus aurata L.

Apparent digestibility of crude protein, amino acids, lipid, carbohydrate and energy was measured for a range of feed ingredients fed to gilthead seabream, Sparus aurata L. — fish meal, poultry meal, meat meal, blood meal, squid meal, extracted soyabean and wheat flour. Chromic oxide was used as a non-absorbed reference substance and faeces were collected by stripping. Diets compounded from mixtures of these ingredients were then used to examine the possibility of predicting the digestibility of formulated diets.
Apparent digestibility of crude protein ranged from 79% to 90%, lipids from 83% to 95% and energy from 72% to 88% in the different ingredients. Apparent digestibility of carbohydrates was lower and ranged from 49% to 77%. Apparent digestibility of amino acids was higher than that of crude protein and differences were found among digestibilities of individual amino acids.
Tests conducted using five compound diets indicated that ingredient digestibility was additive for protein, amino acids, lipids and energy, whereas the digestibility of carbohydrates in the compound feeds was slightly lower than predicted.
Diets for Sparus aurata may thus be formulated on the basis of digestibility of individual ingredients.     

Effect of electrical stunning at slaughter on the carcass, flesh and eating quality of farmed sea bass (Dicentrarchus labrax)

Food quality aspects of farmed sea bass (Dicentrarchus labrax) were compared following two methods of slaughter: the normal commercial method of killing, by immersion in an ice slurry, or by first electrically stunning the fish, before immersion in an ice slurry. Quality was assessed for up to 10 days of storage on ice after slaughter. No differences were found between the slaughter methods in terms of an overall sensory evaluation of cooked fillets, or in terms of overall carcass quality: overall appearance, internal and external haemorrhage, fin damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. Using objective measurements of colour, no differences between fish from either treatment were found in terms of external colour or colour of the fillets. A chemical analysis of flesh nucleotide breakdown products as well as the freshness indicator K_i value did not differentiate the two treatments nor did the industry standard freshness scoring technique (QIM, quality index method), over 10 days of storage on ice. Flesh pH was marginally lower in electrically stunned fish at 4 h post mortem (6.42 cf 6.56) but by 24 h, pH in fish from both treatments had decreased to a similar level (6.22). Humane electrical stunning of sea bass at slaughter neither measurably improved nor decreased product quality for between 1 and 10 days of storage on ice. Electrical stunning accelerated the pattern of onset and resolution of rigor mortis. If electrical stunning were to be widely adopted, re‐education of buyers would be necessary as rigor mortis is currently used by buyers as a proxy measure of fish freshness.     

Temperature-dependent pharmacokinetics and tissue distribution of oxolinic acid in sea bass, Dicentrarchus labrax L., after a single intravascular injection

The pharmacokinetics and tissue distribution of oxolinic acid following an intravascular administration (15 mg kg^?1 fish) were determined in sea bass, Dicentrarchus labrax L. (110 g), at 13 °C and 22 °C water temperature. The kinetic profile of the drug was found to be temperature dependent, with increased temperature having a greater effect on distribution after equilibrium and the elimination phase than on the distribution process. The distibution half‐life of oxolinic acid was 1.15 and 2.76 h at 22 °C and 13 °C respectively, whereas the elimination half‐life of the drug was 55 h at 22 °C and 315 h at 13 °C. The values of the apparent volume of distribution (1.44 L kg^?1 at 22 °C and 3.31 L kg^?1 at 13 °C) and the volume of distribution at steady state (5.2 and 14.7 L kg^?1 at the high and low temperature respectively) were considerably different between the two tested temperatures. The total body clearance of the antibiotic was found to be low (1.47 L kg^?1 day^?1 at 22 °C and 0.80 L kg^?1 day^?1 at 13 °C). Lower rates of elimination were found for the liver compared with muscle, the difference increasing with increasing temperature, while elimination rates from the serum were higher than those of other tissues, especially at the high temperature.     

Influence of environmental temperature and water oxygen concentration on gas diffusion distance in sea bass (Dicentrarchus labrax, L.)

Gas diffusion distance (GDD) of sea bass was measured in fish bred under farm conditions, at different dissolved oxygen concentrations (DO): normoxia condition (80–100% of the saturation value) and `mild' hyperoxia condition (120–130% of the saturation value). Measures were carried out two times in a year (beginning of summer and autumn) in order to evaluate the effect of water temperature on GDD at the two different dissolved oxygen concentrations. There was a significant influence of both dissolved oxygen concentration (p 0.001) and environmental temperature (p 0.001) on GDD. In summertime it was 1.75 m and 2.31 m for fish reared under normoxia and hyperoxia, respectively, and in autumn 2.51 m and 2.96 m for fish reared under normoxia and hyperoxia, respectively. When DO was reduced at the higher temperatures, GDD decreased as well. Results lead to the conclusion that GDD increased with the increasing of DO, both due to reduced water temperature and to the mild oxygen hypersaturation following application of pure oxygen. The advantage for fish may be found in the compromise between maximising O<sub>2</sub> diffusion at the gills and ions/water intake/loss, known as `osmoregulatory compromise'.     

Florfenicol depletion in edible tissue of rainbow trout,Oncorhynchus mykiss (Walbaum), and sea bream,Sparus aurata L.

An increase in fish production has consequently brought an increase in infectious diseases in fish farms. The use of chemotherapic drugs is the most effective instrument against common bacterial agents. The number of registered drugs for use in aquaculture is limited and often veterinary practitioners resort to the off‐label use of chemotherapic agents authorized for different food‐producing animal species. Florfenicol is well known for its outstanding effect against various pathogenic bacteria affecting fish, and therefore, it may be a useful drug for off‐label use in aquaculture. The aim of this study was to evaluate the depletion of florfenicol and its major metabolite, florfenicol amine, from the edible tissue of two fish species, rainbow trout and sea bream, following treatment with medicated feed at a dosage of 10 mg kg^?1 of bw day^?1, for 10 consecutive days. At prefixed time points after the end of administration (0.25, 1, 2, 3, 4, 6, 7, 10, 14 and 21 days after treatment), edible tissues (muscle plus adherent skin) from 15 individuals in each group were collected and analysed by HPLC, to determine concentration of the drug in the tissue. On the basis of the obtained concentrations, withdrawal times of florfenicol in the two species were calculated. The results indicate that a drug withdrawal time of 500 °C‐day, as established by Directive 2004/28/EC, for off‐label drug use is more than satisfactory to guarantee the healthiness of fish products against the risk of drug residues.     

The effect of demand feeding on swimming speed and feeding responses in Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages

Abstract Using underwater cameras, data were collected on the feeding behaviour and swimming speeds of Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages. Comparisons were made between the behaviours of fish fed on demand using interactive feedback systems and those of fish fed under the standard feeding practice of each farm (control). In all three species, swimming speeds were similar before feeding , but they were significantly higher in the control regimes during feeding. When fed on demand, sea bass had reduced swimming speed just before and during feeding compared with that observed during the non‐feeding periods. Higher proportions of feeding fish were observed in the control regime cages than in fish fed on demand for all three species, indicating a greater feeding intensity during meals in the control regimes. This was further supported by observations of an increase in the density of sea bass in the upper water in the control cages during feeding. The results suggest decreased levels of competition between the on demand‐fed fish during feeding, which might be hypothesized to lead to improved growth and production efficiency in aquaculture.     

Effects of dietary mannan oligosaccharides on growth,body composition and intestine of the sea bass (Dicentrarchus labrax L.)

The effect of Bio‐Mos incorporated into feed formulation on the growth, feed utilization, body composition and histological response of sea bass (Dicentrarchus labrax) was investigated. Final fish weight, feed conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), protein productive value (PPV) and energy utilization (EU) of sea bass feed Bio‐Mos supplemented diet and the control diet were determined at the end of experiment. Data present mean ± SD from triplicate determination (n = 3) for a 75‐day feeding trial. Different concentrations (0.5, 1.0, 2.0. 3.0 and 4.0 g kg diet^?1) of Bio‐Mos supplementation and a control without Bio‐Mos incorporation were fed to the fish, feed in the form of dry diets. Average final weight was significantly higher at 1.0 g kg diet^?1 of Bio‐Mos and lowest in control fish group; SGR significantly higher at the 1.0 g kg diet^?1 of Bio‐Mos. In addition,, PER, PPV and EU showed the same trend. The chemical body composition, crude protein, dry matter, crude fat and ash were significant (P ≤ 0.01) compared to control groups. We concluded that 1.0 g kg diet^?1 of Bio‐Mos improved the growth, feed efficiency, histology intestine and survival of sea bass.     

Study of liver and gut alterations in sea bream,Sparus aurata L., fed a mixture of vegetable protein concentrates

This study evaluated liver and gut alterations of gilthead sea bream, Sparus aurata L., fed diets in which fish meal was substituted by a mixture (M) of pea protein concentrate (PPC) and rice protein concentrate (RPC). Histological studies were conducted to evaluate the possible changes produced by four experimental isolipidic (18%) and isoproteic (48%CP) diets with 30%, 60% and 90% of fish meal substitution by a pea and rice mixture and compared with a control diet (0%). The results obtained in the present histological study showed significant changes especially in the case of the 90% substitution in parameters such as thickness of the layers, goblet cells and villi measurements. Structural integrity of the gut would not be significantly affected by a diet of up to 60% substitution. The alterations observed in the liver could not only be attributed to diet but also to possible individual variations.