B.M. Poli

Fish welfare and quality as affected by pre-slaughter and slaughter management

Abstract. A reliable assessment of animal welfare-suffering and of its impact on product quality requires a multidisciplinary approach that takes into account fish behaviour and the different biochemical and physiological processes involved. This might be done by the contemporary study of changes of indicators of brain function, endocrine responses, post mortem tissue biochemical processes and quality changes. This work reviewed some of the most used indices of stress at the time of slaughter, commercial slaughter methods and related stress effects on physical and biochemical parameters of fish quality. The set of the available data seemed to indicate that, although of some results appear contradictory, pre-slaughter and slaughter stressful practices could have an important effect on the flesh quality in fish. A clear effect emerged mostly on the physical properties of flesh, because severe stress at slaughter time exhausted muscular energies, produced more lactic acid, reduced muscular pH, increased the rate of rigor mortis onset. In this way they could have significant negative effects on technological traits, flesh quality and keeping quality of fish. Asphyxia and electrically stunned fish were more stressed than spiked, knocked and live chilled fish. Combining various methods together might be a more satisfactory strategy for both animal welfare and product quality.

The effects of dietary fat and NFE levels on growing European sea bass (Dicentrarchus labrax L.). Growth rate, body and fillet composition, carcass traits and nutrient retention efficiency

European sea bass (91.5 ± 5.7 g) were randomly assigned to 12 tanks (25 fish/tank) and fed six experimental diets for 224 days according to a 3 X 2 factorial design [three crude fat levels: 11, 15 and 19% on dry matter basis, dm; 2 N-free extract (NFE) levels: 21.5 and 28.5% dm], with two replicates for each treatment. Daily feeding rate was 0.95% live weight. Final weight (339.9 g) and daily energy (11.78 kJ/fish) and protein gain (200 g/fish) were significantly higher for fish fed diets containing 19% fat. The whole body of the fish fed diets with the highest crude fat and NFE levels had significantly lower contents of moisture and protein and a higher level of crude fat. Body ash and P contents (4.41 and 0.7% wet weight) did not differ among treatments. Gross energy, protein and phosphorus retentions (29.2, 19.0 and 32.6%, respectively) and dressing percentage (89.4%) were not affected by treatments. HSI significantly decreased as dietary fat levels increased, only in fish fed diets with the highest amount of NFE. Liver fat content was significantly greater in the fish fed the highest level of NFE (35.2%) in comparison with those fed the lower level of NFE (26.0%) (P < 0.05). Percentage head and viscera (without liver) significantly decreased while percentage mesenteric and perinephric fat significantly increased with dietary fat content. Fillet percentage was significantly lower (44.1%) in fish fed diets containing 21.5% NFE, compared with those fed diets with 28.5% NFE (44.9%). Moisture decreased and lipid content increased in fillet of fish fed diets with 28.5% dietary NFE level, as dietary fat level increase. The saturated, monunsaturated and n - 6 polyunsaturated fatty acids of fish muscle significantly decreased while n - 3 PUFA levels significantly increased with increasing dietary fat content.

Preliminary results on quality and quality changes in reared meagre (Argyrosomus regius): body and fillet traits and freshness changes in refrigerated commercial-size fish

Meagre (Argyrosomus regius) intensively reared in tank by a Tuscany farm and fed commercial diets, were examined to study a) marketable and flesh nutritional traits in commercial-size fish and b) loss of freshness under refrigerated storage condition. Eighty fish, sampled in May, July and November (at 24, 26, 30 months of age) were submitted to linear measurements and weight of the most important body components. Whole fillets were analysed for moisture, lipid and fatty acid composition. Data were analysed by ANOVA (sampling date). A sub sample of fifty-four meagre (902–1840 g b.w.) was stored at 1 °C with ice cover and evaluated every 24 h after death until spoilage for the EU freshness classes, dielectric properties, rigor index, muscular and eye liquor pH, K1% freshness index. Data were analysed by regression on time after death. A small sample of meagre (n = 6) and sea bass (Dicentrarchus labrax) (n = 6), reared in analogous rearing condition in the same farm were compared by ANCOVA on body weight (average b.w. 668 g). Meagre were characterised by 1.04 condition factor, 44% fillets, 6% viscera, negligible mesenteric fat (≅1%) and 94.5% dressing yield. The head incidence increased (P < 0.01) with b.w. increase. Moisture increased while lipid decreased (P < 0.01) in fillet from July to November (74.47 vs 75.96%; 2.93 vs 2.06%). An index of thrombogenicity calculated from the quantitative fatty acid composition was very low (0.10). In comparison with sea bass of the same body weight, meagre had greater length (41.2 vs 37.6 cm), head incidence (29.9 vs 20.7%) and dressing (94.8 vs 89.2%) and lower viscera (5.2 vs 10.9%), mesenteric fat (0.9 vs 7.9%) and intramuscular fat (2.24 vs 12.78%) incidences. Meagre had a 9-day shelf-life (E class from 1st to 3rdd and A class from 4th to 7thd). Rigor index and impedance remained higher than 90% and 66, respectively until the 3rdd after death. The quality traits found for this species indicated meagre as a promising candidate for Mediterranean aquaculture.

Quality outline of European sea bass (Dicentrarchus labrax) reared in Italy: shelf life, edible yield, nutritional and dietetic traits

Abstract The final product quality of European sea bass was outlined through some results on (1) quality traits in a large range of body size (80–1580 g weight) and (2) changes in sensorial and objective quality parameters during shelf life, as influenced by the rearing system, storage and stress. More than 500 European sea bass of commercial size were used in several trials. All fish were subjected to linear and weight measurements. In most trials, sea bass were stored at 4 or 1 °C with ice cover and evaluated every 24 h after death until spoilage for the EU freshness classes and for a large number of physical and chemical quality traits (rigor index, dielectric properties, muscle and eye liquor pH, water-holding capacity (WHC), water, protein, ash, total, neutral and polar lipids, cholesterol, fatty acids, malonaldehyde, adenine nucleotides and biogenic amines). Fillets showed on the average isometric growth, but the dorsal muscle grew faster and the ventral one slower than the body weight. A moderate corpulence increase in fish shape during growth emerged. The size range from 500 to 940 g—when incidences of fillets and dorsal muscle were higher than 48% and 31% and that of viscera was lower than 10%—can be suggested for having sea bass with the better edible portion yield. Protein and ash contents of muscle remained constant with body weight increase, while moisture and cholesterol content decreased; total lipid moderately increased along with the triglyceride incidence. On the whole, the muscular fatty acid pattern determined good indexes of atherogenicity (IA) and mostly of thrombogenicity (IT). Sea bass stored at 4 or 1 °C with ice cover had a 6- and 10-day shelf life, respectively. In the first 2 and 3 days, respectively, sea bass were Extra (always with 100% rigor index) and had Fish Tester values decreasing to 64 or 73, respectively, and negligible levels of malonaldehyde (MDA) and biogenic amines. In the following 2 and 3 days, respectively, sea bass became A fish (good quality), with decrease of rigor index (IR) and Fish Tester (FT) and slight increase in malonaldehyde and putrescine contents. In the following 2 and 4 days, respectively, sea bass became B fish (bad quality), with further decrease of rigor index and Fish Tester and moderate increase of malonaldehyde and putrescine. Thereafter, fish were unfit for human consumption. No difference in quality parameter of fish reared in aerated (4.3 ppm O2) or hyperoxic (9.3 ppm) conditions was found. Stress shortened the pre- and post-rigor phase and shelf life.

Use of fresh and preserved Tetraselmis suecica for feeding Crassostrea gigas larvae

Abstract In an attempt to provide cost-effective alternative diets and to simplify hatchery–nursery procedures, substitutes for live microalgae in mariculture were tested and among them, concentrated microalgae have so far appeared to be the best alternative products for bivalves, though there are few experimental studies. The food quality of fresh and preserved Tetraselmis suecica for umboned Crassostrea gigas larvae was studied here and its potential as an algal feed for remote production was evaluated. Because it leads to lower growth and higher mortalities than the control diets (>60%), the use of T. suecica OR (strain Orbetello) for C. gigas larvae is not recommended as a monospecific diet. However, a binary diet that includes T. suecica OR is as efficient as the standard ternary PTC diet for C. gigas larvae. On the other hand, even though microalgal utilisation was not clearly affected by the initial size of the larvae, it seemed that old umboned larvae took full advantage of T. suecica OR. Its usefulness in C. gigas larval rearing is therefore limited, but its potential for oyster spat feeding has to be considered. Lastly, preservation at low temperature is an efficient method to maintain the food value of T. suecica OR.

Farmed fish welfare-suffering assessment and impact on product quality

Abstract Fish welfare, suffering and the perception of pain were debated, together with several factors reducing infra vitam welfare of farmed fish (genetic, environment, density, malnutrition, starvation, cataracts, deformities, vaccination side effects, transport, handling, confinement, crowding, harvesting, killing method). Behavioural and physiological stress responses were considered as indicators of welfare reduction. The effects of pre-slaughter management practices, and the most commonly used stunning/slaughtering methods on welfare and quality reduction of farmed fish were discussed. A number of indicators can be used to assess fish welfare-suffering, both in a scientific and practical context, such as behavioural, haematic, cellular, tissue post mortem fish stress and quality indicators, but none of them are optimal. The best strategy for a reliable assessment of fish welfare/suffering and their impact on product quality is a multidisciplinary approach that takes into account animal behaviour and the different biochemical and physiological ante mortem and post mortem processes involved: several components, all influenced in a similar way by the same condition, suggest real welfare and quality reduction.

Body traits and chemical composition of muscle in the common carp (Cyprinus carpio L.) as influenced by age and rearing environment

To investigate body traits and muscle chemical composition in common carp as influenced by age and rearing environment, 2000 fry were stocked in two earthen ponds (300 m2): warm (W), with warm water (refluent from a thermal power station) at about 10 °C above natural temperature, and natural (N), with water from Lake Trasimeno. Because of the different growth rate, W subjects were sampled 3 times (at 12, 15 and 18 months of age) while N-subjects were sampled only once (at 15 months of age). The W 12-month-old fish weighed on average 102 g while N-fish did not reach this weight even at 15 months. At this age, the W subjects showed, in comparison with N-subjects, higher body weight (143 vs. 85 g), component weights, linear measurements (20.94 vs. 17.8 cm), fins (1.80 vs. 1.63g) and filleting remnants (12.80 vs. 11.25%) and lower incidence of skin and head index; no differences resulted in proximate analysis, but muscles of W-fish were richer in saturated fatty acid and in n − 3 PUFA content and showed a higher n-3n-6 PUFA ratio. By comparison with the 15-month-old subjects collected in October 1992, the 12-month-old W-subjects, collected in July 1992, showed lower fin (0.59 vs. 1.8%), viscera (7.6 vs. 10.2 %) and head (20.36 vs. 22.92%) percentages but higher gill (4.27 vs. 3.24%), filleting remnant (14.99 vs. 12.80%), skin (3.92 vs. 3.37%) and dressing (92.4 vs. 89.79%) percentages. The 18-month-old W-subjects, collected in January 1993, did not differ significantly from the 15-month-old subjects either in body weight (154 vs. 143 g) or in the other traits studied, excluding the incidence of viscera (12.01 vs. 10.21%) and gills (2.69 vs. 3.34%), respectively, in the older subjects. Intramuscular lipid content decreased from July according to a seasonal trend. Allometric coefficient showed tachyauxesis for viscera, pectoral and pelvic fins, skin and total muscle and bradyauxesis for filleting remnants and head.

Effect of the Inclusion of Dried Tetraselmis suecica on Growth, Feed Utilization, and Fillet Composition of European Sea Bass Juveniles Fed Organic Diets

Dried Tetraselmis suecica was evaluated as a fish protein substitute when incorporated to replace (protein basis) 10% (TETRA10) and 20% (TETRA20) of the control diet. The diets were offered to nine groups of European sea bass (72 g) over 63 days. Test diets did not affect zootechnical performances nor carcass or fillet yields and proximate analysis of edible portion. Feeding TETRA20 resulted in lower apparent digestibility coefficients of protein, lipid, and organic matter, and hepatosomatic index compared to the control diet. T. suecica was able to replace up to 20% of fish protein without hampering growth performance and major quality traits of sea bass.

Application of multivariate analysis to sensorial and instrumental parameters of freshness in refrigerated sea bass (Dicentrarchus labrax) during shelf life

Abstract Freshness by sensory analysis descriptors and instrumental parameters (rigor index (RI), dielectric properties, K1, compactness (IC) and resilience (IEL), pH, free water (FW), cooking losses (CL)) was evaluated in sea bass stored at 4 and 1 °C with ice covering. Sensory scores presented high values of repeatability (≥0.70). The Principal Component Analysis of sensorial parameters revealed that Factor 1, accounting for a 95% of the variation and linked to storage duration, displayed homogenous behaviour. An antithesis between descriptors of external characteristics of fish and those relative to internal parts was observed, particularly in the intermediate phase of the shelf life, during which storage temperature played a discriminating role. The PCA of the sensorial and instrumental parameters together showed that the parameters most correlated with the first factor (83% of overall variance) were the sensorial ones (loading scores >0.96), K1 freshness index, rigor index and dielectric properties (loading scores =−0.96, 0.73 and 0.71, respectively). Data suggest that the external characteristics of the fish alone could be used to measure freshness. The K1, rigor index and dielectrics properties could be used as objective measures of freshness. Sensory ratings are less powerful for freshness analysis at the later stages of shelf life.

Effect of Total Replacement of Dietary Fish Meal by Plant Protein Sources on Early post mortem Changes in the Biochemical and Physical Parameters of Rainbow Trout

The replacement of fish meal with plant protein sources is a major issue of interest in the aquaculture of Teleostei (Tacon, 1994). Although several studies have been undertaken over the last two decades, many questions remain about the feasibility of the total substitution of traditional protein sources. Moreover, the effects of the protein source on the quality characteristics of the product obtained have been little investigated (Médale, 2003). The aim of this study was to evaluate the effect of a diet based only on plant protein sources on the behaviour of some biochemical and physical parameters during the first 24 h after death.