Francesca Tulli

Digestibility of extruded peas, extruded lupin, and rapeseed meal in rainbow trout (Oncorhynchus mykiss) and turbot (Psetta maxima)

Apparent digestibility coefficients (ADC) of nutrients and energy of extruded peas, extruded lupin and rapeseed meals were determined in juvenile rainbow trout and turbot. Extruded lupin was found to be a promising substitute for fish meal in the diets of trout and turbot, with an acceptable digestibility of its dry matter (70% in trout and 81% in turbot) and a high digestibility of its protein (96% in trout and 98% in turbot) and its energy (77% in trout and 85% in turbot). Extruded peas had a lower digestibility of its protein in trout (88%) than in turbot (92%), and the ADC of energy, mainly supplied as starch, was relatively low (69% in trout and 78% in turbot). The digestibility of rapeseed meal was improved by a thermal treatment. Without thermal treatment, rapeseed meal had a low digestibility of its dry matter (57%) and energy (69%) in turbot. The availability of phosphorus was higher for extruded lupin (62% in trout and 100% in turbot) compared to the other plant-ingredients. When compared to a solvent-extracted meal, the availability of phosphorus from rapeseed meal was improved by heat treatment in both species (42% vs. 26% in trout and 65% vs. 49% in turbot).

Arginine requirement and effect of different dietary arginine and lysine levels for fingerling sea bass (Dicentrarchus labrax)

Groups of 60 European sea bass fingerlings weighing 2.1 ± 0.05 g/fish were kept in each of 18 flow-through 65-litre tanks supplied with 2.5 l/min of brackishwater (temperature, 25 Co; salinity, 25 ppt). Duplicate tanks were fed for 9 weeks with 9 isonitrogenous (46 ± 0.2%; N × 6.25) and isolipidic (12 ± 0.2% by ether extract) semipurified diets obtained from a basal mixture formulated to be limiting in arginine (1% by weight). The basal diet contained maize gluten meal (300 g/kg), herring meal (100 g/kg) and mixtures of indispensable and dispensable amino acids to simulate, excluding arginine and lysine, the amino acid profile of sea bass muscle protein. Seven diets were used to evaluate the arginine requirement. They were obtained by adding 0, 3, 6, 9, 12, 15 and 18 g/kg of pure l-arginine to the basal mixture while maintaining the lysine level equal to the sea bass requirement (2.2 g/100 g diet). Diets 8 and 9 were prepared to contain either a 50% excess or deficiency of lysine and a constant level of arginine (1.95 g/100 g diet). By analysis of the doseresponse relationship based on growth data, the dietary requirement of arginine was found to be 1.81 ± 0.005 g/100 g diet corresponding to 3.9 g/16 g N. A similar value was obtained when the 5-h (peak) postprandial plasma urea concentrations were regressed against the dietary level of arginine (1.78 ± 0.06 g/100 g diet), suggesting the possible use of this parameter to confirm the arginine requirement estimated by conventional growth experiments. From the results of the present experiment it would seem that sea bass fingerlings, like other warmwater fish species, are apparently not sensitive to moderate disproportions of dietary arginine and lysine.

Response of European sea bass (Dicentrarchus labrax) to graded levels of methionine (total sulfur amino acids) in soya protein-based semi-purified diets

The dietary methionine (Met) and total sulfur amino acid (TSAA) requirements of European sea bass (Dicentrarchus labrax) (initial body weight 13.4 (SD 0.2) g) were estimated in a 12-week dose-response experiment. Seven isonitrogenous (7.6 % DM) and isoenergetic (gross energy, 21.2 MJ/kg DM) diets, based on soya protein and crystalline L-amino acids containing graded levels of L-Met (1.6-16.2 g/kg) at a constant cysteine (4 g/kg) level and a fish meal-based diet, were fed each to triplicate groups of fifty fish kept in 250 litre tanks in a thermoregulated (23 +/- 0.5 degrees C) seawater system. The Met and TSAA-deficient diet resulted in higher mortality, impaired feed intake and growth relative to the other treatments (P < 0.01). No signs of lens opacity due to limiting Met intake were observed and no feed intake or growth depression occurred at the highest level of dietary TSAA. Met and TSAA requirements for optimal N deposition or weight gain as fitted with the broken-line model resulted in estimated values of 8.0 and 12.0 g/kg diet (for example, 1.8 and 2.7 % dietary protein) and 9.1 and 13.1 g/kg diet (for example, 2.0 and 3.0 % dietary protein), respectively. Plasma levels of Met, homocysteine and cysteine increased in response to excess dietary TSAA, corroborating requirement estimates from growth data. N gain resulted in a linear function of TSAA consumption at marginal Met (TSAA) intake. The TSAA intake needed to maintain N balance resulted in a value of 20.0 mg TSAA/kg average body weight0.75 per d, which represents 23 % of the total (maintenance+accretion) requirement.

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.

Stable isotope ratio analysis as a tool to discriminate between rainbow trout (O. mykiss) fed diets based on plant or fish-meal proteins.

The use of stable isotope ratio analysis (SIRA) as a rapid analytical tool to characterize and discriminate farmed fish on the basis of the feedstuffs included in the diet formulation is discussed. Two isoproteic (44.8%) and isolipidic (19.6%) extruded diets were formulated: a fish-meal-based diet (FM diet), containing fish meal as the sole protein source; a plant-protein-based diet (PP diet), where pea protein concentrate and wheat gluten meal replaced 80% of fish meal protein. The diets were fed to eight groups of rainbow trout (initial body weight: 106.6g) for 103 days in two daily meals under controlled rearing conditions. Growth performance (final body weight: 318.5 g; specific growth rate: 1.06%) and feed-to-gain ratio (0.79) were not affected by the dietary treatment. The differences in isotopic values of the two diets were clearly reflected in the different carbon and nitrogen isotopic values in rainbow trout fillets. The delta(13)C and delta(15)N values of muscle of farmed rainbow trout showed differences between farmed fish fed a fish-protein-based diet (-20.47 +/- 0.34 and 12.38 +/- 0.57 for delta(13)C and delta(15)N, respectively) and those fed a plant-protein-based diet (-23.96 +/- 0.38 and 7.15 +/- 0.51 for delta(13)C and delta(15)N, respectively). The results suggest that SIRA provides a robust and verifiable analytical tool to discriminate between fish fed on a plant or a fish protein diet.

Seasonal changes in technological and nutritional quality of Mytilus galloprovincialis from suspended culture in the Gulf of Trieste (North Adriatic Sea).

Nutritional quality parameters, microbiological and technological quality indicators (condition index, meat yield and water-holding capacity) of blue mussel, Mytilus galloprovincialis, reared in the North Adriatic Sea were characterised at monthly intervals over a 1 year period. Contents of protein (7.5-11.6 g/100 g), lipid (1.0-2.2 g/100 g) and ash (2.2-3.3 g/100 g) varied significantly accordingly to condition index (6-15%). n-3 PUFAs were the predominant fatty acids (38.7-45.9% of fatty acids) and docosahesaenoic and eicosapentaenoic acids were the most abundant (167 and 93.3 mg/100 g, respectively). Glycine, glutamic and aspartic acids accounted for 40% of total amino acids. All samples exhibited limited concentrations of Cr, Mn, Ni, Cu and Zn, as well as Na. M. galloprovincialis from the North Adriatic Sea showed the highest technological and nutritional quality, considering also the inter-annual variability, in late spring, which corresponds to the period immediately before gamete release.

The effect of slaughtering methods on actin degradation and on muscle quality attributes of farmed European sea bass ( Dicentrarchus labrax )

In the current study, two different slaughtering procedures, spiking vs immersion in water/ice slurry, were applied on electrically stunned European sea bass (Dicentrarchus labrax) and the effects on actin degradation and fillet quality attributes were investigated. Rigor mortis index was similar for the two slaughtering techniques, whereas the shear force measurement indicated that rigor mortis occurred more quickly and intensely in the water/ice handled fish than in those slaughtered by spiking. The water/ice immersion procedure also resulted in higher amount of actin fragments than spiking. Muscle tissue apparent viscosity and water holding capacity were lower in sea bass treated in water/ice slurry compared with fish handled by spiking, whereas the acidification patterns of the two groups were not easily distinguishable. In conclusion, spiking appeared to preserve actin integrity better that water/ice and it seemed to ensure less muscle damage as indicated by the higher viscosity and water holding capacity values. Finally, a role of actin as a biochemical marker for the prediction of fish quality was suggested.

Biometry traits and geometric morphometrics in sea bass (Dicentrarchus labrax) from different farming systems

Abstract The effect of the farming system on biometry traits and dressing out yield were investigated in market-size European sea bass (Dicentrarchus labrax) cultured extensively or intensively in sea cages or land-based basins. Fish external appearences and shapes were studies with geometric morphometrics in order to assess the potential of combined methodologies in the assessment of finfish quality. Both standard biometry and geometric morphometrics were able to discriminate between sea bass farmed extensively from those cultured under intensive conditions. Geometric morphometrics has been shown to be a valuable tool for describing changes in shape features and could result a useful technique to be associated to biometry traits in the context of fish quality assessment.

Somatic indexes, chemical-nutritive characteristics and metal content in caught and reared sharpsnout seabream (Diplodus puntazzo)

Abstract The aim of this study was to compare some somatic indexes, chemical-nutritive characteristics and the contents of some metals (Pb, Cu, Cr and Zn) in the whole body and fillet from caught and reared sharpsnout seabream (Diplodus puntazzo). The fish came from three different conditions: reared in marine cages (R), captured in a natural lagoon (L) and in the Mediterranean sea (S). Thirty fish per group, divided into three weight categories (100±15.3, 200±18.7 and 300±20.4g), were used for the trial. Reared sharpsnout seabream showed higher amounts of celomatic fat (3.41%, 2.43%, 0.21%, respectively for R, L and S) and total lipid (13.86%, 11.23% and 5.06% respectively for R, L and S), and lower moisture (64.14%, 65.54%, 71.53%) and protein (17.73, 19.03 and 19.17%) than those caught in the lagoon and sea. The whole body of reared fish contained lower amounts of lead (0.70, 0.75 and 0.97mg/kg, respectively for R, L and S), copper (0.15, 0.38, 0.25mg/kg) chrome (2.19, 3.52, 3.77mg/kg) and higher zinc contents (63.47, 53.42, 47.31mg/kg) than caught fish. Fatty acids from sharpsnout seabream fillets showed a high lipid quality as confirmed also by low values of Thrombogenic index (0.36, 0.30 and 0.22, respectively for L, S, R) and Atherogenic index (0.47, 0.42 and 0.33, respectively for L, S, R). Reared sharpsnout seabream showed lower saturated fatty acid values (26.44%, 32.21%, 34.85%, respectively for R, S, L) and higher oleic acid amount (21.61%, 19.15%, 11.99%, respectively for R, L and S). The subjects captured in the sea had a higher arachidonic acid content (5.44%, 1.76%, 0.59%, respectively for S, L, R). In the weight categories, the 100g subjects, showed higher incidence of viscera (VSI: 4.32%, 3.12% and 2.92%, respectively for 100, 200 and 300g) and liver (HIS: 2.20%, 1.97%, and 1.77%, respectively for 100, 200 and 300g), higher moisture (69.49%, 67.03%, 64.69%) and lower lipid rate (7.64%, 10.18%, 12.32%).

Varying plant protein sources in the diet of sea bass Dicentrarchus labrax differently affects lipid metabolism and deposition

Abstract The liver activity of lipogenic enzymes, the lipid content in various tissues, and plasma lipid levels of major, were measured in sea bass (D. labrax) fed over 96 days either a, fish meal-based control diet or preparations where 70% of fish meal protein was replaced by wheat gluten singly or in combination with pea or soybean meals. Relative to the controls, sea bass fed the wheat gluten-based diet resulted in stimulated lipogenesis in liver and increased lipid deposition in muscle. The opposite occurred when a substantial amount of soybean meal was included in the diet. Mesenteric fat depots were apparently insensitive to major changes in dietary protein source in fish showing similar intakes of digestible protein, energy and lipid. These results confirm that varying plant protein source in the diet differently affects lipid metabolism and deposition in sea bass.