E. Tibaldi

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.

Growth response of juvenile dentex (Dentex dentex L.) to varying protein level and protein to lipid ratio in practical diets

Abstract The dentex ( Dentex dentex L.) is a fast-growing sparid which represents a possible candidate for Mediterranean mariculture. As the basic nutrient requirements of this species are unknown, two feeding trials were carried out to identify suitable protein and lipid (energy) levels to be used in formulating practical diets for dentex. The experiments used groups of 30 specimens (each fish weighing 17 or 20.7 g) which were kept in 12 flow-through 160 1 tanks supplied with sea water at 2 1 min −1 (temperature 20 ± 1 °C; salinity 33 ppt). An initial 4-week trial was conducted to obtain a preliminary estimate of the optimal protein level. Triplicate groups were fed four practical diets with increasing levels of protein (44.3, 49.3, 55.7 and 58.9% dry matter (DM), over 90% of which was supplied by white fish meal) and a constant lipid content (17.3% DM; mostly supplied by fish lipids) to satiation. An analysis of the nutrient-weight gain relationship indicated that the optimal dietary protein level was 49.3% DM. In a second 60 day experiment, duplicate groups of fish were fed six diets with three protein levels (44.4, 49.5 and 55.8% DM) and two lipid contents (12.0 and 17.3% DM) within each protein level, nearly to satiation. Growth performance was lowest in fish given diets containing 44.4 or 49.5% protein and 12% lipid and was improved ( P −1 calculated available energy) could be assumed as suitable levels for formulating practical diets for this species, providing high quality fish meal and oil are used.

Abnormalities of the operculum in gilthead sea bream (Sparus aurata): morphological description

The authors studied a population of 582 gilthead sea breams (Sparus aurata), aged 25–600 days, in order to describe the abnormalities of the opercular complex. Particular attention was paid to: (1) the different degrees of abnormality of the opercular complex as a whole and of the individual dermal bones (preopercle, interopercle, subopercle and opercle) that compose it; (2) the ways in which the operculum folds into the gill cavity and the relevant histological characteristics. This study discusses the origin and nature of the abnormalities. Though these abnormalities have a major impact on market value and product image, and are often linked to other disorders in fish, they are still difficult to eliminate. Gaining a basic understanding of these abnormalities will be a first step towards reducing their occurrence. D 2003 Elsevier Science B.V. All rights reserved.

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.

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.

Effects of dietary nucleotides on acute stress response and cannabinoid receptor 1 mRNAs in sole, Solea solea

The objective of the present study was to evaluate the modulation of acute stress response by dietary nucleotides (NT) in sole, Solea solea. A basal diet was supplemented with levels of 0 (normal diet), or 0.4 g NT/kg dry diet for 8 weeks. At the end of feeding trial, fish fed the normal and NT-supplemented diet were subjected to a standardized protocol of disturbance and sampled over a 24h recovery after the stressor exposure. Modulatory effects of NT on acute stress response (cortisol and glucose), proopiomelanocortin (POMC) and cannabinoid receptor 1 splice variants (CB1A and CB1B) mRNA levels were studied. Both plasma cortisol and glucose levels of fish fed NT-supplemented diet were significantly lower than fish fed the control diet at 1 and 4h post-stress time-points. There are no significant effects of dietary NT on POMC and HSP70 mRNA levels. In our study, both CB1A and CB1B trascript levels were induced in fish fed the normal diet at 1 and 4h post-stress intervals. Collectively, the results obtained suggest that dietary NT modulates the CB1-like receptor mRNA expressions leading to attenuation in stressor-induced plasma cortisol level in sole.

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.

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.