Effect of Feeding Level on Nutritional Quality of ...

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Effect of Feeding Level on Nutritional Quality of Rainbow Trout (Oncorhynchus mykiss) Flesh a

Giovanni B. Palmegiano MSc , Marcella Boccignone a

b

MSc , Gilberto Forneris MVM , Franco Salvo MSc c

, Marisa Ziino MSc , Donatella Signorino MSc, PhD

c c

d

, Benedetto Sicuro MSc , Laura Gasco MAgrSc, PhD d

& Ivo Zoccarato MVM

d

a

CNR-Centro di Studio per gli Animali in Produzione Zootecnica, Via Nizza 52, 10126, Torino, (Italy) b

Dipartimento di Produzioni Animali, Epidemiologia ed Ecologia, Università di Torino, Via Nizza 52, 10126, Torino c

Dipartimento di Chimica Organica e Biologica, Università di Messina, Salita Sperone 31, 98100, Messina d

Dipartimento di Scienze Zootecniche, Università di Torino, Via L. da Vinci 44 10095 Grugliasco, Torino Version of record first published: 11 Oct 2008.

To cite this article: Giovanni B. Palmegiano MSc, Marcella Boccignone MSc, Gilberto Forneris MVM, Franco Salvo MSc, Marisa Ziino MSc, Donatella Signorino MSc, PhD, Benedetto Sicuro MSc, Laura Gasco MAgrSc, PhD & Ivo Zoccarato MVM (2000): Effect of Feeding Level on Nutritional Quality of Rainbow Trout (Oncorhynchus mykiss) Flesh, Journal of Agromedicine, 6:4, 69-81 To link to this article: http://dx.doi.org/10.1300/J096v06n04_08

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Effect of Feeding Level on Nutritional Quality of Rainbow Trout (Oncorhynchus mykiss) Flesh Giovanni B. Palmegiano, MSc Marcella Boccignone, MSc Gilberto Forneris, MVM Franco Salvo, MSc Donatella Signorino, MSc, PhD Marisa Ziino, MSc Benedetto Sicuro, MSc Laura Gasco, MAgrSc, PhD Ivo Zoccarato, MVM

ABSTRACT. The effect of different feeding levels (1.2%, 1.4%, 1.8% and to satiety) on the growth skill, morphological indexes and chemical composition of the dorsal muscle of rainbow trout (Oncorhynchus mykiss) have been investigated. Significant differences were observed for Giovanni B. Palmegiano and Marcella Boccignone are Researchers, CNR-Centro di Studio per gli Animali in Produzione Zootecnica, Via Nizza 52, 10126 Torino (Italy). Gilberto Forneris is Associate Professor, Dipartimento di Produzioni Animali, Epidemiologia ed Ecologia, Università di Torino, Via Nizza 52, 10126 Torino. Franco Salvo and Marisa Ziino are Associate Professors, Dipartimento di Chimica Organica e Biologica, Università di Messina, Salita Sperone 31, 98100 Messina. Donatella Signorino is affiliated with the Dipartimento di Chimica Organica e Biologica, Università di Messina, Salita Sperone 31, 98100 Messina. Benedetto Sicuro and Laura Gasco are Researchers, Dipartimento di Scienze Zootecniche, Università di Torino, Via L. da Vinci 44, 10095 Grugliasco (Torino). Ivo Zoccarato is Associate Professor, Dipartimento di Scienze Zootecniche, Università di Torino, Via L. da Vinci 44, 10095 Grugliasco (Torino). Address correspondence to: Ivo Zoccarato, Dipartimento di Scienze Zootecniche, Università di Torino, Via L. da Vinci 44, 10095 Grugliasco (Torino). Research partially supported by grant ‘‘Quota ex 60%, 1998.’’ Journal of Agromedicine, Vol. 6(4) 2000 E 2000 by The Haworth Press, Inc. All rights reserved.

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JOURNAL OF AGROMEDICINE

the morphological indexes which increased with feeding level. For instance, the increase of feeding level induces a decrease in moisture content in the muscle composition, which corresponds to an increase of fat. Feeding level modified phospholipids, triglycerids and fatty acids content. These results can be of potential interest for the consumer from a diet point of view, and for the fish processing industry, since the processing and safe preservation of finished products are strictly linked to the chemical characteristics of fresh product. [Article copies available for a fee from The Haworth Document Delivery Service: 1-800-342-9678. E-mail address: Website: ]

KEYWORDS. Trout flesh, feeding level, fatty acids profile, nutritional value

INTRODUCTION Changes in lifestyle have seen an increased interest in healthy diets. Usually, foods of animal origin and their excessive intake are considered factors inducing serious human illnesses. Fish is seen as an important food because of its high ratio of saturated/unsaturated fatty acids and in particular for the presence of acids such as eicosapentaenoic (EPA: C20:5 n3) and docosahexaenoic (DHA: C22:6 n3).1,2 In this context, fish are seen as important in the prevention of cardiovascular diseases. The nutritional features of fish are fundamental in the choice of a modern healthy diet. With this in mind, food industries are becoming involved more with quality rather than quantity; similarly, fish farmers cannot escape the new requirements imposed by the market. Many management factors can influence and determine the qualitative traits of fish. In fish of the same size, feed characteristics directly affect the chemical composition of the finished product, which can be further affected by the level of feeding or fasting.3-5 To define the quality of food, fish or meat, is very difficult, since the quality is the result of a balance of different parameters, some intrinsically linked to the product, such as taste, color, smell, and others related to the post-mortem processing as salting, smoking, or canning, which have an effect on the general aspect of the product. Last but not least is the ability of the consumer to assess quality. It should be stressed that it is necessary to produce not only fresh food for direct consumption, but also raw material suitable for proc-


Reviews, Case Histories, and Research

71

essing (filleting, smoking, etc.). However, if the chemical composition of flesh alone cannot define the quality of the fish,6 it can provide primary information on the type of fish that has been processed. In particular, on the basis of the differences in the fatty acids profile, it is possible to differentiate various fish species (marine or freshwater), and to determine whether they were caught or farmed.7,8 Even if the close relationship existing between feeding level, body composition and performances is well-established, the recent developments in feeding technology and the availability of fast-growing selected strains of salmonids questions this relationship, where an unfavourable genetic correlation exists between body weight and the percentage and area of fat deposition exists.9 The aim of this research is to evaluate the effects of different feeding levels on the chemical composition of rainbow trout (Oncorhynchus mykiss) fillet.

MATERIALS AND METHODS Chemical composition and fatty acids profiles of the dorsal muscle of rainbow trout were determined on samples obtained from fish bred at a temperature of 12-13_C, with a water flow of 30 l/min and a dissolved oxygen of 7.2 mg/l. Live weight of trout before slaughtering ranged between 180 and 250 g. All trout were fed the same and unique batch of commercial pelletized diet (% on wet/weight: moisture 9.5; crude protein 42.5; ether extract 10.6; crude fiber 1.5; ash 7.3; gross energy 19 MJ/kg; components in decreasing order: fish meal, meat meal, soybean meal, blood meal, dried fish soluble, dried yeast, pregelatinized starch, wheat meal, fish oil) according to four feeding levels: 1.2%, 1.4%, 1.8% of the fish biomass and to satiety. The fatty acid profile of diet is reported in Table 1. In the case of the restricted feeding levels feedstuff was delivered twice a day, whereas trout fed to satiety received diet until refused twice a day. Each treatment was replicated three times. Trout were fed for 13 weeks. Thirty trout for each treatment were slaughtered and eviscerated. Hepatosomatic index (HSI = liver to body weight ratio 100), viscerosomatic index (VSI = viscera to body weight ratio 100), and fat coefficient (CF = visceral fat to body weight ratio 100) were calcu-



72

TABLE 1. Fatty acids profile of diet (g/100 g total fatty acids). C14:0 C15:0 C16:0 C16:1 n7 C16:2 n4 C16:3 n4 C17:0 C18:0 iso C18:0 C18:1 n9 C18:2 n6 C18:3 n3 C18:4 n3 C20:1 n9 C20:5 n3 C22:1 n11 C22:6 n3 Saturated Monounsaturated Polyunsaturated n3 n6 n3/n6

5.133 0.521 23.774 6.319 0.173 0.142 0.349 0.339 4.383 22.646 15.384 0.833 1.823 3.670 5.577 5.307 3.619 34.162 37.943 27.554 11.854 15.384 0.770

Total lipids (w/w)

10.6

lated. Chemical composition of fillets (raw proteins, total lipids and ash) was obtained according to A.O.A.C. rules.10 Saturated/unsaturated fatty acids ratio (S/P), atherogenicity (IA) and thrombogenicity (IT) indexes were calculated in according to Ulbricht and Southgate11 as following: SńP +

C 14:0 ) C 16:0 ) C 18:0 MUFA ) PUFA

i ii iii IA + aS ) bS ) cS dP ) eM ) fMȀ

Where: Si = C12:0; Sii = C14:0; Siii = C16:0; P = sum of n6 and n3 PUFA M = oleic acid (C 18:1) Mi = sum of other MUFA a, b, c, d, e, f = empirical constants: b = 4 a, c, d, e, f = 1



IT +

73

mS iv nM ) oMȀ ) p(n6) ) q(n3) ) (n3ńn6)

Where: Siv = sum of C 14:0, C 16:0 and C 18:0 n6 = n6 PUFA n3 = n3 PUFA M and Mi are as before m, n, o, p, q = empirical constants: m = 1 n, o, p = 0.5 q=3 Fatty acids profiles were determined on dorsal muscle. Weighed samples were minced, homogenized and extracted with a mixture of chloroform/methanol (2:1 v/v) according to Folch et al.12 Small portions (25 mg) of the extracted lipids were dissolved in hexane and separated into lipid classes by thin layer chromatography, on 20 cm 20 cm TLC glass plate coated with a layer (0.05) of silica gel G (E. Merck) using hexane/diethyl ether/formic acid (80/20/2) as the solvent system. Lipid classes were detected by spraying with 2,7-dichlorofluorescein (0.2% in ethanol), and by inspection under long-wave UV light. The classes were identified by comparison with authentic lipid standards. Four classes have been isolated, with decreasing retention factors: triacylglycerol, free fatty acids, sterols and phospholipids. The classes were then quantified by gas chromatography. Weighed portions of the isolated lipid classes were converted to fatty acid methyl esters (FAMEs) by direct transesterification with refluxing methanol/1% sulphuric acid under an argon atmosphere. The methyl esters thus obtained were separated from other by-products and purified by column chromatography (silica gel, dichloromethane/ ether 10:1). FAMEs were then analyzed by gas-chromatography with a DANI 86.10 Gas Chromatograph equipped with a hydrogen flame ionization detector (FID), with a 30 m 0.32 mm i.d. fused silics capillary column Omegawax 320 (Supelco) having a 0.25 mm film thickness. Oven temperature was programmed from 160_ to 190_C at 2.0_C/min and then 190_ to 230_C at 4.0_C/min. The injector had a split ratio of 100:1; injector and detector temperatures were 265_C and 275_C, respectively. Hydrogen was employed as carrier gas, with a flow rate of 2.2 m/min measured at the initial temperature of 160_C. The individual FAMEs were identified by comparison with the reten-



74

tion times of standard mixtures (Supelco PUFAs 1-2 and Menhadem Oil Test Mix), peak areas were automatically integrated and data were recorded with a Hewlett-Packard 3394 integrator. Data were evaluated by analysis of variance according to the GLM model.13 Significant differences at 5% level were determined by Duncan test. RESULTS AND DISCUSSION The values of trout live weight and morphological indexes observed at the different feeding levels are reported in Table 2; the relationships existing between the feeding levels and the indexes is evident, in fact feeding level affected the final live weight that grew with the quantity of feed distributed. Individual mean live weight at slaughter ranged between 180 and 280 g per trout. The indexes increased with the increase of feeding level. Fat tissue was stored mostly in the abdominal cavity as perivisceral fat. The chemical composition of trout fillets is shown in Table 3. It is possible to observe that the values reported are in agreement with those described by other authors.3,14 With the increase of feeding level TABLE 2. Morphologic indexes (mean " s.d.). Feeding level

LW (g)

1.2% 1.4% 1.8% to satiety

180 b 200 a 250 a 281 a

HSI 1.00 " 0.07 b 0.97 " 0.06 b 1.17 " 0.05 ab 1.20 " 0.06 a

VSI 6.05 " 0.37 c 6.41 " 0.34 b 7.98 " 0.36 a 8.99 " 0.30 a

CF 0.94 " 0.19 c 1.12 " 0.18 bc 1.59 " 0.18 b 2.49 " 0.19 a

Means in the same column with different letters are significantly different (P v 0.05)

TABLE 3. Chemical composition of trout fillets (% dry matter, mean " s.d.). Feeding level 1.2% 1.4% 1.8% to satiety

Water

Protein

Ether extract

Ash

80.08 " 1.43 a 78.65 " 1.35 b 78.08 " 1.32 b 76.24 " 1.28 c

16.51 " 0.66 a 16.94 " 0.62 ab 17.04 " 0.61 ab 17.53 " 0.66 b

1.79 " 0.42 b 3.71 " 1.93 a 3.82 " 0.14 a 4.08 " 0.63 a

1.39 " 0.14 a 1.33 " 0.08 a 1.45 " 0.10 b 1.48 " 0.16 b




75

a significant decrease in water content is observed, whereas fat and protein contents significantly increase between 1.2% and satiety feeding rate. This confirms what reported by Siliprandi and Siliprandi15 about the energy sparing process in fish: the water substitution by fat not only provides fish with floatation material, but also minimises osmoregulation processes. Moreover a high correlation between fish size and muscle lipid content exists, as observed in Atlantic salmon.16 Storebakken et al.,4 studying the nutritional partitioning in rainbow trout fasted or fed at different feeding levels, observed an increase in lipid content, proportional to feed intake both in muscle and viscera tissues. Furthermore, a decrease in the protein content was observed in the viscera. However, the greatest changes were found in the lipid fraction. In our case, the increase in protein content of muscle could be due to the fact that chylomicrons that distribute the triacylglycerol fatty acids to tissues, contain an amount of lipoproteins.17 Then, the high lipid deposit can indirectly induce an increase of protein content. It can also be inferred that the increase of fat deposit could be linked to an hyperplasia of adipocytes that could determine, as observed in terrestrial animals,18 an increase of protein content. On the basis of the information reported in literature, we can argue that the quantity of fat detected in our sample is not enough to interfere with processing and preservation of trout. In fact, Meizies and Reichwald,19 studying the effect of smoking, report a large variation in fat content in different fish, ranging from 3.3% for sturgeon to 24.5% for eel. Manthey et al.20 working on European catfish processing had very good results for sensory panel test on smoked fillets having a fat content of 4.4% on fresh matter. From the point of view of dietetic features, the different lipid classes reported in Table 4 show a significant increase of intramuscular triglycerid (TG) with the increase of feeding level while free fatty acids (FFA) and phospholipids decrease, but the difference is statistically significant only at satiety feeding rate. Relative to FFA, the values observed are higher in comparison with those observed by Ingemansson et al.21 in farmed rainbow trout. This situation could be due to a high hydrolysis of polar lipids that could be occurred in sample frozen before the lipid classes determination; this is also supported by the fact that phospholipids decrease. Orlick et al.22 report


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JOURNAL OF AGROMEDICINE TABLE 4. Lipid classes (% of total) (mean " s.d.).

Feeding level 1.2% 1.4% 1.8% to satiety

TG

FFA

Phospholipids

42.07 " 4.19 a 36.83 " 5.13 a 55.45 " 5.13 ab 60.44 " 4.44 b

11.47 " 4.06 a 12.17 " 1.31 a 9.98 " 2.79 ab 8.23 " 2.75 b

25.07 " 2.50 a 31.57 " 3.06 a 17.98 " 3.06 ab 14.99 " 2.65 b


the same fact for other species as cod and saithe. The increasing of TG and the decreasing of FFA observed with the increase of feeding level can be justified by the fact that, in fish fed to satiety, the lipase that split TG in mono- and diglycerid, is very active in the breakdown and absorption of fat that is metabolised as FFA. The high percentage of FFA inhibits the enzyme blocking the FFA liberation but not the TG absorption. It is important to highlight that, in the muscular tissue the lipid hydrolysis is a common postmortem feature in fish and fish products. Its effect is undesirable and FFA, if present over a certain concentration, are usually removed before further processing. Some authors have reported that lipid oxidation occurs more rapidly in tissue containing more FFA and this may represent a secondary effect of lipid hydrolysis. This process of both triglycerids and phospholipids is normally a stepwise modification. Thus the initial reaction of lipase with triglycerids is with the primary alcohol ester group and then rather more slowly with the secondary alcohol ester group so that a mixture of glycerides, FFA and glycerol is produced.23 Fish fed to satiation provide a better product as the FFA level is lower and then the lipid tissue is more resistant to the oxidation. As reported in Table 5, the profile of fatty acids of total lipids show significant differences between the two lowest feeding levels for C 18:0 and C 20:5. Instead, the differences between the low and the high feeding levels are significant, in fact, it appears that with the increase of feeding level some saturated fatty acids decrease (C 16:0), while monosaturated fatty acids increase both as total value or considering the most significant (C 16:1 n7, C 18:1 n9). The level of C 20:5 n3 appears higher in 1.4% feeding rate than in other treatments. The lowest value of monounsaturated sum is reached in 1.4% treatment which is significantly different from 1.8% and to



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TABLE 5. Profile of fatty acids of dorsal muscle (mean " s.d.) (g/100 g total fatty acids). Diet Feeding level

1.2%

1.4%

1.8%

to satiety

ACIDS Saturated C14:0 4.17 " 0.81 C15:0 0.43 " 0.06 C16:0i 0.10 " 0.00 C16:0 29.00 " 2.62 a C17:0i 0.05 " 0.07 C17:0 0.33 " 0.21 C18:0 6.43 " 0.64 a C20:0 0.23 " 0.06 C22:0 0.10 " 0.00 C24:0 0.10 " 0.00 Monounsaturated C14:1 0.15 " 0.07 C15:1 trace C16:1n7 5.27 " 0.91 b C17:1 0.35 " 0.07 C18:1n9 17.60 " 3.06 b C18:1n7 3.30 " 0.52 C20:1 2.80 " 0.75 C22:1 1.97 " 0.74 C24:1n9 0.67 " 0.32 Polyunsaturated n3 C18:3 0.50 " 0.30 C18:4 0.60 " 0.10 C20:3 0.23 " 0.23 C20:4 0.43 " 0.15 C20:5 3.03 " 0.91 b C21:5 0.15 " 0.07 C22:5 1.03 " 0.15 C22:6 13.67 " 6.09 Polyunsaturated n6 C18:2 6.10 " 1.00 b C18:3 0.13 " 0.06 C20:2 0.43 " 0.06 C20:3 0.27 " 0.06 C20:4 0.75 " 0.35 C22:4 0.20 " 0.14 C22:5 0.15 " 0.07 Saturated 40.80 " 3.80 Monounsaturated 31.93 " 5.17 Polyunsaturated 27.27 " 8.91 n3 19.60 " 7.52 n6 7.67 " 1.39 n3/n6 2.50 " 0.46 UFA/SFA 1.47 " 0.24 Short/Long 0.97 " 0.05 a Total lipids (ww) 1.79 " 0.42 b Total lipids (dm) 9.25 " 1.81 b

3.77 " 0.31 4.18 " 0.72 0.37 " 0.06 0.36 " 0.05 0.10 " 0.00 0.10 " 0.00 25.23 " 1.42 ab 23.42 " 2.21 b 0.10 " 0.00 0.12 " 0.11 0.27 " 0.06 0.28 " 0.04 5.37 " 0.31 b 5.60 " 0.32 b 0.35 " 0.21 0.13 " 0.05 0.10 " 0.00 0.13 " 0.06 0.10 " 0.00 0.10 " 0.00

3.90 " 0.17 0.33 " 0.06 0.10 " 0.00 23.60 " 1.78 b 0.15 " 0.21 0.27 " 0.06 5.50 " 0.44 b 0.10 " 0.00 0.10 " 0.00 0.10 " 0.00

0.10 " 0.00 0.13 " 0.06 5.20 " 0.92 b 0.23 " 0.06 15.40 " 2.35 b 2.87 " 0.31 2.67 " 0.32 1.33 " 0.55 b 0.63 " 0.29

0.13 " 0.05 0.13 " 0.06 7.00 " 0.89 a 0.26 " 0.09 21.28 " 1.74 a 2.96 " 0.44 2.78 " 1.53 2.88 " 0.82 a 0.38 " 0.19

0.10 " 0.00 0.10 " 0.00 7.47 " 0.38 a 0.23 " 0.12 22.60 " 1.81 a 3.27 " 0.31 2.23 " 1.76 2.47 " 0.23 ab 0.25 " 0.21

0.80 " 0.17 0.67 " 0.06 0.10 " 0.00 0.60 " 0.10 4.63 " 0.64 a 0.27 " 0.06 1.30 " 0.17 18.50 " 3.94

0.80 " 0.07 0.78 " 0.04 0.33 " 0.40 0.60 " 0.17 3.50 " 0.23 b 0.26 " 0.05 1.27 " 0.31 12.02 " 2.01

0.80 " 0.10 0.77 " 0.06 0.45 " 0.49 0.53 " 0.06 3.67 " 0.29 ab 0.23 " 0.06 1.20 " 0.00 11.83 " 1.96

6.53 " 0.55 ab 0.10 " 0.00 0.60 " 0.17 0.40 " 0.00 0.97 " 0.06 0.10 " 0.00 0.33 " 0.06 35.60 " 1.65 28.53 " 4.50 b 35.87 " 4.91 26.87 " 4.94 9.00 " 0.36 3.00 " 0.61 1.81 " 0.13 0.95 " 0.06 ab 3.71 " 1.93 a 14.23 " 5.28 ab

6.90 " 0.25 a 0.12 " 0.04 0.60 " 0.12 0.32 " 0.08 0.65 " 0.06 0.13 " 0.05 0.46 " 0.53 34.60 " 2.62 37.66 " 0.88 a 28.04 " 2.78 19.02 " 2.61 9.02 " 0.22 2.12 " 0.25 1.93 " 0.22 0.80 " 0.10 b 3.82 " 0.14 a 17.00 " 1.15 a

6.90 " 0.26 a 0.13 " 0.06 0.53 " 0.06 0.27 " 0.06 0.65 " 0.07 0.10 " 0.00 0.60 " 0.69 33.93 " 2.15 38.60 " 1.15 a 27.47 " 2.80 18.53 " 2.67 8.93 " 0.25 2.10 " 0.26 1.95 " 0.18 0.79 " 0.04 b 4.08 " 0.63 a 17.14 " 3.61 a

Means in the same row with different letters are significantly different (P v 0.05)


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satiety feeding rate. The treatment 1.2% give the highest short-long chain ratio. These states can be justified by the fact that with the increase in feeding level there is a subsequent increase of the growth rate and during their growth the animals build more tissues and need more plasmatic membranes and therefore more long chain fatty acids with a high unsaturation. The results obtained show that the effect of feeding level applied during the on-growing cycle concern mainly the productive traits. These results are in agreement with Zoccarato et al.24 The highest feeding rate promotes a bigger quantity of fat reserve not only in the intramuscular area but also in the perivisceral area. The consumer is penalised by the lower dressing percentage. The small number of significant differences for the fatty acid profile confirms that the deposit sites are regulated by some genetic control mechanism. The fulfilling of essential fatty acid requirements prevent the apparition of modification on muscular lipid fraction. In order to observe an alteration in the profile of fatty acids in rainbow trout, it is necessary to turn to a fat source different from fish25,26 or to supplement the diet with a lipid source enriched with specific fatty acids as oleic.27 The values of indexes relating to dietetic factors linked with coronary diseases are reported in Table 6. Atherogenetic indexes are lower than those reported by Ulbricht and Southgate11 for lamb (1.00) and bovine meat (0.72), very similar to those reported for lean pork (0.60) and for margarine (0.50) and higher than those of mackerel (0.28). Instead, thrombogenetic indexes are widely lower than those of products reported above: lamb (1.58), bovine meat (1.08), lean pork (1.37) with the exception of mackerel (0.16) that, being a marine fish, is high in n3 polyunsaturated fatty acids. The saturated/polyunsaturated ratio is very low compared to the products listed above, mackerel included (0.94). From the data of Ulbricht and Southgate11 it appears that meat from TABLE 6. Indexes correlated with cardiovascular disease (mean " s.d.). Feeding level 1.2% 1.4% 1.8% to satiety

IA

IT

S/P

0.78 " 0.14 0.63 " 0.05 0.62 " 0.13 0.59 " 0.05

0.40 " 0.13 0.29 " 0.07 0.36 " 0.07 0.36 " 0.06

0.67 " 0.23 0.56 " 0.05 0.51 " 0.07 0.52 " 0.06



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terrestrial animals have IT indexes higher than IA indexes while trout or mackerel, characterised by very low value for both indexes, have IT values lower than IA values. This feature indicates that fish can be considered as a food suitable for the prevention of thrombotic diseases. The increase of feeding rate induces an improvement of the indexes. This seems to be related to a decrease in the quantity of saturated fatty acids, whereas the feeding level does not modify the unsaturated level. Understanding that quality has to be looked at as a whole of dynamic characteristics that cannot be restricted solely to the chemical feature of meat, the results achieved can represent a useful support for the market of the finished product, since preservation and transformation are processes that need specific characteristics of the raw material, linked to postmortem transformations that influence the food stability. Furthermore no less important, is the foodstuff dietetic aspect. The observations suggest that it may be possible to modulate the foodstuff final characteristics especially for the lipid fraction, even if no substantial differences in terms of composition, due to the feeding level, were evident. This aspect is very interesting in relation to the final purpose of a product that can be considered as a foodstuff, able to prevent cardiovascular diseases. The adoption of particular evaluation criteria such as IA and IT indexes as well as the opportunity to operate on those indexes by accurate management of the feeding practice during the growing cycle, constitutes a very efficient and simple tool for the production of food that meets the human needs for a healthy diet. REFERENCES 1. Saroglia M, Zoccarato I, Terova-Saroglia G, Palmegiano GB, Cecchini S, Forneris G, Pugliese G. Nutritional value of farmed fish and human health. In: Enne G and Greppi GF (editors) Food and Health: Role of Animal Products, Biofutur-Elsevier, Paris, 1996;235-239. 2. Steffens W. Effects of variation in essential fatty acids in fish feed on nutritive value of freshwater fish for humans. Aquaculture 1997;151:97-119. 3. Lanari D. The effect of diet on the body composition of rainbow trout (Oncorhynchus mykiss). Riv Ital Acquacol 1991;26:81-94. 4. Storebakken T, Hung SSO, Calvert CC, Plisetskaja EM. Nutrient partitioning in rainbow trout at different feeding rates. Aquaculture 1991;96:191-203.


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