Fillet Composition Research Articles

Acidic composition of gilthead seabream fillets (Sparus aurata L.) fed with different lipid sources: preliminary evaluation

Dietary lipids play an important role in fish nutrition as a source provision of body energy and essential fatty acids (EFA) (Sargent et al., 1999). The low availability and the high exspense of fish oil could suggest the use of an alternative lipid source in aquaculture (Turchini et al., 2000). Alternative sources of PUFA are represented by vegetable oils, but their composition is not satisfactory for the requirements of the different species of rearing fishes...

Comparison of Various Animal Protein Sources for Growth, Feed Efficiency, and Body Composition of Juvenile Channel Catfish Ictalurus punctatus

AbstractA laboratory study was conducted to compare different animal protein sources in diets containing 32% protein for channel catfish Ictalurus punrtatus. The experimental diets were practical‐type diets and formulated to meet or exceed all known nutrient requirements for channel catfish. Twenty juvenile channel catfish (initial weight: 6.4 g/fish) were stocked into each of 25 110‐L flow‐through aquaria (five aquaria/treatment). Fish were fed twice daily to approximate satiation for 9 wk. Fish in each aquarium were counted and weighed collectively every 3 wk. No significant differences were observed in feed consumption, weight gain, feed efficiency, survival, percentages visceral fat and fillet yield, or proximate composition of fillets among channel catfish fed diets containing either 5% menhaden fish meal, meat and bone/blood meal, catfish by‐product meal, poultry by‐product meal, or hydrolyzed feather meal with supplemental lysine. The data indicate that these animal protein sources can be used interchangeably in diets for channel catfish without affecting fish growth, feed efficiency, or body composition.

Comparative composition and shelf-life of fillets of wild and cultured turbot ( Scophthalmus maximus ) and Atlantic halibut ( Hippoglossus hippoglossus )

Turbot and Atlantic halibut are highly valued fish species. However,very little is known about fillet shelf-life characteristics associated withboth species. Thus, fillet α-tocopherol content and proximate compositionof wild turbot (1.5 kg) and Atlantic halibut (1.1 kg)caught off the south coast of Ireland and the north-west coast of Iceland,respectively, were investigated. In addition, the susceptibility of fillets, storedunder retail conditions, to lipid oxidation and colour change was studied.Proximate composition analysis showed that turbot had significantly highermoisture (P < 0.001) and lower protein (P < 0.001) contents compared toAtlantic halibut. Atlantic halibut incorporated significantly higher (P <0.001) levels of α-tocopherol into fillets than turbot. Over 14 days ofstorage on ice, fillets from Atlantic halibut exhibited significantly lower (P =0.020) levels of lipid oxidation than those of turbot. However, malondialdehyde(MDA) concentrations were generally very low, never exceeding 0.6 μgg−1 fillet. Turbot maintained a significantly higher (P< 0.001) pH over the storage period. The lightness (L* values) offillets from both species increased over 14 days of storage, but wassignificantly higher (P < 0.001) in Atlantic halibut than in turbot. Turbotdeveloped a relatively intense yellow colour during storage (decrease in hueangle and increase in b* values), whereas this was not the case forAtlantic halibut. The results of this study demonstrate that fillets of wildAtlantic halibut stored on ice, were less prone to lipid oxidation anddiscolouration than those of wild turbot. However, quality changes in turbotwere very small showing that both fish have tremendous shelf-life capacities interms of lipid oxidation. These findings are considered in the context of knownmaterial for farmed fish.

Non-invasive measurement of fillet composition of four freshwater fish species by computer tomography

Thecrude fat and crude protein content of fillets was predicted by X-ray computertomography (CT) and determined by chemical analyses. Between 20 to 40 serialscans were taken of 48 freshwater fish and samples from the ground fillet withskin were prepared for chemical analyses. Fish species investigated were asfollows: common carp (n = 18), grass carp (n = 10), silver carp (n = 10) andpike-perch (n = 10), all collected directly from fishponds and processedimmediately. The variables of the prediction equations were taken from thedensity values of the Hounsfield scale, on a range between −90 and+150, by summing the frequencies within each interval of 10 values. Withprincipal component analysis fillet fat and crude protein content could beestimated with R2 = 0.88 and R2 = 0.87 accuracy,respectively. Three dimensional"volumetric" estimation of fat tissue was also carried out on the basis of fatindices developed at our lab. The fillet composition of the Cyprinid speciescould be evaluated well with the applied methods, but not that of pike-perchwhich had an extremely low fillet and body fat content.

Effect of Dietary Protein Concentration on Growth and Processing Yield of Channel Catfish, Ictalurus punctatus Raised from Advanced Fingerlings to Large Marketable Size

This study evaluated the effects of dietary protein concentration (26, 28, and 32%) and an all-plant protein diet (28% protein) on growth, feed efficiency, processing yield, and body composition of channel catfish, Ictalurus punctatus raised from advanced fingerlings to large marketable size (about 800 to 900 g/fish) for two growing seasons. Fingerling channel catfish (average weight = 56 g/fish) were stocked into twenty 0.04-ha ponds at a density of 18,525 fish/ha. Fish were fed once daily to satiation during the two growing seasons and fed according to recommended winter feeding schedules during the winter. There were no differences in diet consumption, weight gain, feed conversion ratio, survival, processing yields (carcass, shank fillet, and nugget), or fillet composition (moisture, protein, fat, and ash) among fish fed the various diets. These results indicate that a 26% protein diet containing plant and animal proteins or a 28% all-plant protein diet is adequate for channel catfish raised in ponds from advanced fingerlings to large marketable size without adversely affecting weight gain, feed efficiency, processing yield, or body composition. Large marketable-size channel catfish appear to use diets less efficiently but give higher processing yields compared to small marketable-size fish.

Growth, feed utilisation, carcass composition and sensory characteristics of rainbow trout treated with recombinant bovine placental lactogen and growth hormone

The effect of treating rainbow trout (initial weight=51 g, T=10–11.5°C, fed to satiation), with recombinant bovine placental lactogen (PL, 2 μg g −1 body weight week −1) or growth hormone (GH, 2 μg g −1 body weight week −1), upon growth, feed conversion, sensory characteristics and fillet composition was investigated, with reference to three control groups. Hormone treatments were given for a period of 5–6 weeks, followed by a period of 13 weeks during which animals were left undisturbed. Differences in proximate composition of carcass ( P<0.0005) and entrails ( P<0.01), but not skeleton, were observed when sampled fish (PL at 5 weeks, GH at 6 weeks, and control at 7 weeks) of similar length were compared. At trial termination, eight animals from each group were randomly caught and slaughtered. The left fillet of each fish was skinned, vacuum-packed and boiled for 5 min, while the right fillet was used for compositional analyses. A trained sensory panel for flavour, odour, texture and appearance examined boiled fillets. PL-treated fish were deemed to express superior characteristics to control or GH-treated trout, particularly for juiciness ( P<0.05). GH-treated animals received lower scores ( P<0.05) for both sweet odour and flavour. Concurrent with a higher score for dryness, GH-treated fish returned higher fillet protein content ( P<0.05) than other groups.

Evaluation of Bioelectric Impedance to Predict Carcass Yield, Carcass Composition, and Fillet Composition in Farm‐Raised Catfish

Abstract.— Bioelectric impedance analysis (BIA) was evaluated as a method for predicting carcass yield, fat, and moisture in live channel catfish, Ictalurus punctatus (N = 20), and fat and moisture in fillets from channel catfish (N= 20) and channel catfish female × blue catfish male, I. furcatus, hybrids (N= 20). Fish were cultured in ponds, fed a commercial catfish diet (28% protein), and harvested at market weight (450 g‐900 g, ∼19 months post‐hatch). Live channel catfish were tranquilized, weighed, and sexed. Resistance and reactance were measured with a four‐terminal impedance analyzer. Fish were then deheaded, eviscerated, weighed, and carcass yield was calculated. Fillets from channel catfish and channel catfish × blue catfish hybrids were measured for weight, resistance, and reactance. Carcasses and fillets were ground and fat and moisture were determined by chemical analysis. Regression models including total weight, resistance, and reactance as independent variables explained 71%, 75%, and 65% of the variation in carcass yield, fat, and moisture, respectively, in live fish. Regression models with fillet weight, resistance, and reactance as independent variables explained 62% and 41% of the variation in fillet fat and moisture, respectively, in channel catfish, and 53% and 58% of the variation in fillet fat and moisture, respectively, in channel catfish × blue catfish hybrids. Models including resistance and reactance explained significantly more variation in the traits measured than did models containing only whole weight as an independent variable. Improvements in prediction accuracy will be needed to make BIA a useful tool for predicting carcass yield, carcass composition, and fillet composition in farm‐raised catfish.

Effects of altered ration levels on sensory characteristics, lipid content and fatty acid composition of rainbow trout ( Oncorhynchus mykiss)

This study describes the effects of altered ration levels on sensory characteristics, lipid content and fatty acid composition of rainbow trout fillet. Ration levels were altered from adequate to restricted level after 0.2 and 1.0 years from hatching and from strongly restricted and restricted levels to adequate level 1.0 years from hatching. A selected and trained panel carried out descriptive sensory tests on fish fillet cross-sections. The intensity of total odour increased, and that of juiciness decreased with age, independent of ration level. Ration level had an overall effect on the total taste intensity, independent of age. Fresh odour correlated negatively to the saturated fatty acids 14:0 ( r=−0.834; p<0.001), 16:0 ( r=−0.831; p<0.001) and 18:0 ( r=−0.668; p<0.05). Trout that had their ration level altered from restricted to adequate level 1.0 years after hatching had a higher lipid content than trout having their ration level altered from adequate to restricted level after 0.2 and 1.0 years, respectively. Including fillet lipid content in the statistical model indicated that lipid is an important factor decisive for total taste and flesh texture of the trout. Fish having their ration level altered from adequate to restricted level after 0.2 years had a significantly lower condition factor than fish having it altered 1.0 years after hatching.

Ingestion of repeatedly heated edible oil activates phospholipase A2 and protein kinase C in rat liver, kidney and colonic mucosa

An improved gas chromatography method for the simultaneous separation of 52 fatty acids (FAs) has been developed. For both oleic acid and linoleic acid, a good resolution was achieved for their positional and geometrical (cis/trans) isomers. This method was validated to be precise, accurate and sensitive. With this method, the FAs profiles in palm oil and chicken fillets were analyzed. In general, small changes were observed in the composition of FAs and formation of trans isomers after 8 h frying at the temperature lower than 200 °C. However, with extreme deep-frying process, the thermal degradation and TFAs formation in frying oil increased in direct proportion to frying temperature and time. Moreover, the FAs composition of fried chicken fillets was found to be mostly in correspondence with that of the frying oil, which might be due to the oil absorption or interaction between the frying oils and frying materials.

Influence of the addition of antioxidants in vivo on the fatty acid composition of fish fillets

In this study, the influence of the addition of antioxidants in vivo on the fatty acid composition of the flesh of a freshwater fish known as “pacu” ( Piaractus mesopotamicus) is verified. Four groups (one being the control group) of juvenile “pacu” were cultured on isocaloric and isoproteic diets. The lipid source was soybean oil and diets were added with either 100 ppm of α-tocopheryl acetate, or 100 ppm of BHT or 1.4 g of rosemary extract (Herbalox ®)/kg diet. The fatty acid composition of the lipids of the different groups was determined before and after irradiation at 2 and 3 kGy, respectively, for the evaluation of the protective effects of the different antioxidants. Similarly, thiobarbituric acid reactive substances (TBARS) were determined from irradiated and nonirradiated samples. The results showed that the use of antioxidants altered the fatty acid composition of the fillets. TBARS and irradiation confirmed their important role in protecting against lipid oxidation. Among all the antioxidants used, tocopherol was the most efficient, as shown by the highest percentage of polyunsaturated fatty acids (PUFA), by the lowest values of TBARS and by the analyses of the individual fatty acid levels at different irradiation doses. Significant statistical differences were observed only in 17% of the fatty acids in the fillets of the groups.

Effect of Dietary Protein Concentration and Feeding Rate on Weight Gain, Feed Efficiency, and Body Composition of Pond‐Raised Channel Catfish Ictalurus punctatus1

AbstractTwo experiments were conducted in earthen ponds to evaluate the effect of dietary protein concentration and feeding rate on weight gain, feed efficiency, and body composition of channel catfish. In Experiment 1, two dietary protein concentrations (28% or 32%) and four feeding rates (≤ 90. ≤ 112, ≤ 135 kg/ha per d, or satiation) were used in a factorial arrangement. Channel catfish Ictalurus punctatus fingerlings (average size: 27 g/fish) were stocked into 0.04‐ha ponds at a rate of 24,700 fish/ha. Fish were fed once daily at the predetermined maximum feeding rates for 282 d (two growing seasons). In Experiment 2, three dietary protein concentrations (24, 28, or 32%) and two feeding rates (≤ 135 kg/ha per d or satiation) were used. Channel catfish (average size: 373 g/fish) were stocked into 0.04‐ha ponds at a rate of 17,300 fish/ha. Fish were fed once daily for 155 d. In both experiments, five ponds were used for each dietary treatment. Results from Experiment 1 showed no differences in total feed fed, feed consumption per fish, weight gain, feed conversion ratio (FCR), or survival between fish fed diets containing 28% and 32% protein diets. As maximum feeding rate increased, total feed fed, feed consumption per fish, and weight gain increased. There were no differences in total feed fed, feed consumption per fish, or weight gain between fish fed at ≤ 135 kg/ha per d and those fed to satiation. Fish fed the 28% protein diet had a lower percentage carcass dressout and higher percentage visceral fat than fish fed the 32% protein diet. Dietary protein concentrations of 28% or 32% had no effect on fillet protein, fat, moisture, and ash. Feeding rate did not affect FCR, survival, percentage carcass dressout, or fillet composition, except fillet fat. As feeding rate increased, percentage visceral fat increased. Fish fed at ≤ 90 kg/ha per d had a lower percentage fillet fat than fish fed at higher feeding rates. In Experiment 2, dietary protein concentration or maximum feeding rate did not affect total feed fed, feed consumption per fish, weight gain, FCR, or survival of channel catfish. Feeding rate had no effect on percentage carcass dressout and visceral fat, or fillet composition. This was due to the similar feed consumption by the fish fed at the two feeding rates. Fish fed the 24% protein diet had lower carcass dressout, higher visceral fat and fillet fat than those fed the 28% or 32% protein diet. Results from the present study indicate that both 28% and 32% protein diets provide satisfactory fish production, dressed yield, and body composition characteristics for pond‐raised channel catfish fed a maximum rate of 90 kg/ha per d or ahove.

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 3×2 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.

Evaluation of Practical Diets with Various Levels of Dietary Protein and Animal Protein for Pond‐Raised Channel Catfish Ictalurus punctatus1

AbstractThree levels of dietary protein (26, 28, or 32%) and four levels of animal protein (0, 2, 4, or 6%) were evaluated in a factorial experiment for pond‐raised channel caffish using practical‐type extruded feeds. Meat, bone, and blood meal (65% protein) was used as the animal protein source. Channel catfish fingerlings (average weight: 69 glfish) were stocked into 48 0.04‐ha ponds at a rate of 24,700 fishha. Four ponds were used for each dietary treatment. Fish were fed once daily to apparent satiation for 158 d. No differences were observed in weight gain, feed consumption, feed conversion ratio, survival, and hematocrits of channel catfish fed diets containing various levels of dietary protein and animal protein. Inclusion of animal protein in the diet did not affect fish dressout, percentage visceral fat, or fillet composition. Comparison of means pooled by dietary protein without regard to animal protein showed that fish fed diets containing 26% protein had a lower percentage dressout than fish fed higher protein diets (55.4% vs. 56.3%). Fish fed the 32% protein diet had lower visceral fat than those fed the 26% or 28% protein diet (2.9% vs. 3.6% or 3.4%). Fillet fat was lower for fish fed the 32% protein diet than for fish fed the 26% protein diet (5.8% vs. 7.1%). Fillet fat in fish fed the 28% protein diet (6.5%) was not different from fish fed either 26% or 32% dietary protein. No differences were detected in fillet protein, moisture, and ash concentrations among fish fed diets containing various concentrations of protein. There were no interactions between dietary protein and animal protein for any variables. Results from the present study indicate that animal protein can be eliminated from diets for grow out of channel catfish fed to apparent satiation using diets containing 26% to 32% crude protein.

EFFECT OF SMOKE SOURCES ON QUALITY AND STORAGE STABILITY OF CATFISH FILLET (Clarias macrocephatus Gunther)

ABSTRACTThe effect of smoke sources, bagasse and coconut husk, on the chemical composition, acceptability and quality changes of catfish fillets was investigated. Catfish smoked with either of the sources had similar compositions. Catfish fillets smoked with coconut husk attained significantly higher preference scores for color but odor scores were lower compared with those smoked with bagasse (p &lt; 0.05). However, no significant differences in other attributes were observed for fillets smoked by the two different kinds of starting material. Smoked fillets showed lower TBA values, ammonia content, aerobic plant count (APC), yeast and mold than the control throughout 10 weeks of storage at 4C. For the smoked fillets, nonenzymatic browning was prevalent.

Starvation prior to slaughter in Atlantic salmon ( Salmo salar) : II. White muscle composition and evaluation of freshness, texture and colour characteristics in raw and cooked fillets

Muscle composition and quality characteristics of fillets were investigated in triplicate groups of 5-kg Atlantic salmon starved at low water temperatures for 0, 3, 7, 14, 30, 58 or 86 days prior to slaughter. White muscle and raw fillets were analysed at slaughter and after 4 and 12 days of ice-storage of gutted fish, whereas sensory analyses of cooked fillets were performed after storage for 13–16 days. At slaughter, the level of glycogen in white muscle decreased with the length of starvation. After 4 and 12 days of ice-storage, lactate and glycogen levels decreased and pH increased in white muscle with increasing starvation time. The K-value, determined after 4 and 12 days of ice-storage, decreased as the duration of starvation increased. Trimethylamine was not detected in white muscle. Sensory analyses showed that cooked fillets from groups starved for 86 days had less fresh flavour than that of groups starved for 30 days or less. The fillets of groups starved for 30 days had significantly higher acidulous flavour compared with that of groups starved for 0–14 days, whereas groups starved for 58 or 86 days had significantly less acidulous flavour than all other groups. The sensory assessed hardness of cooked fillets was significantly lower in groups starved for 86 days vs. those starved for 0, 14 or 30 days. In contrast, instrumental texture analyses of raw fillets, after 4 days of ice-storage, showed that the force against compression (at 5 mm) was higher in groups starved for 58 or 86 days than in those starved for a shorter time. Although astaxanthin concentration was not significantly affected by starvation time, instrumental colour analyses (CIE 1976) of raw fillets revealed changes in lightness ( L*) and yellowness ( b*). Although starvation produced some changes in white muscle composition, the rather marginal differences in freshness, texture and colour characteristics of raw or cooked fillets when starvation time varied from 0 to 86 days, suggest that starvation is a rather weak tool for changing fillet quality in Atlantic salmon.

Growth, feed conversion, fillet proximate composition and resistance to Edwardsiella ictaluri of channel catfish, Ictalurus punctatus (Rafinesque), blue catfish, Ictalurus furcatus (Lesueur), and their reciprocal F1 hybrids fed 25% and 45% protein diets

Juvenile channel catfish, Ictalurus punctatus (Rafinesque), blue catfish, I. furcatus (Lesueur), and their reciprocal Fl hybrids were fed practical diets containing 25% and 45% protein during a 10-week trial to determine the effects of genotype, dietary protein level and genotype X diet interactions on growth, feed conversion ratio (FCR), fillet proximate composition and resistance to the bacterium Edwardsiella ictaluri. Rankings of genotypes (best to worst) for absolute weight gain, percentage weight gain and FCR were: channel, channel female X blue male, blue, and blue female X channel male for the 25% protein diet; and channel, channel X blue, blue X channel, and blue for the 45% diet. Diet did not affect growth or FCR of channel catfish, but growth and FCR were better for blue catfish and both hybrids fed the 25% diet compared to those fed the 45% diet. Channel catfish additive genetic and maternal effects were favourable, and heterosis was negative for growth and FCR. After adjusting for effects of fish size, genotype had no effect on fillet composition. Fillet protein was higher for all genotypes, and fillet lipid was lower for blue catfish and hybrids fed the 45% diet than for fish fed the 25% diet. Genotype X diet interactions observed for growth, FCR and fillet lipid appeared to be a result of poor palatability of the 45% diet to blue catfish and hybrids. Survival (76-93%) and antibody levels (0.10-0.24 OD) after exposure to E. ictaluri at the end of the feeding trial were not affected by genotype or diet. Hybridization of blue catfish and channel catfish would not be an effective method for improving the traits measured for the fish strains and diets used in this study.

Effects of supplemental lysine and methionine in low protein diets on weight gain and body composition of young channel catfish Ictalurus punctatus

Two experiments were conducted to evaluate the effects of supplementation with lysine, methionine, or both in low protein but amino acid (AA)-replete diets on weight gain and body composition of channel catfish (mean initial weight: 10–11.9 g/fish) raised under laboratory conditions. In experiment 1, a 2×3 factorial arrangement with two feeding rates (approximately 75 and 100% satiation) and three test diets was used. Diets 1 and 2 were formulated to contain 32 and 24% crude protein, respectively. Diet 3 was the same as diet 2 except that 0.4% supplemental lysine was added. Fish were fed once daily for 12 weeks. In experiment 2, a 2×4 factorial arrangement with two dietary protein levels (24 or 28%) and four AA supplements was used. Lysine, methionine, or both were supplemented to the basal diets to bring the level of these two essential AAs to 30% above the requirement for channel catfish. Fish were fed once daily to approximate satiation for 12 weeks. In both experiments, five aquaria were used in each dietary treatment. In experiment 1, regardless of feeding rate, fish fed diets containing 24% protein with or without supplemental lysine gained less weight and converted feed less efficiently than fish fed the 32% protein diet. There were no differences in weight gain between fish fed the 24% protein diets with and without supplemental lysine. Feed efficiency of fish fed the 24% protein diet with supplemental lysine was higher than that of fish fed the diet without supplemental lysine. Fillet fat of fish fed diets containing 24% protein with or without supplemental lysine was greater than that of fish fed the 32% protein diet. There were no differences in fillet fat between fish fed the 24% protein diets with and without supplemental lysine. Fillet protein was not affected by diet or feeding rate. In experiment 2, regardless of dietary protein concentration, no significant differences were observed in weight gain, feed consumption, feed efficiency, or fillet composition among fish fed diets with or without supplemental AAs. Results from this study indicate that supplementation with lysine and/or methionine in low protein but AA-replete diets is not beneficial for channel catfish.

Relationships between carotenoid concentration and colour of fillets of Arctic chair,Salvelinus alpinus(L.), fed astaxanthin

The relationships between fillet colour (CIE L* a* b* and CIE L* C* H°ab) and carotenoid concentration were investigated using samples taken from Arctic charr, Salvelinus alpinus (L.), of different ages and sizes, which were held under a variety of rearing conditions. Relationships between colour parameters and carotenoid concentrations were nonlinear. Increasing carotenoid concentrations led to increased redness (a*), yellowness (b*) and chroma (C*), and decreased lightness (L*) and hue angle (H°ab). Redness was the colour parameter most highly correlated with carotenoid concentration of the Arctic charr fillets. For a given redness value, yellowness was higher in sexually mature than in immature Arctic charr. This was possibly a result of mature fish having higher proportions of idoxanthin in the fillet than immatures. Alternatively, the differences in yellowness may have been a consequence of differences in proximate composition of fillets of mature and immature charr. There were also differences in yellowness in fillets from Svalbard and Hammerfest charr, Svalbard fish having the most yellow fillets. Fish from the two strains did not differ in relative proportions of fillet carotenoids, indicating that differences in colour were mediated through differences in other chemical properties.

Effects of dietary levels of 20:5n-3 and 22:6n-3 on tissue lipid composition in juvenile Atlantic salmon, Salmo salar , with emphasis on brain and eye

Four dietary groups of juvenile Atlantic salmon, Salmo salar L., each with three replicates, were fed diets with increasing levels of docosahexaenoic acid (22:6n‐3; DHA) and eicosapentaenoic acid (20:5n‐3; EPA). Fatty acid composition of brain and eye was determined at the start and approximately every 3 weeks during the experimental period, and fatty acid composition of liver and fillet was determined in fish from the final sampling. Lipid class composition of brain and eye, and fatty acid composition of these lipid classes was determined at the end of the experiment. There was no effect of increasing dietary DHA content on fatty acid composition, lipid class composition or DHA levels in the lipid classes in the juvenile Atlantic salmon brain. The increasing dietary EPA content, however, was reflected in both the total fatty acid composition and in the EPA content in neutral lipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). A minor effect of the increasing dietary DHA content was found in the lipid composition of the juvenile salmon eye. Both EPA and 18:2n‐6 levels in eye, however, clearly reflected the increasing and decreasing, respectively, dietary levels of these two fatty acids. The dietary EPA levels also affected the EPA levels in neutral lipids, PC, PE, PI and PS (phosphatidylserine) in the juvenile salmon eye. The results demonstrate that these dietary levels of DHA had no effect on brain lipid composition and only a minor effect on eye lipid composition. Furthermore, the dietary EPA levels significantly affected the lipid composition of both brain and eye. The fillet fatty acid composition reflected the dietary fatty acid composition, except for the DHA/EPA ratio, which was reversed in fillet compared with that in the diets. The liver fatty acid composition was also affected by the increasing dietary EPA and DHA levels.

Influence of fish meal quality and feed pellet on growth, feed efficiency and muscle composition in gilthead seabream ( sparus aurata)

The effect of fish meal quality on growth, feed efficiency, protein digestibility and fillet composition was studied in a growth experiment with gilthead seabream. The experiment included a comparison of pelleted feed with extruded feed. The fish were fed three extruded diets which varied in the quality of the fish meal used in the respective feeds: low quality fish meal, good quality fish meal, and a mixture (50%) of the two fish meal qualities. Fish meal quality was judged by protein digestibility as measured with mink as the test animal and by the content of biogenic amines. A fourth experimental group was fed a pelleted feed with the same mixed fish meal blend. The experiment started with 70 g seabream and lasted for 3 months until the fish reached about 160 g. All groups showed good growth and feed efficiency during the experimental period, with daily specific growth rates (SGR) of 0.90–1.00% and feed efficiencies (FE; fish weight gain per feed offered) from 0.58 to 0.66. The fish fed the feed with low quality fish meal showed significantly poorer feed efficiency than the other groups, and there was a significant correlation between feed efficiency obtained in seabream and the protein digestibility as measured with mink. No difference was observed among groups fed the extruded diets, for growth, fillet composition or amount of liver or viscera, although a significant correlation was obtained between SGR and protein digestibility in mink. Fillet lipid content was higher in fish fed the extruded feed, compared with those fed the corresponding pelleted diet. Protein digestibilty in seabream showed no difference among the extruded feeds, while the pelleted feed was significantly lower.