Ragnar Nortvedt

Body composition and sensory assessment of three weight groups of Atlantic halibut (Hippoglossus hippoglossus) fed three pellet sizes and three dietary fat levels

Abstract In the present investigation, we tested the effects of varying initial fish weight (0.8 to 1.8 kg), pellet size (12–27 mm Φ), dietary fat level (10–39% of dry matter) and their cross-terms upon the fat content in a standardized fillet cut of farmed Atlantic halibut (1.3–2.7 kg) after 6 months. A factorial design (FD, 2 3 ) plus four centre points was applied. The fish were individually tagged and reared at a mean temperature of 8.2°C. Lipid content in the fillet was modelled with the aid of PLS (partial least squares) regression on size and sex subgroups. A sensory panel consisting of 11 trained assessors tested the effects of final fish weight and dietary fat contents on multiple sensory parameters. These data were analysed by ANOVA and principal component analysis (PCA). Wide intra- and interindividual variation in fat content were observed. A standard Atlantic halibut fillet quality cut (A) is suggested for future work on fillet quality, together with measurements of fat along the dorsal and the ventral fin base. The PLS models of lipid deposition in the fillets showed a positive influence from increased initial fish weight and increased dietary fat content. Pellet size showed a minor positive contribution to the fat deposition in the fillet. The sensory test showed that larger halibut (2.1–2.7 kg) fed diets containing 20 or 39% fat were characterized by a fresher and more acidic flavour and a more juicy consistency, compared to smaller fish (1.4 kg), irrespective of the small fish groups dietary regime. The smaller fish were characterized by rancid flavour and off-flavour. In addition to the sensory data, the evaluation of the feed from a feed production viewpoint showed that it is more economical to utilize herring filleting offal to produce a high fat feed (39%) that ensures the same fillet quality in the Atlantic halibut as the medium fat feed does. We, thus, conclude that the fat content in the feed for Atlantic halibut should be optimized at a level near 40% in due time before the slaughtering period, and that the fish preferably should pass 2.0 kg before being slaughtered.

Studies on the nitrogen recovery in enzymic hydrolysis of Atlantic salmon (Salmo salar, L.) frames by Protamex™ protease

In three consecutive experiments, frames without heads from Atlantic salmon were hydrolysed by Protamex™ protease. In experiment I (2 4 factorial design) nitrogen recoveries (NR) of 44–76% were obtained, after 120 min of hydrolysis, by systematically varying the hydrolysing parameters, starting pH (5.4–7.7), temperature (36–50 °C), E:S ratio (30–90 AU kg −1 crude protein) and frames–water ratio (0.71–1.21) between low and high levels. The highest levels of E:S ratio (90 AU kg − 1 crude protein), temperature (50 °C) and starting pH (7.7) and the lowest level of frames–water ratio (0.71) resulted in the highest NR (76%). In experiment II, the optimal temperature and starting pH in the hydrolysis with Protamex™ were established at 50–56 °C and 6.5–7.6, respectively. Beyond these temperature and starting pH intervals, the NR tended to decrease. In experiment III, at optimal temperature (50 °C) and starting pH (6.5) conditions and frames–water ratio of 1.2, NR of 43–61% were achieved after 60 min of hydrolysis, by varying the E:S ratios from 10–90 AU kg − 1 crude protein. The highest E:S ratio resulted in the highest NR but running the hydrolysis for a period longer than 60 min resulted in little increase in NR.

Macronutrient composition of formulated diets for Atlantic halibut (Hippoglossus hippoglossus, L.) juveniles

Abstract A three component mixture design was used to investigate the optimum composition of macronutrients for Atlantic halibut juveniles (0.5 g startweight). Protein, lipid and carbohydrate were varied between 530–830, 50–300 and 0–150 g kg−1 dry wt., respectively. Of the 21 diets, 20 produced were fed to fish in single tanks, while 1 diet was fed to fish in four replicate tanks to estimate inter-tank variation. The experiment lasted for 2 months. Carbohydrate levels above 50 g kg−1 were suboptimal for the halibut as seen from lowered specific growth rates (SGR), increased hepatosomatic indices and accumulation of carbohydrate in the liver. At low carbohydrate levels (0 and 50 g kg−1), the specific growth rates appeared similar with lipid levels between 50 and 250 g kg−1, while 300 g lipid kg−1 resulted in growth depression. At higher carbohydrate levels, fish growth was reduced with lipid levels increasing above 100 g kg−1. It can be concluded that Atlantic halibut juveniles have low tolerance to dietary carbohydrate, whereas dietary lipid can be varied over a wide range without affecting growth performance. Based on the limits of 50 g kg−1 for carbohydrate and 250 g kg−1 for lipids, the protein requirement appears to be at least 630 g kg−1.

Atlantic salmon (Salmo salar, L) as raw material for the smoking industry. II: Effect of different smoking methods on losses of nutrients and on the oxidation of lipids

The changes in total fat content, fatty acid composition, tocopherol, ascorbic acid, pH and oxidation were analysed in Atlantic salmon (Salmo salar, L.) in response to either cold smoking (20 or 30 C) or electrostatic smoking. Both fresh and frozen fillets were dry-salted before smoking. The fish smoked were the lean ocean-ranched salmon caught off Iceland in June 1998 and farmed Norwegian salmon, slaughtered in either November 1998 or April 1999, differing in fresh fillet fat content from 84 to 169 g.kg 1 wet weight. The fresh material used in smoking significantly affected the smoking loss of nutritive components in the fillets. The leaner the fish the higher percentile loss in fillet fat. Ascorbic acid decreased about 80 percent from the fresh value, independent of smoking temperature (20 or 30 C). The fish that were dry-salted and electrostatically smoked only lost about 10 percent of the fresh ascorbic acid content, independent of the type of raw material used, indicating a conserving effect on ascorbic acid by the electrostatic process. Also, the electrostatically smoked fish showed a smaller drop in fillet pH than cold-smoked fillets, while tocopherol was little affected by the smoking methods tested. # 2002 Elsevier Science Ltd. All rights reserved.

Atlantic salmon (Salmo salar, L.) as raw material for the smoking industry. I: effect of different salting methods on the oxidation of lipids

Abstract The changes in total fat content, fatty acid composition, tocopherol, ascorbic acid, pH and oxidation were analysed in response to different salting methods, either dry or brine, in cold-smoked (20 or 30xa0°C) Atlantic salmon ( Salmo salar , L.). The fish were lean ocean-ranched salmon caught at Iceland in June 1998 and farmed Norwegian salmon slaughtered in November 1998 and April 1999, differing in fresh fillet fat content from 84 to 169 g kg −1 wet weight. The total fat content decreased in all groups during processing, whereas the relative fatty acid composition of the fillets was not severely affected during salting and cold-smoking. The most conspicuous process consumption of antioxidants in all the groups was the relative ascorbic acid loss (58–82%). Generally, no clear effect of different salting methods was observed on the tocopherol loss during processing, but brine salting had a stronger effect on both fat and ascorbic acid loss than dry salting. The fattiest fish showed the highest oxidation during processing and they lost more tocopherol, but the final oxidation levels were generally low (thiobarbituric acid reactive substances, TBARS: 6.0–14.7 μmol kg −1 ), reflecting the antioxidative protection offered by the vitamins during processing.

Dissolved organic carbon associated with sinking can be crucial for estimates of vertical carbon flux

Abstract Sinking particles are a major vehicle of carbon export from surface waters of the ocean and thus their rates of sedimentation are important for assessing the role of the ocean for the sequestration of atmospheric carbon dioxide. Oceanographers often use sediment traps to estimate particle sedimentation. We suggest thar the downward transport of carbon via particles may be underestimated, as dissolved organic carbon (DOC) released from trapped particles is not usually considered, thus hindering attempts to “balance” the carbon budget Latent variable analyses of trap data enabled us to more accurately estimate flux of particulate carbon. In particular, we present a method to separate the fraction of DOC leached from zooplanktonic swimmers ti-om DOC originating from sedimented particles. The latter we tenn particle-associated DOC (pDOC). The precise impact of this process in different ecosystems may vary. Thus, an application of the statistical procedure should be made for individual sets of sedimen...

Application of near-infrared transmittance spectroscopy in the determination of fat, protein and dry matter in Atlantic halibut fillet

Near infrared transmittance (NIT) spectroscopy (850–1048 nm) has been applied to the measurement of fat, protein and dry matter in wet homogenized Atlantic halibut (Hippoglossus hippoglossus) fillet. A total of 155 fillet cuts (five sample sites) were selected from the start of the investigation (survey I) and 98 fillet cuts (one sample site) were also selected from eight fish groups six months later (survey II). The fish groups originated from a slaughtering quality experiment, where fish size and fat content in the feed had been varied. The multivariate calibration models were tested separately for each survey and after mixing the survey samples. The models were also tested after inclusion of sample temperature or fish weight, or after reduction to spectra of eight wavelengths. The selected fillet cuts from survey II gave calibration models with the best prediction abilities for fat and dry matter, whereas the combination of samples from both surveys gave the best prediction abilities for protein. The constituent ranges (w.w.) were: 10–123 g/kg fat, 165–274 g/kg protein and 234–335 g/kg dry matter. The partial least squares regression resulted in the following prediction errors, expressed as root-mean-square error of cross validation: 2.7 g/kg fat, 5.2 g/kg protein and 4.2 g/kg dry matter. The temperature adjustment had positive influence on the test set validation of protein and dry matter, whereas the fish-weight adjustment had positive influence on the test set validation of fat. Calibration models based on eight wavelengths were not optimal, but showed promising results, applicable in a simpler instrument for future online quality monitoring of Atlantic halibut fillet.

Multivariate evaluation of feed for Atlantic halibut

Abstract The present investigation tested three physical properties of fish feed: dry matter content, floating vs. sinking feed, pellet size and their cross-terms upon growth and feed utilization of Atlantic halibut ( Hippoglossus hippoglossus ) in the ongrowing phase. A factorial design (FD, 2 3 ) with four center points was applied. Each of three size subgroups within each rearing tank were modeled across 12 tanks. Nine single growth and feed utilization responses and three combined responses (super Y s) were modeled with the aid of PLS (partial least squares regression). The fish were individually tagged and reared for three months at a mean temperature of 8.7°C. The models of growth and feed utilization were improved by sorting the individual fish, according to blindness, and by splitting the modeling in size and time groups. The application of weighted multiresponse models gave more relevant information than single response models. High dry matter content (dry feed) caused the most unambiguous and positive effect on growth and feed utilization. The floating property of the feed was negatively correlated to growth rates, especially for small fish. The pellet size of 8–9 mm was too big for the small fish ( Y response. Future feeds should consequently maximize these parameters within biological reasonable limits to achieve the best utilization of the feed.

Multivariate approach to the study of fish growth

Abstract Atlantic salmon parr (Salmo salar) were reared in tanks under six controlled environmental combinations of oxygen saturation (54–120%), water flow (3–22 1 min −1 ) and biomass (22–64 kg m −3 ). Growth and water quality were monitored over seven months until parr—smolt transformation. Data were interpreted by partial least squares (PLS) regression in the SIRIUS program. Loadings from the PLS analysis revealed that the three controlled factors investigated and their cross terms covaried positively with specific growth rate (SGR). Salmon in one of the tanks (F) were studied more intensively to reveal the significance of 28 environmental parameters on SGR. Loadings from this PLS analysis showed that reduction in number of fish, due to control of biomass, specific flow rate (1 kg −1 min −1 ) and specific oxygen consumption (mg kg −1 min −1 ) had the most positive influence on SGR in tank F. Daily variation in salinity seemed to be negatively correlated with SGR. The multivariate approach has consequently proved to be useful for interpretation of fish growth. The present investigation serves as an example of post-treatment of an undesigned experiment, and points to possible ways to improve aquaculture research. Economic aspects are discussed in terms of the researchers gain and the farmers outcome from improved experimental design.