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Reproductive timing, location, and behavior are important characteristics that determine marine population dynamics, structure, and resilience to threats, including fishing and climate change. It is challenging to evaluate factors driving variability in these reproductive traits in wild fishes because of the difficulty observing individuals in their natural environments. In the present study, we used high‐resolution depth, temperature, and acceleration time series recorded by pop‐up satellite archival tags to (1) identify and characterize patterns in depth and acceleration that may be indicative of spawning events in large Atlantic halibut (Hippoglossus hippoglossus), and (2) estimate the effects of individual traits (body size and sex) and environmental factors (location and temperature) on spawning time and frequency. Unique rapid rises observed in the winter depth profiles were interpreted as spawning events. The initiation of the first presumed spawning rise was negatively correlated to water temperature experienced during the prespawning season, suggesting that currently increasing water temperature in the Gulf of St. Lawrence may induce phenological change in halibut spawning time. The number of rises of batch‐spawning females was unrelated to female body size. The present study demonstrates how electronic tagging can be used for in‐depth characterization of timing, location, and behaviors associated with spawning in a large flatfish species. Such information can inform spatiotemporal management and conservation measures aiming to protect species from directed fishing and by‐catch during spawning. [ABSTRACT FROM AUTHOR]

Knowledge of the larval ecology of winter‐spawning fish from the Estuary and Gulf of St. Lawrence, Canada, remains scarce due to the seasonal ice cover that prevents ichthyoplankton sampling using conventional methods. Two winter‐spawning species, Atlantic halibut (AH, Hippoglossus hippoglossus) and Greenland halibut (GH, Reinhardtius hippoglossoides), support the most important groundfish fisheries of this area. In March 2020, the authors captured 10 halibut larvae ranging in size from 5 to 14 mm during an opportunistic survey in the GSL onboard an icebreaking vessel. Of these, eight were AH and two GH. Judging by their very small size, the larvae were only a few days old, suggesting that the spawning grounds are close to the capture sites. This effort constitutes a first step in validating the putative spawning areas for these two important GSL stocks. This knowledge is important for the conservation and sustainable management of these fisheries. [ABSTRACT FROM AUTHOR]

Uncertainties in fish tracking studies limit their integration into conservation and fisheries management plans. This is especially true for archival tagging studies that rely on geolocation models to infer fish tracks from recorded environmental variables. Hidden Markov Models (HMMs) are increasingly popular to geolocate marine fish equipped with archival tags; however, true errors and sensitivity of geolocation HMMs are seldom evaluated. In this study, we first review validation methods and implementations of geolocation HMMs to adapt to regional oceanography, fish species and tag data. We then use a case‐study to evaluate strengths and limitations of each validation approach and to illustrate the sensitivity of geolocation HMMs to implementation assumptions. Simulated and fixed tag locations are the most widely implemented methods, but less common methods relying on true fish tracking, that is double‐tagging or distance from recapture experiments, provide more informative estimates of model accuracy and precision. Results showed that model performance can be improved using simple assumptions when pre‐processing tag data rather than using a complex movement behaviour model. In addition, accelerometer show potential to further parameterise geolocation models. Overall, results from our case‐study and previous studies showed that current geolocation HMMs have average errors of ca. 30–50 and 120 km for demersal and large pelagic fish, respectively. We suggest that these errors are acceptable for investigations at the scale of fisheries management units. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic halibut (~100 mg, Hippoglossus hippoglossus) were exposed to Vibrio proteolyticus, a Vibrio spp. isolate, Photobacterium damselae ssp. damselae and five different isolates of Aeromonas salmonicida ssp. achromogenes via an hour-long bath immersion to ascertain their variation in pathogenicity to this fish species. Results were analysed using Kaplan-Meier survival analysis. Analysis of the data from challenges using A. salmonicida ssp. achromogenes revealed three survival values of zero and a spread of values from 0 to 28.43. Challenges using a Vibrio spp isolate, V. proteolyticus and P. damselae resulted in Kaplan-Meier survival estimates of 31.21, 50.41 and 57.21, respectively. As all bacterial species tested could induce juvenile halibut mortalities, they must all be considered as potential pathogens. However, the degree of pathogenicity of A. salmonicida is isolate dependent. [ABSTRACT FROM AUTHOR]

In the early 1990s, the Northwest Atlantic Ocean underwent a fisheries-driven ecosystem shift. Today, the iconic cod ( Gadus morhua) remains at low levels, while Atlantic halibut ( Hippoglossus hippoglossus) has been increasing since the mid-2000s, concomitant with increasing interest from the fishing industry. Currently, our knowledge about halibut ecology is limited, and the lack of recovery in other collapsed groundfish populations has highlighted the danger of overfishing local concentrations. Here, we apply a Bayesian hierarchical spatiotemporal approach to model the spatial structure of juvenile Atlantic halibut over 36 years and three fisheries management regimes using three model parameters to characterize the resulting spatiotemporal abundance structure: persistence (similarity of spatial structure over time), connectivity (coherence of temporal pattern over space), and spatial variance (variation across the seascape). Two areas of high juvenile abundance persisted through three decades whereas two in the northeast are now diminished, despite the increased abundance and landings throughout the management units. The persistent areas overlap with full and seasonal area closures, which may act as refuges from fishing. Connectivity was estimated to be 250 km, an order of magnitude less than the distance assumed by the definition of the Canadian management units (~2,000 km). The underlying question of whether there are distinct populations within the southern stock unit cannot be answered with this model, but the smaller ~250 km scale of coherent temporal patterns suggests more complex population structure than previously thought, which should be taken into consideration by fishery management. [ABSTRACT FROM AUTHOR]

The ontogenic development of neurosensory structures in larval Atlantic halibut, Hippoglossus hippoglossus (L.) was examined using microscopy imaging techniques and analysis. Larval samples were preserved at developmental stages of 444, 486, 528, 570, 612, and 666 degree-days, respectively. Larvae were measured and photographed macroscopically. The fish were then embedded in paraffin for histological processing. 5 μm sequential sections of the anterior of the larvae were cut and stained using hematoxylin and eosin dyes. The resulting sections were examined using an Olympus BX60 compound microscope. The development of neurosensory structures such as neuromasts and sensory papillae were observed throughout all developmental stages of larvae and early development of the lateral line was observed at 666 degree-days. Neuromast frequency increased as larvae matured, suggesting that larvae were approaching their first feeding event towards the end of the sampling period. Possible implications of development on larval first feeding are discussed. [ABSTRACT FROM AUTHOR]

Historically, to compensate for declining catches, fishers have usually shifted from species characterized by high catch rate onto less easily caught species or have moved into new fishing grounds. Such shifts are poorly documented for areas with a long history of exploitation (i.e. North Sea) as they occurred long time before the start of the regular assessments of the marine resources. The Swedish longline fisheries in the Kattegat-Skagerrak and North Sea have a long history that spans over several centuries. These fisheries have historically targeted large demersal predator fish as ling ( Molva molva), cod ( Gadus morhua), Atlantic halibut ( Hippoglossus hippoglossus) and skates (mainly Dipturus spp.). In this study, data from the Swedish longline fisheries from 1859 to 1960 have been collated. The data show that the geographical expansion of the fishery was extensive. At the turn of the 20th century, offshore longlining became concentrated north and west of the Shetlands and Hebrides, and after the WWII, the fishery expanded to Iceland and Rockall. In the offshore fishery, CPUE for the main target species, ling, remained stable, whereas for the other species, with the exception of tusk ( Brosme brosme), CPUE showed a dramatic decline over time. In contrast, in the coastal longlining fishery, severe declines were revealed for all major target species except cod. We argue that the constant search for new fishing grounds in the Northeast Atlantic reflects a dwindling resource, where the fishermen kept the catch rates of ling high by travelling to more and more distant fishing grounds. [ABSTRACT FROM AUTHOR]

Variation in oocyte quality affects sustainability of finfish aquaculture products including Atlantic halibut ( Hippoglossus hippoglossus L.). To have an insight into role of major egg yolk constituents in the oocyte quality, egg fatty acid ( FA), amino acid ( AA) and folate contents were related to normal blastomere symmetry, and fertilization and hatching success. Significant correlations were found between dihomo-γ-linolenic acid ( DGLA, 20:3n6), palmitic acid ( PA, 16:00) and docosapentaenoic acid ( DPA, 22:5n3), and normal blastomere symmetry and survival success. Egg concentrations of myristic acid ( MA, 14:0), oleic acid ( OA, 18:1n9), stearidonic acid ( SA, 18:4n3) and eicosadienoic acid ( EDA, 20:2n6) explained 56 % variation in fertilization success. OA and EDA explained 70 % of variation in blastomere symmetry. Palmitoleic acid ( POA, 16:1n7) and linolenic acid ( LNA, 18:3n3) concentrations explained 57% of variation in hatching success. Egg valine concentrations correlated with fertilization rates, and aspartic acid and leucine correlated with normal blastomere symmetry. Alanine and valine concentrations explained together 45% of variation in fertilization. Glutamic acid and tyrosine concentrations explained 68% of variation in normal blastomere symmetry while serine, arginine and valine explained 36% of variation in hatching. These FAs and AAa may be potential indicators of oocyte quality in Atlantic halibut. [ABSTRACT FROM AUTHOR]

The copepod, Calanus finmarchicus, has potential as a new ingredient in practical feeds for marine fish. Two experiments were conducted to evaluate the nutritional value of C. finmarchicus meals when fed to juvenile Atlantic halibut. The first study determined protein, lipid and energy digestibility coefficients of four C. finmarchicus meals prepared under different processing conditions. The second study evaluated growth and nutrient utilization efficiency of juveniles fed diets containing varying proportions of fish meal, plant meals and C. finmarchicus meal. Moisture, ash, protein, lipid and gross energy contents of the C. finmarchicus meals were 28-93, 74-138, 505-648, 123-269 g kg−1, and 21-26 MJ kg−1, respectively. Protein, lipid and energy digestibilities of C. finmarchicus meals were 91-99%, 90-95% and 90-99%. The digestibilities significantly decreased for the Calanus meals processed at higher temperatures. During the growth study, halibut fed a diet containing 240 g kg−1 C. finmarchicus meal had significantly higher weight gain and growth rate than all other groups. Nitrogen and energy retention efficiencies ranged between 35-45% and 33-43%, and were significantly higher for fish fed 160-240 g kg−1 C. finmarchicus meal than for fish fed plant protein and control diets. The results indicate that growth and nutrient utilization efficiency are improved in Atlantic halibut fed diets supplemented with C. finmarchicus meal. [ABSTRACT FROM AUTHOR]

Fishing mortality and natural mortality rates for Atlantic HalibutHippoglossus hippoglossuson the Scotian Shelf and southern Grand Banks were estimated from a multiyear tagging study. Models that were used to estimate mortality rates incorporated tag loss. Between 2006 and 2008, 1,913 Atlantic Halibut were double-tagged with t-bar anchor tags; as of 26 August 2010, 368 of these fish had been recaptured. We estimated instantaneous fishing mortality (F) separately for each cohort in the first year (on average, 6 months) after release to allow newly tagged animals to mix with the population. A two-parameter model was used to describe tag loss. Tag loss was estimated at 13% per year in the first year and 10% per year in the second and subsequent years. Using the multiyear model with incomplete mixing and assuming 90% tag reporting and 80% survival from tagging, average instantaneous natural mortality (M) of Atlantic Halibut was estimated to be 0.22 andFwas estimated to be 0.15 in 2007, 0.24 in 2008, and 0.18 in 2009. These estimates ofFwere comparable to those from the stock assessment population model. However, the estimates ofMwere higher than inferred estimates ofMbased on life history and growth. Estimates ofFandMwere sensitive to the minimum size of Atlantic Halibut at the time of release. An increase inFwith size is consistent with fishery size selectivity resulting from either gear selectivity or the distribution of fishing effort where there is spatial heterogeneity in the size composition. We suggest thatMmay have been overestimated because of emigration from the study area. Received April 16, 2012; accepted December 11, 2012 [ABSTRACT FROM PUBLISHER]

In this study, we identified and characterized 160 microsatellite loci from an expressed sequence tag (EST) database generated from immune-related organs of turbot ( Scophthalmus maximus). A final set of 83 new polymorphic microsatellites were validated after the analysis of 40 individuals of Atlantic origin including both wild and farmed individuals. The allele number and the expected heterozygosity ranged from 2 to 18 and from 0.021 to 0.951, respectively. Evidences of null alleles at moderate-high frequencies were detected at six loci using population data. None of the analysed loci showed deviations from Mendelian segregation after the analysis of five full-sib families including approximately 92 individuals/family. The markers are used to consolidate the turbot genetic map, and because they are mostly EST-derived, they will be very useful for comparative genomic studies within flatfishes and with model fish species. Using an in silico approach, we detected significant homologies of microsatellite sequences with the EST databases of the flatfish species with highest genomic resources (Senegalese sole, Atlantic halibut, bastard halibut) in 31% of these turbot markers. The conservation of these microsatellites within Pleuronectiformes will pave the way for anchoring genetic maps of different species and identifying genomic regions related to productive traits. [ABSTRACT FROM AUTHOR]

Phenylhydrazine injections (0·3 mg kg−1, followed by a second injection of 0·1 mg kg−1 7 days later) induced a reproducible and stable anaemia in Atlantic halibut Hippoglossus hippoglossus, reducing the haematocrit and haemoglobin by 70·0 and 75·5%, respectively, over 3 weeks. There were no changes in blood electrolyte or lactate concentrations, although anaemic fish showed a 37·5 and 33·0% increase in cardiac somatic index and ventricular somatic index, respectively, compared with dimethyl sulphur oxide (DMSO) and saline vehicle controls. Changes in cardiac somatic indices did not correlate with the ratio of ventricular length:height and length:width did correlate with haematocrit and haemoglobin indicating that changes in cardiac shape may occur as a function of anaemic hypoxemia. [ABSTRACT FROM AUTHOR]

The growth, survival and tag retention of double-tagged [external FT4 lock-on (FT4) and internal passive integrated transponder (PIT)-tagged] Atlantic halibut Hippoglossus hippoglossus were compared to internal PIT-tagged controls in a randomized trial. The objective was to assess the suitability of these tags for monitoring the performance of individual fish in longitudinal trials under commercial cage-culture conditions in the lower Bay of Fundy, New Brunswick, Canada. The FT4 tags were chosen due to their similarity to tags used by investigators to track H. hippoglossus in the wild. A subset of the population randomly received an external FT4 tag inserted through the operculum and were monitored over a 1105 day period. The specific growth rate of FT4-tagged fish was significantly reduced in the first sea summer with no significant difference observed for the remainder of the trial. The differential growth in the first sea summer created a relative size advantage, permitting controls to increase in size significantly faster than FT4 fish in all subsequent periods. The FT4 tags did not significantly influence survival under normal commercial cage-culture conditions. Results, however, suggest that the survival of FT4-tagged H. hippoglossus may be compromised during stressful handling events. Tag retention of FT4 tags was acceptable with 76% of tags remaining at the end of the 1105 day trial. FT4 tags proved to be an effective method to identify individual H. hippoglossus, with the caveat that they seriously bias productivity measures in commercial research trials. [ABSTRACT FROM AUTHOR]

To investigate the interactive effects of temperature and photoperiod on the growth performance, feeding parameters and muscle growth dynamics in juvenile Atlantic halibut ( Hippoglossus hippoglossus L.), a total of 1212 juvenile halibut, including 383 tagged fish (mean initial weight of tagged individuals: 17.6 ± 0.3 g SE), were reared under a simulated natural light regime for Bergen (60°25′N) or continuous light at 9, 12 and 15 °C from 3 December 2007 until 11 March 2008. The mean weight and growth rate were significantly higher at 12 and 15 °C than at 9 °C. In addition, significantly higher mean weight and growth rate were observed in halibut reared under continuous light at a low temperature, indicating an interactive effect of temperature and photoperiod on growth performance. No effect of temperature or photoperiod was found with respect to feed conversion efficiency, whereas a higher feed consumption at increasing temperature and a higher overall daily feeding rate at continuous light at a low temperature were observed. Indications of continuous light having a stronger effect at low temperatures on muscle growth dynamics were found. A difference in the size class distribution of fibre diameter was found between photoperiod treatments at 9 °C, suggesting that continuous light resulted in elevated hypertrophic growth at low temperature. This may suggest that the increased growth rate found at continuous light at 9 °C may be a result of hypertrophic growth in juvenile halibut. [ABSTRACT FROM AUTHOR]

Three isonitrogenous (520 g protein kg−1 DM) and isoenergetic (25 MJ kg−1 DM) diets containing increasing levels of flaxseed oil (FxO; 0%, 40% and 70% of total added oil) at the expense of fish oil (FO) were tested for 33 weeks in groups of 61 individually PIT-tagged halibut (initial weight, 849 ± 99 g). Effects on fish growth performance, fillet nutritional and sensory quality were determined. Specific growth rate (0.2% day−1), feed conversion ratio (1.2-1.3) and nitrogen and energy retention were not affected by dietary treatments. Dietary fatty acid composition was reflected in fatty acid profiles of halibut muscle, liver and heart. Muscle of fish fed FxO diets contained higher 18:2n-6 and 18:3n-3 concentrations whereas 20:5n-3 and 22:6n-3 levels were significantly reduced. However, increasing FO replacement induced preferential retention of 22:6n-3 especially in heart, and a trend for 20:5n-3 conservation in heart and muscle was observed. FO replacement did not affect colour, texture and the characteristic fish odour and flavour of cooked fillets. By selectively retaining long-chain polyunsaturated fatty acids halibut can adapt to a lower dietary supply without adverse effects on growth, feed conversion ratio, survival, and fillet nutritional and sensory quality. [ABSTRACT FROM AUTHOR]

The article offers information on the study related to efficacy of florfrnicol in the treatment of bacterial infections in halibut. It states that at early life stages, Atlantic halibut larvae are susceptible to bacterial infections often caused by opportunistic Vibrio species. It mentions that there were no signs of spiral swimming, or any other signs resembling those that occur during a nodavirus outbreak and it was suggested that the mortality was caused by a bacterial infection.

The efficacy of the anaesthetic agents benzocaine, metacaine (MS-222), metomidate, 2-phenoxyethanol, quinaldine and isoeugenol was studied in Atlantic halibut ( Hippoglossus hippoglossus). Fish with an average body weight of 33 g were anaesthetized at 8 °C and fish with an average body weight of 1243 g were anaesthetized at 8 and 15 °C. Agents were tested individually and as combination anaesthesia comprising pre-anaesthetic sedation, followed by anaesthesia. Induction and recovery times varied in relation to the body weight and water temperature. Large fish had longer induction times and shorter recovery times, and displayed reduced responsiveness to handling compared with small fish. A higher temperature resulted in shorter induction times, longer recovery times and increased responsiveness to handling. Lower dosages were used for all agents in combination anaesthesia. In small fish, this had no effect on the induction times but resulted in shorter recovery times and reduced responsiveness to handling. In large fish, combination anaesthesia resulted in shorter induction times whereas no uniform trend in recovery times and no differences in responsiveness to handling were observed. Neither individual agents nor combinations blocked all reflex reactions to external stimulation in all fish of any treatment group. MS-222 and benzocaine, used separately or in combination anaesthesia, were the most effective agents in reducing reflex reactions. [ABSTRACT FROM AUTHOR]

Studies were conducted with juvenile (28 g) Atlantic cod ( Gadus morhua) and halibut ( Hippoglossus hippoglossus) fed fish meal (FM) based diets with partial (0%, 25%, 50% and 75%) or total (100%) replacement of FM with freeze-dried krill (FDK). Addition of dietary FDK significantly stimulated feeding activity in both species and resulted in higher feed consumption and intakes of digestible protein (DP) and energy (DE). This is a significant finding on the feed attractant properties of FDK because it occurred despite having 2-4 MJ kg higher levels of DE in the FDK diets which could have had an intake suppression effect. In addition, it indicates that the soluble protein fraction of krill thought to be responsible for its attractant properties and is routinely lost or greatly reduced during commercial processing of krill meals, is retained by freeze-drying. Supplementation of FDK significantly improved growth rates, digestibility and nutrient utilization. Levels exceeding 25-50% FM replacement, however, generally did not significantly increase growth performance or nutrient utilization. In addition, feed formulations with high FDK (>75% replacement) are likely to be cost-prohibitive as long as the market price remains higher than FM. [ABSTRACT FROM AUTHOR]

An ontogenetic sequence of Atlantic halibut Hippoglossus hippoglossus larvae, reared in intensive culture conditions, was cleared and stained and histologically processed to determine normal cranial chondrification for specimens ranging from 0 to 41 days post-hatch (dph). Twenty-six cranial cartilaginous structures were described, at daily intervals post-hatch. The ontogenetic trajectory, composed of alternating steps and thresholds, was interpreted as saltatory. In comparison with other flatfishes, H. hippoglossus exhibits delayed onset of chondrification. From 9 dph onwards, the ontogenetic trajectory resembles more than that of the turbot Psetta maxima than that of the common sole Solea solea or the summer flounder Paralichthys dentatus and winter flounder Pseudopleuronectes americanus. Hippoglossus hippoglossus with the gaping-jaw malformation, common in intensively cultured individuals of this species, were examined histologically. The reason larvae cannot close their mouth, as their yolk-sac resorbs, seems to be related to the fusion of the interhyal to the hyosymplectic and ceratohyal with which it is normally articulated. [ABSTRACT FROM AUTHOR]

Atlantic halibut, Hippoglossus hippoglossus (L.), that were cultured in tanks with a smooth bottom (gel-coated fibreglass) substrate developed papillary hyperplasia and skin erosions on the blind (ventral) side. No viruses, bacteria or parasites were observed in any sections of affected skin. Comparison of microscopic pathology with that of skin from normal, wild-caught halibut showed severe epidermal proliferation with foci of severe mucous cell hyperplasia. Both epidermal thickness and mucous cell density were significantly greater in fish held on a smooth substrate compared to skin of healthy fish. Spongiosis was present, especially at the base of the papillary, hyperplastic epidermis, and there was a chronic inflammatory infiltrate in the scale pockets composed of lymphocytes, histiocytes and erythrocytes. Skin erosions had various degrees of epidermal loss, in some cases to the basement membrane. A predisposing factor for the epidermal sloughing may have been related to the spongiosis, and the vacuolated, degenerated basal cells. When affected halibut were cultured for an additional 28, 62 or 97 days on a sand substrate, which is conducive to skin lesion healing, there was no apparent change in epidermal thickness over time. However, mucous cell density significantly increased from day 0 to 97 during the healing process. [ABSTRACT FROM AUTHOR]

During ontogeny, individual fish larvae and juveniles will develop at different paces despite apparently identical age and environment, and even genetic background. The urgent need to elucidate mechanisms critical to juvenile production, recruitment or even lifelong growth patterns implies that measures and results are compared by a meaningful standard such as developmental stage of the individual fish. Characterizations of developmental stages based on relatively invariable characteristics such as the sequence of cranial ossification have proven to be not only commercially and scientifically applicable in Atlantic halibut, but also point to a practical use for a character which is preserved in most fishes examined. Once described, useful proxies for stage determinants may be size parameters such as standard length, or preferably myotome height (particularly for flatfishes). The worst proxy for development of a batch of fish is age, exacerbated by the expense of analyzing irrelevant intervals. [ABSTRACT FROM AUTHOR]

The long-term effects of two salinities (15 and 27‰) on growth, feed conversion efficiency, and blood physiology of Atlantic halibut were investigated. Growth and feed conversion efficiency of juvenile Atlantic halibut was improved by 20% by rearing fish at intermediate salinities (here 15‰). Interestingly, the growth-enhancing effect of lowering the salinity seems to be independent of size and age of the halibut and is not reserved to the initial juvenile stage. A cost benefit analysis indicates that the new farming method has the potential to double the profit of a given halibut farm. Measured blood variables were lower at 15‰ compared with 27‰ while the values were within the range of that earlier described and there were no indications that reduced salinities represented a stressful environment to the fish. Overall, the results indicate that the growth rate, feed conversion, and farming economics can be improved by rearing Atlantic halibut at near intermediate salinities. [ABSTRACT FROM AUTHOR]

Atlantic cod, Gadus morhua, averaging 100 g, were experimentally challenged by intraperitoneal injection of nervous necrosis virus (NNV) originating from Atlantic halibut. Cod tissues, including blood, gill, pectoral fin, barbel, ventricle, atrium, spleen, liver, lateral line (including muscle tissue), eye (retina) and brain, were sampled at day 25 and 130 and investigated by real-time RT-PCR for the presence of NNV. Relative quantifications at day 130 were calculated using the 2−ΔΔCt method. Immunosuppression by injection of prednisolone-acetate was introduced for a 30-day period, and tissue sampled at day 180 and relative quantification estimated. No mortality or clinical signs of disease were observed in the challenged group. The challenge resulted in detection of NNV in blood, spleen, kidney, liver, heart atrium and heart ventricle at day 25, and by the end of the experiment NNV showed a clear increase in brain and retina, suggesting these to be the primary tissues for viral replication. There was no increase in the relative amount of NNV in blood, atrium, ventricle, spleen, liver and kidney. Corticosteroid implants resulted in a weak increase in virus RNA in spleen, kidney, liver and brain. These findings suggest that Atlantic cod is susceptible to infection with NNV from halibut. The observed tissue tropism patterns suggest an initial viraemic phase, followed by neurotrophy. Head-kidney is the best tissue identified for possible NNV detection by non-lethal biopsy, but detection was not possible in all injected fish. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of continuous light at different stages during the production cycle of Atlantic halibut Hippoglossus hippoglossus L. on growth, age at first maturity, endocrine parameters and flesh quality. A group of juvenile halibut [mean (SD), initial weight 191.3 g (44.7)] was reared in indoor tanks under ambient temperature conditions for 38 months until harvesting (mean final weight, 4.6 kg). The entire photoperiod experiment was divided into four phases, where the fish in each phase were exposed to either natural photoperiod (62°33′N) or continuous light (L). Thus, the following five photoperiod combinations were tested: (a) Control group (NNNN), (b) Group 2A (NLNN), (c) Group 2B (NNLN), (d) Group 2C (NNNL) and (e) Production group (LNNN). Exposure to continuous light stimulated growth, and the final mean weights of Groups 2A and 2B were 23% and 11% higher than those of the Control group (NNNN). The final plasma 11-ketotestosteron levels were lower in Groups 2A (2.94 ng mL−1) and 2B (2.46 ng mL−1) compared with the Control (5.29 ng mL−1), Group 2C (5.09 ng mL−1) and the Production group (4.78 ng mL−1) during spring 2007 (age 4 years), indicating higher age at first maturity in Groups 2A and 2B. Photoperiod regime had only a minor, and transient, effect on flesh-quality traits of the fish, whereas a significant seasonal effect was seen with a tendency towards increased gaping, lower pH, lower hardness and lower shear force in July compared with December and March. [ABSTRACT FROM AUTHOR]

The study aims to test whether predigested dietary protein enhances the utilization of formulated diets at weaning, and also whether it stimulates intestinal maturation. In this study, Atlantic cod [ Gadus morhua L.; 41 days posthatch (dph)] and Atlantic halibut [ Hippoglossus hippoglossus L.; 63 days postfirst feeding (dpff)] were weaned onto diets with graded levels of protein hydrolysate. By increasing the inclusion of dietary protein as hydrolysate from 0 to 400 g kg−1, cod increased the rate of survival from 7 ± 1% to 18 ± 2% (82 dph; regression, P = 4*10−7). In halibut, the survival rate decreased from 57 ± 9% to 22 ± 7% as the inclusion of protein in the form of hydrolysate increased from 0 to 450 g kg−1 (119 dpff; regression, P = 8*10−5). Growth was not affected in any of the species. Results in specific activities of the intestinal enzymes leucine aminopeptidase (LAP) and alkaline phospatase (AP) supported the results in survival in halibut and partly also in cod, by showing increased activities in groups with increased survival (anova, P < 0.05). The lower optimal level of hydrolysed protein in halibut than in cod is suggested mainly because of a slower feeding practice in halibut, which allows more extensive nutrient leaching before ingestion. [ABSTRACT FROM AUTHOR]

A sampling method is described to determine accurately the number of fast myotomal muscle fibres ( NF) in a large flatfish species, the Atlantic halibut Hippoglossus hippoglossus. An unusual feature of the fast myotomal muscle is the presence of internalized strips of slow muscle fibres. In fish of 1·5–3·5 kg ( n = 24), the total cross-sectional area ( ATC) of fast muscle was 18% greater in the dorsal than ventral myotomal compartments ( P < 0·05), whereas there was no significant difference between left- and right-hand sides of the body. Due the bilateral asymmetry, muscle blocks (5 × 5 × 5 mm) were prepared to systematically sample each myotomal quadrant (dorsal, ventral, left- and right-side) and the diameters of 150 fast fibres measured per block. Smooth non-parametric probability functions were fitted to a minimum of 800 measurements of fibre diameter per quadrant ( n = 5). There were no significant differences in the distribution of muscle fibre diameters between myotomal compartments and therefore NF could be estimated from a single quadrant. The number of blocks required to estimate NF with a repeatability of ±2·5% increased from six at 300 g body mass to 17 at 96·5 kg, caused by variation within and between blocks. Gompertz curves were fitted to measurements of fibre number and fork length ( LF). The estimated final fibre number was 8·96 × 105 (7·99–9·94 × 105, 95% CI) for males and 1·73 × 106 (1·56–1·90 × 106, 95% CI) for female fish. The estimated LF for cessation of fibre recruitment in the fast muscle of female fish (1775 mm) was almost twice that in males (810 mm), reflecting their greater ultimate body size. [ABSTRACT FROM AUTHOR]

An oligonucleotide microarray containing 50-mer oligonucleotides representing 9277 unique Atlantic halibut Hippoglossus hippoglossus genes has been designed, printed and is currently being used for the study of gene expression in developing halibut. The oligonucleotides are based on all the Atlantic halibut data available at the time of printing, these included expressed sequence tags (ESTs) and complete cDNAs derived from the Pleurogene sequencing project as well as sequences deposited in GenBank by other groups as of September 2006. Of the Pleurogene ESTs, 5040 are functionally annotated; the remainder are unknown (1016) or are similar to unannotated sequences in GenBank (1626). In addition to Atlantic halibut features, several control features have been incorporated, including an oligonucleotide representing a heterologous plant gene (92 spots) and empty spots containing buffer only (1344). The array contains 48 subgrids, each comprised of 32 columns and 26 rows. Every feature is printed at least four times as side-by-side quadruplicates, resulting in a microarray containing 39 936 features. This microarray has been utilized to identify genes differentially expressed in larval Atlantic halibut during the developmental period from post-hatch to post-metamorphosis. Early in development, transcription of the gene for hatching enzyme was down-regulated, whereas a gene involved in eye development was up-regulated. Midway to metamorphosis, transcription of genes encoding several key digestive enzymes was up-regulated, and in pre-metamorphic larvae, transcription of genes encoding muscle proteins was prominent. [ABSTRACT FROM AUTHOR]

The effects of partial replacement of fish meal (FM) with meal made from northern krill ( Thysanoessa inermis), Antarctic krill ( Euphausia superba) or Arctic amphipod ( Themsto libellula) as protein source in the diets for Atlantic salmon ( Salmo salar L.) and Atlantic halibut ( Hippoglossus hippoglossus L.) on growth, feed conversion, macro-nutrient utilization, muscle chemical composition and fish welfare were studied. Six experimental diets were prepared using a low-temperature FM diet as control. The other diets included northern krill where 20, 40 or 60% of the dietary FM protein was replaced with protein from northern krill, and two diets where the FM protein was replaced with protein from Antarctic krill or Arctic amphipod at 40% protein replacement level. All diets were iso-nitrogenous and iso-caloric. Atlantic salmon grew from 410 g to approximately 1500 g during the 160 day experiment, and Atlantic halibut grew from 345 g to 500–600 g during the 150 day experiment. Inclusion of krill in the diets enhanced specific growth rate in salmon, especially during the first 100 days ( P < 0.01), and in a dose–response manner in halibut for over the 150 day feeding period ( P < 0.05). Feed conversion ratio did not differ between dietary treatments, and no difference was found in dry matter digestibility, protein digestibility and fish muscle composition. Good growth rates, blood parameters within normal ranges and low mortalities in all experimental treatments indicted that fish health was not affected either Atlantic salmon or Atlantic halibut fed the various zooplankton diets. [ABSTRACT FROM AUTHOR]

Atlantic halibut ( Hippoglossus hippoglossus) achieve a mature gastrointestinal tract approximately 2 months after first feeding (12 °C). The immature digestion may be the reason that compound diets fail to sustain growth and survival in first feeding halibut larvae and in larvae of other marine fish species. On the other hand, larvae fed with live feeds are capable of extraction of sufficient quantities of nutrients to sustain high growth rates. A lower availability of the protein in formulated diets compared with live prey is considered to be an important reason for the low performance of formulated diets. One approach to increase dietary protein availability is supplementation of pre-digested proteins. Experiments using tube fed individual larvae show that halibut larvae are able to utilize hydrolysed protein more efficiently than intact protein. However, Atlantic halibut in culture did not respond well to dietary supplementation of hydrolysed protein, in contrast to some other species. One reason may be extensive leaching of pre-hydrolysed proteins from the microparticulate feed. Atlantic halibut are slow feeders and may thus suffer more from nutrient leaching than species eating more rapidly. Feed formulation techniques affect dietary protein leaching, and in this paper, different techniques and their impact on feed properties are described. Microbound diets are most widely used in larval rearing, but show high rates of nutrient leaching. Lipid-based capsules seem to have the best potential to prevent leaching, however, they are not able to deliver a complete diet. The high need for improvements in larval feed formulation techniques are clearly stated, and some suggestions are given. Among these are production of complex particles, where small lipid-based capsules or liposomes containing the low molecular weight water-soluble nutrients are embedded. In such feed particles the water-soluble molecules are protected from leaching. Techniques for delivery of water-soluble nutrients that are needed in large quantities, i.e. free amino acids or hydrolysed and water-soluble protein, remain to be developed. [ABSTRACT FROM AUTHOR]

To determine the effect of maturation on flesh quality, 20 Atlantic halibut ( Hippoglossus hippoglossus) consisting of mature and immature fish of both sexes were killed on site, exsanguinated and stored on ice. After 6 days of storage, the fish was gutted and filleted before colour, texture hardness and shear force were evaluated to determine the effect of maturation. Results show that mature males excreted black mucus from the skin during ice storage, while a greyish mucus was observed from immature fish. Mature fish had approximately 2% lower slaughter yield and 6% lower fillet yield compared with immature fish. The fillets from mature males were significantly harder compared with fillets from immature fish and the muscle structure proved to be stronger as an increased fracturability was observed in mature fish. In colour, fillets from mature fish proved to have a whiter appearance ( L*) than immature fish, while no difference was seen in a* and b* values. We conclude that the physiological changes associated with maturation affects the end quality, and may be related to slower growth. [ABSTRACT FROM AUTHOR]

Atlantic halibut juveniles, which have been fed Artemia during larval development, frequently demonstrate malpigmentation and impaired eye migration. This is in contrast to the high percentage of normally developed larvae fed copepods, reared under similar conditions. Nutrition is therefore an important component influencing larval development. Analyses of the nutrient composition of Artemia and copepods show that Atlantic halibut larvae fed Artemia probably receive sufficient amounts of vitamin A by converting canthaxanthin, while iodine may be deficient, possibly leading to interrupted thyroid hormone synthesis. An unbalanced fatty acid composition, such as high levels of arachidonic acid and low levels of docosahexaenoic acid, can be another limiting factor in Artemia. Vitamin A, fatty acids and thyroid hormones have all been shown to affect pigmentation in flatfish. They are ligands to nuclear receptors, thyroid hormone receptors, retinoic acid receptors, retinoic X receptors and peroxisomal proliferator-activated receptors, which are members of the superfamily of steroid hormone receptors. The receptors interact with each other to promote gene expression that modulates proliferation and differentiation of cells. Our hypothesis is that these interactions are important for development during flatfish metamorphosis. Very little data exist on the topic of impaired eye migration. However, energy limitation, iodine deficiency and an unbalanced fatty acid composition have been proposed as possible explanations. Here, we review the literature on development of pigment cells and the possible mechanisms behind the effects of vitamin A, fatty acids and thyroid hormone on pigmentation and eye migration during development of Atlantic halibut larvae. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic halibut cultured on a smooth substrate often develop skin lesions on the blind (abocular) side, significantly reducing carcass value and causing economic losses. We discovered that fish not only developed skin erosions, but also extensive epidermal papillomas when held on a smooth substrate for 39 months. This is the first time that epidermal papillomas have been reported in Atlantic halibut. To determine whether substrate type affected the progression or healing of these lesions, fish with papillomas and skin erosions were moved to identical rearing units having either an irregular (sand, gravel or Netlon®) substrate, or a smooth (gel-coated fibreglass) substrate. After 62 days, 42–50% of fish held on any of the three irregular substrates had a skin erosion area (SEA) that had either diminished or appeared to be completely healed via gross examination. In contrast, none of the fish held on the smooth substrate showed improvement and 75–100% had a more severe SEA. Changes in the papilloma area (PA) were less dramatic: none of the fish held on an irregular substrate had any clear change in PA, although there was a suggestion that the PA in some fish might becoming less severe. Similarly, none of the fish held on the smooth substrate had a change in PA, although there was a suggestion that the PA in some fish was becoming more severe. After 97 days, there was also a suggestion that specific growth rates were higher in fish held on an irregular substrate when compared with those held on the smooth substrate. Overall, these data further substantiate previous studies suggesting that an irregular substrate, including the commercially used Netlon ®, is best for rearing Atlantic halibut. While there was a clear relationship between substrate type and whether skin erosions or papillomas progressed or healed, the exact cause(s) of these two responses is uncertain. Future studies should focus on risk factors such as stress, burrowing behaviour and the microenvironment of the substrate. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic halibut, Hippoglossus hippoglossus (initial weight (SD) 191.3 (± 44.7)) g, were reared for 99 days at a constant temperature of 11 °C and subjected to three different light regimes from 13 September to 21 December: continuous light (LD24:0), simulated natural photoperiod of Bergen (60°25'N, LDN) and constant 20 h light:4 h dark (LD20:4). The fish reared on the different photoperiod regimes differed in their growth patterns as juveniles exposed to long days, i.e. LD20:4 and LD24:0, exhibited faster growth than those experiencing a natural photoperiod. The LD20:4 group showed the highest average specific growth rate (0.72% body weight day-1), whereas fish on LDN displayed the lowest average specific growth rate (0.60% body weight day -1). The final mean weights of the LD20:4 and the LD24:0 groups were 15% and 12% higher than those of the LDN group. Dividing the duration of the experiment into three time periods shows that the LD20:4 and LD24:0 had a higher feed conversion efficiency (FCE) as compared with the LDN group during the first and the last period, while a reversed situation was observed in the second period. Our data indicate a larger variation in growth rates among individuals in the best-performing groups (here LD20:4 and LD24:0). This may indicate that formation of size hierarchies is more pronounced in groups with more homogenous growth (here LDN). Overall, our findings indicate that extended light regimes result in faster growth and better feed conversion in juvenile Atlantic halibut. In line with findings on other flatfish species, this supports the concept that constant long day:short night or continuous light regimes should be used by the farmer in order to maximize growth and improve feed conversion in Atlantic halibut. [ABSTRACT FROM AUTHOR]

In this study experimental challenges with Moritella viscosa, the causative agent of winter ulcers in salmonids, were performed on juvenile Atlantic cod and Atlantic halibut. The challenges involved both intramuscular (i.m.) and intraperitoneal (i.p.) injections and bath with a strain originally isolated from Atlantic salmon. Cod was found to be significantly more sensitive than halibut to the infection. Both fish species were found to be more sensitive to i.m. than i.p. challenges. Both challenges induced a systemic disease in cod and halibut, but only cod was infected with an experimental bath challenge. Pathognomonic signs were found to be comparable with those described in M. viscosa-infected salmon and turbot. The main distinguishing pathological sign was that the cod showed host response to M. viscosa infection resulting in granuloma formation in infected tissues, which is a known response of cod to a infection with another Gram-negative bacterium, Aeromonas salmonicida. Re-isolation of M. viscosa from kidneys of cod and halibut with clear disease signs was problematic and optimization of isolation measures is needed. The results of this study indicate that M. viscosa infection may be a risk factor in cod farming, but that halibut is more resistant. [ABSTRACT FROM AUTHOR]

The process of eye migration in bilaterally symmetrical flatfish larvae starts with asymmetrical growth of the dorsomedial parts of the ethmoid plate together with the frontal bones, structures initially found in a symmetrical position between the eyes. The movement of these structures in the future ocular direction exerts a stretch on the fibroblasts in the connective tissue found between the moving structures and the eye that is to migrate. Secondarily, a dense cell population of fibroblasts ventral to the eye starts to proliferate, possibly cued by the pulling forces exerted by the eye. The increased growth ventral to the eye pushes the eye dorsally. Osteoblasts are deposited in the dense cell layer, forming the dermal part of the lateral ethmoid, and at full eye migration this will cover the area vacated by the migrated eye. When the migrating eye catches up with the previous migrated dermal bones, the frontals, these bones will be remodelled to accommodate the eye. Our findings suggest that a combination of extremely localized signals and more distant factors may impinge upon the outcome of the tissue remodelling. Early normal asymmetry of signalling factors may cascade on a series of events. [ABSTRACT FROM AUTHOR]

Flatfish metamorphosis is initiated by the actions of thyroid hormones (TH) and iodine is an essential part of these hormones. Hence, an iodine deficiency may lead to insufficient levels of TH and incomplete metamorphosis. In this study, different iodine sources for enrichment of Artemia were evaluated and the levels of iodine obtained in Artemia were within the range of 60–350 μg g−1 found in copepods. Larval Atlantic halibut was fed Artemia enriched with either normal DC-DHA Selco or DC-DHA Selco (commercial enrichments) supplemented with iodine from days 9 to 60 postfirst feeding. There was no significant difference in growth, mortality or metamorphic development between the groups. The analyses showed that we were able to enrich Artemia with iodine. Further, the larvae-fed iodine-enriched Artemia had higher whole body iodine concentration compared to larvae-fed Artemia without iodine enrichment. [ABSTRACT FROM AUTHOR]

The article discusses the growth improvement of malpigmentation in juvenile turbot Scophthalmus maximus Rafinesque and halibut Hippoglossus hippoglossus L. Skin malpigmentation is common cultured flatfish and halibut, while malpigmented juveniles are seen undesirable for further culture. A review on the development of pigments in hatchery-reared flatfishes were conducted with emphasis on two developmental explanations for malpigmentation in flatfishes. The study showed a notable difference in growth at 16 degrees Celsius, on higher growth in all periods at 13 degree Celsius and on the average at 6 percent. Further investigation of the growth dynamics between malpigmented and normally pigmented turbot shows that the optimal temperature for growth is almost identical.

To explore the population structure of Atlantic halibut Hippoglossus hippoglossus, 160 fish from four locations in the north-west Atlantic (Bay of Fundy, Scotian Shelf, Gulf of St Lawrence and Iceland) were examined for evidence of population structure using 18 microsatellite markers. Pair-wise FST and a model-based cluster analysis revealed no significant differentiation between samples, although uncertainties surrounding Atlantic halibut reproductive behaviour made it difficult to ascertain that only a single breeding population had been sampled at each location [ABSTRACT FROM AUTHOR]

Four experiments were conducted to investigate the effects of feeding frequency on growth of juvenile Atlantic halibut,Hippoglossus hippoglossusL. Fish (22–75 g) fed three (3×) or five times per day (5× day−1) under constant light and temperature (13±1°C) consumed significantly more feed than fish fed 1× day−1 but by the end of the experiment only fish fed 5× day−1 were heavier and had greater specific growth rates (SGR). Under simulated winter conditions (9L:15D, 5±1°C), halibut (∼300 g) fed every other day consumed more feed, had a greater SGR and final weight compared with fish fed every third day. Feed conversion ratios were not different among treatment groups in any of the experiments. These results suggest that growth rates may be improved by feeding juvenile halibut more than 1× day−1. [ABSTRACT FROM AUTHOR]

The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut. The halibut were reared at 11°C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light on 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. Juveniles subjected to continuous light exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, the results suggest an overall growth enhancing effect of continuous light in females, but not in males. No females matured during the trial, but the proportion of mature males differed between the photoperiod groups, with significantly fewer males maturing in groups reared at continuous light. Independent of photoperiod regime and maturation status, females were significantly bigger than males from 14 April 1997 onwards. Immature males were bigger than maturing males from 23 March 1996 onwards. As continuous light reduced maturation at age 2+ in males, this could be used to reduce precocious maturation in males. [ABSTRACT FROM AUTHOR]

First-feeding halibut larvae (245-day degrees; 40 days post hatch), reared at 34 g L−1 salinity and 7°C, were subjected to handling and allowed to recover in a range of salinities (0–34 g L−1) and at 10°C. Survival of the unfed larvae was determined daily for 18 days. Mortality rates approached 0 after 4 days in all treatments and presumed starvation-induced mortality started at about 11 days post handling. By 20 days post treatments, all larvae had died. Salinities in the range of 10–20 g L−1 produced significantly (anova,P<0.01) higher initial survival (71–95%) than salinities above 20 g L−1 (24–48%) or below 10 g L−1 (0–19%) and this survival pattern changed little in unfed larvae for the first 10 days following the stressor. For example, 24 hour post handling, survival of halibut was improved from 28.7±16.5% (mean±standard error,n=3) at 34.0 g L−1 to 95.2±4.8% at 13 g L−1. A second-order polynomial regression of 4-day post-handling survival data (y=−0.0022+0.0603x+0.0699,r2=0.3936) predicted a maximum survival at 15.1 g L−1 salinity. These results have important implications for halibut aquaculture and research when handling of larvae is unavoidable. For practical applications, we recommend reducing salinity of receiving waters to 15–20 g L−1 with a slow (3–4 days) reacclimation to ambient conditions. [ABSTRACT FROM AUTHOR]

Atlantic halibut ( Hippoglossus hippoglossus L.) larvae were fed enriched Artemia or zooplankton in duplicate tanks from 0 to 60 days after first-feeding. Both diets and the larvae were analysed for vitamin A (VA) in order to confirm earlier findings, in which Artemia fed larvae had lower levels of VA compared with larvae fed zooplankton. Furthermore, we wanted to investigate the composition of the retinoids in the larvae. The results showed that Artemia and zooplankton contains low levels of VA, probably too low to sustain the assumed requirement. Nevertheless, larvae fed Artemia had the same level of retinal and retinol as larvae fed zooplankton. We found a significant lower level of retinyl esters in larvae fed Artemia. The total VA level was lower in larvae fed Artemia only at the end of the feeding trial after the onset of metamorphosis. Our conclusion is that feeding Artemia to Atlantic halibut larvae is not likely to cause VA deficiency. [ABSTRACT FROM AUTHOR]

Following a natural outbreak of viral encephalopathy and retinopathy (VER) at a commercial farm in Norway, surviving Atlantic halibut, Hippoglossus hippoglossus, were sequentially studied for distribution of nodavirus, immune response and histopathology over 1 year. Typical clinical signs and histopathology of VER were observed during the acute stage of the disease. Most of the surviving fish became subclinical carriers of nodavirus with clusters of nodavirus-containing cells in the central nervous system. Four random samplings of presumably healthy fish were performed from two fish groups, with low and high growth rates respectively, over a 7-month period. Immunohistochemical (IHC) examination revealed a higher number of nodavirus-positive cells in fish with a low growth rate than in fish with a high growth rate. All IHC positive fish were also reverse transcriptase polymerase chain reaction (RT-PCR) positive for nodavirus and for nodavirus antibodies detected by enzyme-linked immunosorbent assay (ELISA) at all sampling points. The percentage of PCR- and ELISA-positive fish remained high throughout the year, while the number of IHC-positive fish decreased, especially in the group with a high growth rate. Several other histopathological changes were observed, including pericarditis, steatitis, changes in liver and kidney, and necrosis of the intestinal wall. None of these findings seemed to be related to the nodavirus infection. Nodavirus was reisolated in cell culture from subclinically infected fish one year after the acute VER outbreak, which indicates that the virus was still infectious. [ABSTRACT FROM AUTHOR]

The present study investigated the distribution of α-tocopherol (vitamin E) in fillets of turbot ( Scophthalmus maximus) and Atlantic halibut ( Hippoglossus hippoglossus). Turbot and Atlantic halibut were fed commercial diets, supplemented with different levels of α-tocopheryl acetate at the dietary target levels of 100, 500 and 1000 mg α-tocopheryl acetate kg−1 diet. The actual levels were 72, 547 and 969 for turbot, while halibut received 189, 613 and 875 mg α-tocopheryl acetate kg−1 diet. Turbot were fed the diets for 24 weeks, while Atlantic halibut were fed for 20 weeks prior to slaughter. At the end of the feeding periods fish had reached a final weight of around 1 kg. Fish were slaughtered and filleted. From the four fillets obtained per fish, 22 samples were taken from designated areas and analysed for their α-tocopherol content. The average concentrations of α-tocopherol incorporated in turbot and Atlantic halibut increased with increasing levels of α-tocopheryl acetate in the diet. Atlantic halibut had significantly ( P < 0.05) more α-tocopherol in positions 2/II and 1/I than in position 9/IX. Turbot had significantly ( P < 0.05) more α-tocopherol in position 2/II than in positions 1/I, 4/IV and 11/XI. By mapping α-tocopherol concentrations in fish fillets, a high degree of quality prediction may be established. Moreover, this study may help scientists in their choice of sampling position, when investigating if α-tocopheryl acetate supplementation resulted in successful α-tocopherol incorporation. [ABSTRACT FROM AUTHOR]

Abstract Folate mobilization from the yolk compartment during larval development was studied by analysing the folate concentration in whole body, embryo and yolk in a single batch of Atlantic halibut, Hippoglossus hippoglossus L., eggs and larvae that showed successful fertilization and development. There was a net loss of approx. 50% of folate from yolk during endogenous feeding. Further, only 23% of the decrease in yolk folate was retained in the larval body. The data suggest a need for folate for metabolic and growth purposes during embryogenesis of approximately 2 μ g g-1 weight gain. Relative to these data and published folate requirement for cold-water species, batches of egg from 16 Atlantic halibut brood fish contained variable and, for some batches, critically low levels of folate. This may constitute a potential problem for larval development until start feeding. [ABSTRACT FROM AUTHOR]

Abstract Atlantic halibut, Hippoglossus hippoglossus (L.), was shown to be sensitive to infection by three different isolates of Aeromonas salmonicida ssp. achromogenes in pre-challenge tests using intraperitoneal (i.p.) and intramuscular (i.m.) injections as well as bath challenges. A commercial furunculosis vaccine, Alphaject 1200, and an autogenous vaccine, AAS, based on the challenge strain, induced immune protection as shown in challenge tests 8 weeks post-immunization. The survival rate of vaccinated fish after i.p. challenge was 100%, whereas mortality of control fish was 61%. Employing i.m. challenge, relative percentage survival induced by the furunculosis vaccine and the AAS vaccine was 47 and 44, respectively. Mortality of i.m. injected controls was 68%. Vaccinated fish behaved normally following vaccination but the weight gain was significantly reduced in vaccinated fish 8 weeks post-vaccination compared with control fish receiving phosphate-buffered saline. At the same time, intra-abdominal adhesions were observed in fish injected with either of the two vaccines or adjuvant alone. Antibody response against A. salmonicida ssp. achromogenes was detected in sera from fish receiving either vaccine. [ABSTRACT FROM AUTHOR]

Abstract The susceptibility of Atlantic halibut, Hippoglossus hippoglossus (L.), to viral haemorrhagic septicaemia virus (VHSV) was tested. Juvenile halibut of approximately 5 g weight were subjected to challenge by intraperitoneal injection, cohabitation and immersion to a VHSV isolate from an outbreak of the disease in turbot, Scophthalmus maximus (L.). The intraperitoneal injection gave the highest mortality rate of 28% after 50 days. The cohabitee group suffered 19% mortality rate and the immersion group only 2%. Control groups included turbot exposed either by intraperitoneal injection or immersion which suffered mortality rates of 93 and 50%, respectively. The results suggest that halibut are markedly less susceptible to VHSV than turbot. [ABSTRACT FROM AUTHOR]

Isonitrogenous and isocaloric diets containing 0, 18 or 36% toasted full-fat soybean meal (FFSM) were fed to Atlantic halibut. The diets were fed to five tanks of fish each for 34 days (period 1). Four tanks from each treatment were then retained in the growth experiment for a further 32 days (period 2), while the groups of fish from one tank from each of the 0 and 36% FFSM groups were split and transferred to two metabolism tanks each. The initial weight of the fish in the growth trial was 169 ± 1 g (mean ± SEM, n =12; weight range 89–253 g) and the final weight was 317 ± 5 g. There was no significant effect of dietary treatment on specific growth rate (range, 0.8–1.1% day-1 ), feed consumption (0.5–0.7% body weight day-1 ), feed efficiency (1.3–1.6 g wet gain g dry feed-1 ), protein retention (48–55%) or energy retention (49–57%). The fat, protein and energy concentrations in the fish increased during the trial and were not affected by the diet. The hepatosomatic index in fish fed with 36% FFSM diet was significantly lower (1.7%) than in the other groups (2.2%) (P < 0.05). No differences in intestinal morphology were observed between dietary treatments and no pathological reactions were identified in any of the samples. In the metabolism trial, there were no significant differences in oxygen consumption or ammonia excretion between fish fed with 0 and 36% FFSM diets. In conclusion, up to 36% FFSM may be added to diets for Atlantic halibut without negative effects on growth, feed efficiency or intestinal morphology. [ABSTRACT FROM AUTHOR]

Fish fillet quality may be influenced by the antioxidant level in preslaughter diet. Thus, the effects of dietary α-tocopheryl acetate supplementation and feeding time on the flesh quality of farmed Atlantic halibut Hippoglossus hippoglossus L. were investigated. Halibut of mean initial weight of 312 ± 12.3 g were divided into two groups and fed commercial diets, supplemented with different levels of α-tocopheryl acetate at the dietary inclusion levels of 189 and 613 mg kg -1 diet. Fish were sampled after 6,9,12 and 24 weeks. Over the experimental period, they reached a final mean weight of 1320 ± 108.4g. Tissue α-tocopherol of fillet and liver was significantly affected by the levels of α-tocopheryl acetate given with the diets (P < 0.001). In storage on ice, fillets of fish fed the diets high in α-tocopheryl acetate exhibited significantly lower (P < 0.001) levels of lipid oxidation. The colour of fillets in all groups deteriorated slightly, but diet did not affect this process. Halibut fed the supplemented diets for longer periods were better protected against lipid oxidation (P < 0.001) and colour deterioration (P < 0.01) than those fed for shorter periods. However, after 9 days of storage, lipid oxidation levels were still extremely low [< 0.6 µg malondialdehyde (MDA) g -1 fillet], even in fillets of fish fed the low α-tocopheryl acetate diet for a short period preslaughter. Different slaughtering methods tested at the end of the trial showed that percussive stunning can delay the onset of rigor morris by 8-12 h compared with bleeding of the fish. These results suggest that halibut fillets have enhanced shelf-life stability even at low doses of dietary α-tocopheryl acetate, and that other factors in the antioxidant defence mechanisms of the species might play a major role in the prevention of lipid oxidation. [ABSTRACT FROM AUTHOR]

At 7 days after first feeding (DAFF), the peptide hormone cholecystokinin (CCK) content (fmol individual−1) and the tryptic activity [μmol arginine-methyl-coumarinyl-7-amide (MCA) min−1 individual−1] per individual gut of Atlantic halibut Hippoglossus hippoglossus larvae were low: 0·2±0·1 and 0·14±0·10, respectively. Thereafter, both parameters increased with the increase in gut mass and reached 19·67±5·58 and 2·71±0·64 at 26 DAFF, respectively. Due to the small sample size, the dry mass (MG, mg) of the individual gut could not be determined accurately at 7 DAFF. At 13 DAFFMG represented 5·5% of whole body dry mass (MW, mg) while at 26 DAFF it had increased to 23%. The mass specific tryptic activity [μmol MCA min−1 per mg dry mass (M)] in the gut increased from 2·74±1·98 at 13 DAFF to 5·00±0·78 at 26 DAFF. There was more individual variation in the mass specific CCK content (fmol M−1) but no significant differences were found, although the data indicated an increase (from 23·38±11·26 at 13 DAFF to 36·27±8·96 fmol M−1 at 26 DAFF). At 7 DAFF the CCK content of the gut represented c. 2% of the whole body CCK content while it increased to c. 62% of the whole body CCK content at 26 DAFF. This demonstrates that it is necessary to separate neural and gastrointestinal sources of CCK in order to determine its alimentary role in fish larvae. Trypsin activity was only found in the gut compartment. In larvae aged 45 DAFF dietary proteins delivery into the gut by tube-feeding appeared to stimulate post-prandial secretion of CCK from the gut as well as stimulate pancreatic trypsin secretion, suggesting that both factors contribute to protein digestion. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]