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Spotted wolffish (Anarhichas minor) is a promising candidate for diversification of cold-water aquaculture. An increased knowledgebase is needed concerning the capacity of spotted wolffish to utilize a variety of feed ingredients such as microalgae and terrestrial plants. The aim of the study was therefore to investigate the effect of incorporating graded levels of microalgae (Nannochloropsis oceanica) on fish welfare indicators (growth, hepasomatic index, hematological parameters), fast muscle cellularity, chemical and fatty acid composition. Three isonitrogenous and isocaloric diets were formulated; one control diet (0% N. oceanica) and two diets with low (7.5% N. oceanica) and high (15% N. oceanica) levels of microalgae replacing fishmeal and wheat in the diets. After 12 weeks of feeding, the fish showed low growth compared to previous wolffish studies (0.26% SGR). However, this effect was not treatment dependent as there were no differences in growth or fast muscle cellularity among the three treatment groups and hematological parameters showed no indications of stress in the fish fed microalgae. Hepatosomatic index decreased over the course of the experiment for all treatment groups; a significantly larger reduction was noted in the algae-fed fish compared to the control. The omega-3 fatty acid EPA increased in the whole body of the fish fed diets containing microalgae. The results suggest that spotted wolffish has potential to utilize inclusions of up to 15% of the microalgae N. oceanica.

The spotted wolffish (Anarhichas minor) is considered a promising species for coldwater aquaculture. It is a sedentary, bottom-dwelling fish which exhibits a calm and “non-stressed” behaviour in captivity. There are, however, no reports on the physiological responses to stressors in this species. In the present study we investigated primary (cortisol secretion) and secondary (glucose mobilization) responses to common aquaculture stressors like disturbance and hypoxia. Pre-stress plasma cortisol levels were within those generally considered representative for unstressed fish (~ 10 ng ml− 1), whereas basal glucose levels were unusually low (0.3–0.4 mM). After exposure to a short, but severe disturbance challenge (emptying the tank of water for 10 min), the increase in plasma cortisol level was slow and relatively weak, reaching a peak level of 25 ng ml− 1 4 to 8 h after disturbance. When the fish were exposed to a gradually decreasing oxygen level in the tank, a significantly elevated plasma cortisol level (35 ng ml− 1) was seen in the fish that remained in the tank until oxygen saturation had decreased to 20% oxygen saturation after 2.5 h. However, a two-fold higher plasma cortisol level (~ 70 ng ml− 1) was seen in all fish exposed to reduced oxygen levels (60, 40 and 20% oxygen saturation) after 3.5 h recovery in normoxic water. Plasma glucose levels showed only moderate increases (~ 70%) following disturbance and hypoxia challenges. An in vivo injection of ACTH caused a strong elevation of plasma cortisol (peak level ~ 170 ng ml− 1), demonstrating a high capacity for interrenal steroidogenesis in the spotted wolffish. The slow and relatively weak cortisol response to stressors, and low plasma glucose levels, may relate to the sedentary lifestyle of the spotted wolffish. The stress-response is characterised by a passive (reactive) coping style, which is considered adaptive for farming of this species.

Flat-bottom sea cages offer a cost-effective alternative for culture of bottom-dwelling fish. In an experiment lasting 428 days, spotted wolffish (Anarhichas minor Olafsen) grew equally fast when kept in tanks on land and in a flat-bottom sea cage at the same stocking density (increasing from 7.5 to 42 kg m− 2 during the experiment) and same water temperature. A lag phase of 1 month with negative growth was observed following transfer from tanks to the sea cage. The results confirm that flat-bottom sea cages may be an option for culture of this species.

Despite larval robustness characterized by the absence of metamorphosis and readiness for exogenous feeding based on commercial feed, the spotted wolffish (Anarhichas minor) displays highly variable survival at first-feeding. In this study, we investigated the use of three dietary concentrations of protein hydrolysates (PH, pre-digested proteins) (0, 10 and 20%) when newly hatched juvenile wolffish were held at three different rearing temperatures namely, 5, 8 and 12 degrees C to determine whether digestion of protein was a limiting factor for fish growth and survival. Final weights for fish at 5, 8,and 12 degrees C at day 60 were respectively 0.35, 1.19 and 2.02 g. Mean specific growth rates were 1.97, 4.01 and 4.88%/day and survival rates were 49.8, 53.4 and 33.2% respectively. No significant effects of PH were observed on growth or survival at any time during the experiment. However, as a general trend, fish survival was always higher when the diet contained 20% PH. We suggest that the degree of hydrolysis of the PH used may have been insufficient to induce specific digestive enzyme stimulation for promoting larval growth. Moreover, precocious ontogeny of the digestive system may have precluded any significant effect of using dietary protein hydrolysates. Our results are discussed in comparison with metamorphic species which characteristically display incomplete development of the digestive system. (c) 2006 Elsevier B.V. All rights reserved.

Farmed spotted wolffish (Anarhichas minor O.) is susceptible to infections with atypical Aeromonas salmonicida, and experimental oil-adjuvanted vaccines are previously reported to induce protection against the disease. For prophylactic treatment of juveniles, an immersion vaccine is the preferred alternative, and to test the efficacy of different bath vaccination strategies, a waterborne challenge model has to be established. Exposing the wolffish juveniles to 2×107–108 live bacteria ml−1 for 60–90 min resulted in 70–85% mortality. Bath vaccinating wolffish juveniles (∼25 mm) for 1 h in a bacterin containing 108 inactivated cells ml−1 did not induce specific antibody responses although the bacterial antigens were localised in the muscle, kidney and liver tissues. No protection was established in the bath vaccinated fish after waterborne challenge, nor did a second immersion boost improve the efficacy. For comparison, fish were i.p. vaccinated with an oil-emulsified bacterin and significant protection against the pathogen was induced both after injection and bath challenge. The protection was significantly higher when both the vaccine and the pathogen were administered by injection as compared to i.p. vaccination and challenge by bath.

The effects of chronic un-ionised ammonia (UIA) exposure on growth and food conversion efficiency (FCE) in spotted wolffish, Anarhichas minor Olafsen, were examined. Fish with a mean (S.D.) initial weight 14.2 (5.0) g were reared in shallow raceways (initial stocking density of 3.9 kg m −2 ) and exposed to four concentrations of UIA [0.0006 (control), 0.13 (low), 0.25 (medium) and 0.39 mg l −1 (high)] for 69 days at 8.3 °C, 33‰ and pH 8.1. Growth rates were significantly influenced by UIA concentrations, as the control and low-concentration group performed better than both the medium- and high-concentration group, and the medium group in turn displayed a higher growth rate than the high-concentration group throughout the experimental period. While experiencing negative growth rates in the first period, growth rates increased and were positive in fish from both the medium and high group in the second and third period, indicating an adaptation to ambient UIA. At the end of the experiment, mean weights were 13% and 40% lower at UIA concentrations of 0.13 and 0.25 mg l −1 , respectively, when compared to the control group, whereas an overall decrease in mean weight was observed at 0.39 mg UIA l −1 in the experimental period investigated. The difference in growth performance is mainly attributed to variations in daily feed consumption, which varied significantly between all treatments throughout the experiment and decreased with increasing concentrations of UIA, and to a lesser extent by a decrease in food conversion efficiency.

The effects of dissolved oxygen (DO) concentration combined with sublethal doses of ammonia on growth and food conversion efficiency (FCE) were investigated in juvenile spotted wolffish. Fish with a mean (S.D.) initial weight of 95.4 (18.0) g were reared in shallow raceways (initial stocking density 10 kg m −2 ) at normoxic (9.6 mg l −1 ) and hyperoxic (14.5 mg l −1 ) conditions, and also under both normoxia and hyperoxia with an additional sublethal concentration of unionised ammonia (0.17 mg NH 3 l −1 ) added, for 8 weeks at 8 °C. There was an interacting effect of oxygen saturation and ammonia level on growth, as growth rate was significantly higher in the hyperoxic/NH 3 group compared to the normoxic/NH 3 group ( P 2 consumption was significantly higher ( P 2 kg −1 h −1 ) compared to normoxic (79.9 mg O 2 kg −1 h −1 ) conditions. A clear diurnal rhythm in the O 2 consumption pattern was seen at both O 2 saturations, with the most striking observation being a dramatic increase in the morning when the light was turned on. Overall, our results support earlier findings of a high capacity to adapt to variations in environmental water quality parameters, and to restore normal growth rate in the spotted wolffish.

Growth performance and food conversion efficiency (FCE) were investigated in juvenile spotted wolffish (Anarhichas minor Olafsen), mean (S.D.) initial weight 15.7 (4.8) g, reared at four levels of carbon dioxide (CO2(aq)) for 10 weeks at 6 °C and 33‰. CO2 levels averaged 1.1 (control), 18.1 (low), 33.5 (medium) and 59.4 (high) mg l−1, with corresponding pH values of 8.10, 6.98, 6.71 and 6.45, respectively. In addition, kidneys from sampled fish were examined macroscopically for gross signs of calcareous deposits, i.e. nephrocalcinosis, at the start and end of the experiment. Growth was significantly reduced at the highest concentration (P

The atypical strains of Aeromonas salmonicida isolated from spotted wolffish Anarhichas minor O., show biochemical and molecular variations, but it is not known whether these variations affect bacterial virulence or antigenicity of possible protective antigens. In this study, protection against atypical furunculosis was compared in spotted wolffish vaccinated with monovalent or multivalent vaccines containing different strains of atypical A. salmonicida. In addition, these vaccines were compared to a vaccine containing an atypical A. salmonicida isolate from Atlantic halibut, Hippoglossus hippoglossus L. Vaccinated fish were challenged with three different A. salmonicida strains from spotted wolffish. Significant protection was obtained against both homologous and heterologous challenge. The best protection, regardless of strain used for challenge, was obtained with the multivalent vaccine composed of three different bacterial strains. Also, some of the monovalent vaccines resulted in significant protection, but they seemed to differ in protection against one particular strain of atypical A. salmonicida. In addition, significant cross-protection was observed with a vaccine containing a strain isolated from halibut, while a commercial salmon vaccine against furunculosis based on A. salmonicida subsp. salmonicida, failed to protect against an atypical strain from spotted wolffish.

Atypical furunculosis caused by atypical Aeromonas salmonicida is an increasing problem in commercial halibut farming, and a potential problem in farming of spotted wolffish in Norway. Halibut, Hippoglossus hippoglossus L., and spotted wolffish, Anarhichas minor L., vaccinated with oil-emulsified vaccines against atypical furunculosis, demonstrated a relative percent survival (RPS) of approximately 90 when challenged with homologous isolates. Bath and aqueous injection vaccines failed to protect against disease when challenged 10 weeks post-vaccination. High antibody titres were produced in both species after vaccination with oil-emulsified vaccines, and the major antibody response were against A-layer, LPS and some minor outer membrane (OM) proteins.

The reproductive biology and spawning behaviour of the common wolffish ( Anarhichas lupus ) was studied in the laboratory, and various facilities were tested in order to make common wolffish spawn in captivity. Fish caught on the south and west coast of Norway spawned between the middle of October and the middle of February, with a peak around the turn of the year. There is no sexual dimorphism in common wolffish prior to maturation. Towards spawning the ripening female adopts a pronounced pot-bellied shape. The testis is small, on average only 0.11% of the total body weight of males, and there is little difference in the size of running-ripe and non-running testes. At most 1.5 ml of milt was stripped from a running male, and males were found to be running during most of the spawning season. Running males have a papilla on their urogenital pore which may serve as a copulatory organ. Morphological as well as behavioural evidence strongly suggests that the eggs of the common wolffish are fertilized internally, and that copulation takes place 8–15 h before spawning. No successful, natural spawning took place in the various facilities tested, ranging from small tanks (4 m 2 ) with single pairs to big basins (up to 1500 m 2 ) with many wolffish present. The common wolffish seems to have a complex reproductive behaviour which probably makes it difficult to obtain natural spawning on a regular basis in captivity. Procedures are suggested for artificial fertilization of common wolffish eggs.