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Abstract The effects of temperature and growth hormone (GH) implantation on growth of juvenile Atlantic wolffish (Anarhichas lupus) were investigated. The year-long study had three sequential experimental phases (EP) termed EP1, EP2 and EP3, lasting for 6, 9 and 37 weeks, respectively. The experimental fish were divided into four groups and reared at different target temperatures (3, 7, 11 and 15 °C) during EP1 and EP2, but at a constant temperature of 7 °C during EP3. At the beginning of EP2, half of the fish from each group was implanted with formulation of recombinant bovine GH (Posilac®), while the other half was sham-implanted with vehicle. The optimal temperature for growth (T opt.G) of early juveniles (geometric mean weight 7.5 g) was determined as 12.1 °C during EP1, while the upper critical temperature (Tc) was concluded to be very close to 15 °C, as fish at that temperature had stunted growth, increased mortality and showed external signs of skeletal deformities. Thus, the species was found to be relatively stenothermic during the early juvenile stages and therefore vulnerable to relatively modest increases in environmental temperature above T opt.G. At 15 °C, GH implantation had no effects on growth rate. This indicates that the high allostatic load at this temperature leaves no scope for increased growth. In contrast, at lower rearing temperatures, the GH implantation had substantial, long-term effects on growth rate and induced remarkably similar relative growth stimulation at 3, 7 and 11 °C, suggesting a temperature-independent mechanism for the growth-promoting effects of GH. Highlights • The narrow span from optimal temperature for growth to upper thermal tolerance limits is notable and of concern. • GH treatment reveals significant growth potential and a temperature-independent growth-promotion mechanism. • Absence of growth stimulation at the upper thermal tolerance limits indicates a shift of energy use to vital functions. [ABSTRACT FROM AUTHOR]

Biological data were retrieved from 3694 female Atlantic wolffish Anarhichas lupus collected in Icelandic waters at four locations during the breeding season using a long–term study spanning from 2002 to 2013. The main objective was to investigate reproduction investment and timing. In the main spawning ground, little temporal differences were observed. In contrast, the peak of the spawning season was different among spawning grounds, suggesting spatial differences in the timing of reproduction. The size of females A. lupus was related to the spawning time with the larger fish spawning earlier than smaller ones. In addition, no significant pattern was found between temperature and spawning time. Except at its main spawning area where spawning begins in late September, spawning usually began in late August or beginning of September and was completed in early November. [ABSTRACT FROM AUTHOR]

Abstract: Growth rate is dependent upon adequate provision of amino acids especially in newly-hatched fish which experience very high growth rate. The replacement of a fraction of protein content by partially hydrolyzed (pre-digested) proteins was carried out and the digestive capacities and performances of larval/juvenile spotted wolffish (Anarhichas minor) were measured. The goal of this study was to verify whether the scope for growth is principally dictated by the proteolytic capacity of the digestive system by examining the effect of protein hydrolysates (PH) and trypsin inhibitor dietary inclusion on protein digestion/assimilation capacities, growth and survival. Four experimental diets were examined: C (control) I (supplemented with 750mg/kg soybean trypsin inhibitor (SBTI)) H (supplemented with 20% PH) and HI (supplemented with 20% PH and 750mg/kg SBTI). Protein hydrolysate supplementation gave significantly higher body mass than control at day 15 post-hatching. Unexpectedly, at day 30 and 60, fish administered diet HI (containing trypsin inhibitor) were heavier than the other groups. Suggested mechanisms are presented and discussed. The main conclusions of this study are that wolffish larval stage lasts roughly 15days and that juvenile growth is linked to proteolytic capacity, but also very likely to absorption capacity of peptides and amino acids. [Copyright &y& Elsevier]

Abstract: 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 (~10ng ml−1), whereas basal glucose levels were unusually low (0.3–0.4mM). After exposure to a short, but severe disturbance challenge (emptying the tank of water for 10min), the increase in plasma cortisol level was slow and relatively weak, reaching a peak level of 25ng ml−1 4 to 8h after disturbance. When the fish were exposed to a gradually decreasing oxygen level in the tank, a significantly elevated plasma cortisol level (35ng ml−1) was seen in the fish that remained in the tank until oxygen saturation had decreased to 20% oxygen saturation after 2.5h. However, a two-fold higher plasma cortisol level (~70ng ml−1) was seen in all fish exposed to reduced oxygen levels (60, 40 and 20% oxygen saturation) after 3.5h 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 ~170ng 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Tolerance, growth, ionic and osmotic response and gill enzymatic activity adjustments (Na+K+ATPase, COX, CS, PK and LDH) of Atlantic wolffish (Anarhichas lupus) exposed to different salinities (0‰, 7‰, 14‰, 21‰, 28‰ and 35‰) were examined. Direct transfer from seawater (SW) to freshwater (FW) of 0+ juveniles situated the L50 for salinity tolerance between 5‰ and 6‰. The data from prolonged exposure to various salinities indicate efficient homeostatic control in Atlantic wolffish A. lupus and improved growth performance at 14‰ compared to 28‰ after 70 days (calculated growth trajectories in length and in weight). The latter is linked to indications of reduced metabolic costs of ion regulation, i.e. significantly reduced Na+K+ATPase and LDH activity at 14‰ compared to 28‰ (Na+K+ATPase: 5.67±1.41 compared to 7.27±1.23 and 5.44±0.86 compared to 6.86±1.34 U/mg protein at weeks 14 and 19, respectively, p=0.05 and 0.026, respectively; LDH: 10.4±2.14 compared to 12.39±2.02 U/mg protein at week 14 and 12.46±1.34 compared to 17.17±2.67 U/mg protein for LDH, p=0.026 and 0.008, respectively). A strong positive relationship between Na+K+ATPase, LDH and PK activity was also observed [log y=1.107log LDH-0.914, p=0.0000, r2=0.46 (n=33) at weeks 14 and 19 and with PK (n=18) at week 19, log y=1.143 log PK-0.595, p=0.001, r2=0.497]. This indicates that from week 14 onward, the activity of branchial Na+K+ATPase is coupled to adjustments in the level of activity of the glycolytic enzymes. Our results indicate that Atlantic wolffish is a strong osmoregulator that demonstrates haloplasticity which enables cultivation of this species at reduced salinities with expected benefits in productivity. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

The presence of immunocompetent cells was studied in the larval and adult stages of the spotted wolffish, Anarhichas minor. In situ hybridization with a probe complementary to the secretory Igμ-chain was used to localize immunoglobulin producing cells or plasma cells in organs from adult fish and the appearance of these cells in lymphoid tissues during juvenile development. Plasma cells were located in pronephros, spleen, gut, gills and skin of adult wolffish. In juveniles, the first plasma cells were detected in the kidney 1 week post-hatching and the appearance in other lymphoid organs was in the order spleen, gut and thymus. No plasma cells were detected in skin and gills during the sampling period of juveniles (<10 cm). Our study confirmed that plasma cells are present in both the systemic and mucosal compartments of adult fish but during ontogeny there is an earlier appearance of plasma cells in the gut compared to gill and skin compartments. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]