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Simple Summary Spotted wolffish, a cold-water fish species, is a high potential candidate marine fish species for the diversification of the aquaculture sector in Norway, Canada, and Iceland. A review of the state of advancement of all aspects of its reproduction is proposed. Species-specific life-history and reproduction traits are discussed in parallel with relevant information originating from past R&D activities and the current state of knowledge regarding rearing environmental conditions and practices possibly affecting broodstock performances. Abstract The first artificially fertilized spotted wolffish (Anarhichas minor) eggs hatched in Norway in the mid-1990s as this species was considered by Norwegian authorities to be a top candidate species for cold-water aquaculture in the North Atlantic regions. Previous research conducted in Norway (since 1992) and Canada (since 2000), focused on identifying key biological parameters for spotted wolffish cultivation which led, respectively, to the rapid establishment of a full commercial production line in northern Norway, while Québec (Canada) is witnessing its first privately driven initiative to establish commercial production of spotted wolffish on its territory. The control of reproduction can be viewed as a major requirement to achieve the development of performant strains using genetic selection tools and/or all-year-round production to bring about maximal productivity and synchronization among a given captive population. Although the basic reproduction aspects are more understood and controlled there are still some challenges remaining involving broodstock and upscaling of operations that limit the achievement of a standardized production at the commercial level. Quality of gametes is still considered a major constraint and it can be affected by multiple factors including nutrition, environmental conditions, handling practices, and welfare status. Internal insemination/fertilization and the protracted incubation period are challenging as well as the establishment of a health monitoring program to secure large-scale operations. The profound progress achieved in the control of reproduction, sperm handling, and cryopreservation methods for this species is presented and discussed. In this review, we also go into detail over the full range of up-to-date cultivation practices involving broodstock and identify areas that could benefit from additional research efforts (i.e., broodstock nutrition, health and welfare, scaling-up egg and larval production, genetics, and development of selective breeding programs).

Sexual size dimorphism (SSD) in wolffishes has never been unquestionably reported in previous fisheries or aquaculture studies. The sex-related growth patterns of 6+Anarhichas lupus and 3+A. minor (Norway (NW) and Quebec (QC) populations) were monitored in replicates in a controlled environment over two successive spawning seasons (21 months). Overall growth achieved indicates the expression of male-biased SSD in males of A. lupus, A. minorqc and A. minornw, being 36.2, 34.0 and 19.6% heavier and 9.7 ± 0.3%, 5.8 ± 0.4% and 5.4 ± 0.2% longer respectively. Male and females A. minor of both populations started at 1 kg body weight and males ended up averaging 3.2–3.5 kg. Females from Norway and Canada reached 2 kg and 2.8 kg respectively, indicating a male growth advantage over female and a lessened expression of SSD in the Norwegian population. A. minornw achieved higher final weight and length in comparison to A. minorqc. In captivity, females underwent normal maturation cycles whereas males were free from egg-guarding duties, which most likely contributed to the expression of SSD benefiting males. In the wild, prolonged embryo paternal care duties, coupled with loss of teeth and reduced feeding during incubation, likely offset any substantial growth advantages for males. The observed reduction in female growth and condition factor values coincide consistently with maturation events. Female specific growth rate also showed more pronounced fluctuations, leading to the observation of a significant growth divergence. The sex-specific growth trajectories achieved in captivity are briefly compared with observations from fishery-based growth studies that not once reported conclusive sex differences. Our observations point to the behavioural and environmental sensitivity of SSD and to the rationale of sex control in wolffish cultivation to produce all male stocks and only rear the fastest-growing sex.

This study provides new and practical information to implement the use of photoperiodic manipulation for the control of the sexual maturation of Canadian 6+ Atlantic wolffish (Anarhichas lupus) and 3+ first-time spawners spotted wolffish (Anarhichas minor) from Canadian and Norwegian populations. Wolffish reproductive cycle (gametogenesis and oocyte maturation and spermiation) was monitored for 23 consecutive months. Control groups were held under a 12-month simulated natural photoperiod and treatment groups under an 8-month compressed photoperiod. Plasma sex steroid concentrations (estradiol-17β and 11-ketotestosterone), oocyte diameter growth, and milt production were assessed monthly. For all groups under study, fish subjected to the compressed photoperiod spawned 2–6 months earlier than the controls. Complete out-of-shift cycle was not achieved based on the completion of two reproduction cycles, and this is briefly discussed. Photoperiod treatment induced temporal shifts in sex steroid profiles, which are the likely mediators of altered timing of ovulation/final maturation. Photoperiod has a strong influence on the timing of wolffish maturation and could be used as an efficient and inexpensive tool to secure wolffish reproduction operations (year-round supply of egg and milt and/or timing with optimal temperature regimes).

Hybridization between closely related species can generate genetic and phenotypic variation, providing valuable biological material to assess the physiological impact of the structural or functional variability of different organs. In the present study, we examined growth rates of various organs and whole body in brook char, Arctic char and their reciprocal hybrids over a period of 281 days. Parental species achieved significantly higher body mass than their hybrids. Hybridization significantly reduced the relative size of the heart, liver and spleen. The relative size of pyloric caeca did not differ among the four groups. The observed lower growth performance of the hybrids compared to parental species strongly suggests that divergence in the relative size of digestive organs, liver and heart partly dictate growth capacity. Our results also suggest that the increased variability achieved through hybridization may prove useful in a genetic selection program., Summary: This research provides a comprehensive overview of the phenotypic modifications in growth trajectories of body size and internal organs following interspecific hybridization in chars.

The purpose of this study was to determine the cortisol response of spotted wolffish (Anarhichas minor) after exposure to air immersion and netting (acute stress) under a range of increasing densities (chronic stressor). In addition, the presence of a cumulative negative impact from chronic stress was assessed by the application of an additional acute stressor following rearing at various densities, and proxies of behavior were evaluated (feeding and aggression data). The stress response to air immersion and netting led to increasing plasma cortisol values at 0.5, 13, and 37 h post-stress, with the highest value achieved after 13 h. At 168 h, cortisol concentrations returned to similar pre-stress value. Changes in cortisol concentrations were relatively low after acute stress (five to six fold increases) and recovery time long lasting (>37 h). Prolonged rearing at 20, 30, and 40 kg m−2 showed a non-significant trend of increasing cortisol values with increasing density, and the cortisol response after the...

Cellular and mitochondrial metabolic capacity of the heart has been suggested to limit performance of fish at warm temperatures. We investigated this hypothesis by studying the effects of acute temperature increases (16, 23, 30, 32.5 and 36°C) on the thermal sensitivity of 10 key enzymes governing cardiac oxidative and glycolytic metabolism in two populations of European perch (Perca fluviatilis) field-acclimated to 15.5 and 22.5°C, as well as the effects of acclimation on cardiac lipid composition. In both populations of perch, the activity of glycolytic (pyruvate kinase and lactate dehydrogenase) and tricarboxylic acid cycle (pyruvate dehydrogenase and citrate synthase) enzymes increased with acute warming. However, at temperatures exceeding 30°C, a drastic thermally-induced decline in citrate synthase activity was observed in the cold- and warm-acclimated populations respectively, indicating a bottleneck for producing the reducing equivalents required for oxidative phosphorylation. Yet, the increase in aspartate aminotransferase and malate dehydrogenase activities occurring in both populations at temperatures exceeding 30°C, suggests that the malate-aspartate shuttle may aid to maintain cardiac oxidative capacities at high temperatures. Warm acclimation resulted in a reorganization of the lipid profile, a general depression of enzymatic activity and an increased fatty acid metabolism and oxidative capacity. While these compensatory mechanisms may contribute to maintain cardiac energy production at high temperatures, the activity of the electron transport system enzymes, such as complexes I and IV, declined at 36°C in both populations indicating a thermal limit of oxidative phosphorylation capacity in the heart of European perch.

Vitellogenin (VTG) from spotted wolffish, Anarhichas minor, a candidate species for cold-water marine aquaculture, was purified by MgCl2/EDTA precipitation followed by a two-step chromatographic procedure. VTG had an apparent molecular mass of 470 kDa, as determined by gel filtration, and an amino acid composition similar to those of other teleosts. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the purified VTG revealed a major band with a relative molecular weight of 166 kDa and some minor bands. Spotted wolffish VTG (sw-VTG) is relatively robust to in vitro degradation, as shown when samples of purified VTG and plasma from mature females subjected to various storage conditions or multiple freeze/thaw cycles were analyzed by Western blot. We developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) using an antibody against Atlantic wolffish (Anarhichas lupus) VTG and purified sw-VTG. The ELISA had a detection limit of 6.7 ng/ml and a working range of 16.2–787.5 ng/ml, with intra- and inter-assay coefficients of variation ranging from 1.5 to 7.3 % and 7.1 to 14.3 %, respectively. The assay could distinguish males from immature females and discriminate maturing females at different stage of oocyte development. These results suggest that the sw-VTG ELISA would be useful in spotted wolffish aquaculture to determine sex and monitor female maturation.