This study describes the first successful rearing of capelin from hatch to adulthood in a laboratory setting using intensive culture methods. Over the span of about two years, the capelin were reared in aquaculture tanks under a constant temperature of 7 °C. The capelin demonstrated a robust linear growth during their first year of life, with a mean length increment of 0.36 mm per day. Due to their accelerated growth, some of the capelin became sexually mature as early as one year post-hatch. The first year was characterized by a rapid increase in condition factor (CF) while the second year showed a plateau. The von Bertalanffy growth equation effectively described the two-year growth of the cultivated capelin, predicting an asymptotic length (L∞) of 18.4 cm, similar to the 18.6 cm median L∞ of wild Icelandic capelin (1981–2018 cohorts). The cultivated capelin were projected to reach this length in 2.6 years, compared to about 6 years for wild capelin. This study provides new insights into the growth dynamics of capelin and although the species is sensitive to handling, it demonstrates that intensive culture methods can be used to investigate biological aspects of this important forage species.

The effects of early thermal environment on growth, age at maturity, and sexual size dimorphism in Arctic charr (Salvelinus alpinus) are investigated. This study is a 654-day long rearing trial split into two sequential experimental phases termed EP1 and EP2 and lasting 315 and 339 days, respectively. EP1 started at the end of the yolk sac stage when the experimental fish were divided into three groups and reared at different target temperatures (7, 10 and 12 °C). During EP2, all groups were reared at the same temperature (7–8 °C) until harvest (~1300 g). Growth rates increased with temperature from 7 to 12 °C, and at the end of EP1 the 12C group had 49.0% and 19.2% higher mean weight than groups 7C and 10C, respectively. Elevated early rearing temperatures were, however, found to cause precocious sexual maturation and reduce the long-term growth performance. At the end of EP2, the 7C group had 3.6% and 14.1% higher mean weight than 10C and 12C, respectively. Elevated early rearing temperatures had a much stronger effect on the maturity incidence of females, and while male-biased sexual size dimorphism (SSD) was found in all groups, the magnitude of SSD was positively associated with temperature.

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 (Topt.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 Topt.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.

To study the isolated and combined effects of unionised ammonia (UIA-N) and CO2 in water on juvenile Atlantic cod, fish were exposed to four different treatments: moderate levels of CO2 (10mgL−1); moderate levels of NH3 (0.06mgL−1 UIA-N); a combination of CO2 (10mgL−1) and NH3 (0.06mgL−1 UIAN) and a control treatment without added CO2 or NH3, for 41days. The final weight of the groups exposed to either CO2 or NH3 were not significantly different from the control group, where 22% weight gain was observed during the course of the 41-day exposure time. Minor differences in SGR were observed during the first growth period, but not later, between the control and the CO2 and NH3 groups, suggest that the fish were able to adapt to the conditions over time. However, no weight gain and lower feed intake was observed in the group exposed to both CO2 and NH3. To create identical [UIA-N] for the NH3 and CO2+NH3 groups it was necessary to double the [TAN] for the latter group due to lower pH resulting in doubling of [NH4+]. It is suggested, that the high [NH4+] to which the CO2+NH3 group was exposed may have caused the reduced growth.

In land-based fish farms, water quality can be controlled to support maximum growth and good feed conversion. Oxygen is an important water quality parameter in aquaculture and the objective of this study was to detect the range of oxygen saturations that maximizes growth of juvenile Atlantic cod. The fish (initial body mass 21.9g) were reared at five different levels of oxygen saturation: 65%, 81%, 103%, 121% and 150% of air saturation, for 98days. At oxygen saturation under 100%, the growth of the fish decreased linearly with progressively lower oxygen saturation with the final body mass of fish reared at 65% saturation being 24% lower than that of fish reared at 103% saturation. The final body mass of fish reared at 150% saturation was significantly higher (7%) than that of fish reared at 103% saturation. Feed intake was also affected by oxygen saturation and was proportional to growth while the feed conversion ratio was not significantly affected by oxygen levels. The results suggest that oxygen saturation of at least 100% is required to obtain maximum growth of juvenile Atlantic cod.

High larval mortalities and anatomical deformities are among the major obstacles restricting the development of Atlantic cod (Gadus morhua) aquaculture. The immune system of cod larvae is poorly developed at hatch, and innate immune parameters are therefore of importance for defence against environmental microorganisms. Two separate experiments were conducted with bioencapsulation of the live feed of cod larvae using a pollock (Pollachius virens) protein hydrolysate. Offering peptide enhanced live feed to larvae during the first weeks of exogenous feeding promoted larval development, with reduced incidence of severe deformities to 3.0% as compared with 9.6% deformities observed in the control group at 160 days posthatch. The production and distribution of IgM and lysozyme were furthermore increased in larvae fed peptide enhanced feed compared with control larvae. IgM was predominantly detected in the foregut and the epithelial lining of the digestive tract as well as in the epidermal mucus of the skin. Lysozyme was mainly detected in the epidermal mucus of the skin and in the foregut. Overall, the results indicate that live feed enhancement using a protein hydrolysate derived from pollock may reduce deformities and promote normal development during early production stages of cod larvae.

Induction of triploidy has been suggested as an effective tool to prevent spawning of farmed fish. This experiment examined the growth potential of triploid cod when reared communally with diploid ones after the juvenile stage. Pressure treatment was used to induce triploidy in a batch of cod eggs in April 2009. The resulting offspring were reared separately from their diploid counterparts until they reached the proper size for PIT tagging. At the age of 8 months, an equal number of 115 diploids (135.5 ± 3.95 g) and triploids (93.6 ± 2.63 g) were communally reared in a circular flow-through tank until the age of 22 months. By the end of this rearing period, diploids (1,002.4 ± 39.9 g) were significantly heavier than triploids (654.6 ± 27.7 g), but the specific growth rate did not differ significantly during the growth trial. Gonadal development at the age of 22 months was also lower among triploids than diploids, especially for females (5.3 and 91.9 %) but also for males (32.5 and 72.7 %). Sterility among female triploids was evident by the reduced size and dysfunctional gonads, but gonadal development in male triploids was less suppressed. Prevalence of body deformities was, however, significantly higher among triploids (62.6 %) than diploids (33.9 %). Higher prevalence of deformities in triploid cod underlines the need for further fine-tuning of the triploidization procedure or finding other methods of sterilization. At present, triploid cod are still far from being established as an alternative for commercial production.

The effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters were investigated in two experiments. In the first experiment small, medium and large juvenile Atlantic cod Gadus morhua (initial average weights of 1.9, 8 and 83g, respectively) were reared at four constant salinities (6 to 32‰) for a short period (19–57days, depending on size), then returned to seawater (32‰) without acclimation and reared for another period (20–391days). The highest growth rates were found at 10‰ in all size-classes. After the fish were returned to seawater the growth rates were inversely related to the salinity change in all size-classes and long-term rearing of the medium-sized fish revealed that abrupt salinity increase from 6 and 10‰ to seawater may permanently reduce the growth capacity of juvenile cod. In another long-term experiment, there was no significant difference in the growth rate of cod (initial average weight 3.4g) reared at either 13.5 or 32‰ for 187days. Rearing at 13.5‰ neither enhanced growth rate at 6.3°C nor at 10°C in larger juveniles (>245g) compared with rearing in seawater. The study shows that rearing salinity and abrupt salinity changes have limited or no effects on stress and immune-related parameters, and there are no indications of ion regulatory disturbances at salinities as low as 6‰. This shows that the Atlantic cod is an extremely euryhaline marine teleost species, and indicates that commercial Atlantic cod aquaculture can just as well be carried out in locations with low as with high environmental salinity.

The effects of stocking density on the productivity in a juvenile cod farm were studied in a flow-through system for fish weighing initially 44g. The fish densities increased throughout the experiment from 4 to 21, 11 to 54 and 22 to 95kg/m3. Growth rates were negatively affected at densities above 50kg/m3 and at the end of the experiment the mean weights were 242, 221 and 205g at low, medium and high densities, respectively. The average cumulative mortalities increased with density and were 1.8, 4.2 and 7.3% of initial number of fish at low, medium and high densities, respectively. Antibiotics were administered twice at high, once at medium and never at low density. The average feed conversion ratios were 0.81, 0.91 and 1.02 at low, medium and high densities, respectively. The average biomass increase was 16.8, 42.7 and 72.8kg/m3 at low, medium and high densities. A simple economic analysis indicates a parabolic relationship between profit and density with optimal density at the peak of the curve. Given reasonable assumptions about production costs in a land-based farm, the break-even density is 35kg/m3 and the optimal final density is 95kg/m3. Changes in fixed costs, such as financial costs and salaries, have no effects on the optimal final density whereas changes in variable costs, such as feed and juvenile costs, directly affect the optimal final density.

Cathelicidin antimicrobial peptides are multifunctional peptides that are important in the innate immune system of mammals. Cathelicidins have been identified in several fish species. In this study we have isolated cathelicidin from Atlantic cod (Gadus morhua) and identified the cleavage site from the cathelin propart. This is the first isolation of a cathelicidin from teleost fish. The mature cathelicidin was found to be a 67-residues peptide, highly cationic with a pI of 13. Reversed phase chromatographic fractions containing the purified peptide had pronounced antimicrobial activity and the activity of the mature peptide was confirmed using a synthetic peptide. We examined the expression of cathelicidin during cod larvae early development using real-time PCR and detected expression that varied in the course of the first 68 days post hatching (dph). Two groups of larvae having a different food regime were compared. Cathelicidin expression was found to differ between the two groups and this could be linked to their food input. The presence and rapid adjustment of cathelicidin expression in the larvae indicate that the immune system of cod is active from early on in development and responds to external stimuli by the production of antimicrobial peptides.

An intervention study was conducted at early juvenile stage of Atlantic cod (Gadus morhua L.) rearing to confirm the properties of two prospective probionts, Arthrobacter sp. and Enterococcus sp. isolated from a cod hatchery. Juveniles (10g) were fed expanded dry feed for 28 or 55days, either untreated or treated with the probiotic bacteria in mixture or singly (107–9CFUg−1 feed). Viability of probionts supplemented to the feed was evaluated during a two-month storage at −20, 4 and 15°C and sensory evaluation of the probiotic feed performed at the end of storage. Juvenile growth, survival, feed conversion ratio, and microbial load of rearing water, juvenile gills and gut were examined. Microbiological stability of the probionts added to the feed was demonstrated at all temperatures, while sensory evaluation detected faint oxidative off-odours in feed stored frozen. Juveniles fed the Enterococcus-probiotic feed grew significantly faster and had significantly lower gut Vibrio counts than control juveniles (p<0.05). Overall, the results suggest that both probionts, especially the Enterococcus strain, modified the gut microbiota and contributed to enhanced juvenile growth and survival.

Stable supplies of high quality cod larvae and juveniles are urgently needed for the development of successful cod farming industries in countries around the North Atlantic. The project is a collab ...

This work aimed at validating the use of two prospective probionts (Arthrobacter sp. and Enterococcus sp.) at early stages of cod (Gadus morhua L.) rearing. Ova at late post-fertilized stage and larvae during their first 4 weeks of life were bathed with both probionts, isolated previously from the cod-rearing environment. This treatment was compared with groups fed rotifers supplemented with a commercial probiotic (Remus (R)) and those untreated. Microbiological analyses (total viable counts, presumptive Vibrio and lactic acid bacteria) were performed in rearing systems and larval survival, growth and development were assessed. Larval development was evaluated by proteolytic activity of larval lysates and immunological analysis of important proteins: apolipoprotein A-I, haemoglobin, C-reactive protein, C3 and cod serum proteins. Bacterial bathing led to a significantly higher larval weight, length and culturable microbial load in larval gastrointestinal (GI) tract when compared with the control and Remus groups. Development occurred earlier in bathed larvae. However, their survival was negatively affected compared with the control group, but was significantly higher than for the Remus group. The non-pathogenicity of both probionts was demonstrated by intraperitoneal injection of 13 g cod juveniles. The results suggest that Arthrobacter and Enterococcus probionts affected the larval GI microbiota and contributed to growth, development and digestion, either directly or indirectly.

Phenotypic plasticity and local adaptations are important considerations in delineating population structure of marine fishes and critical to their conservation and management. We compared the weight-specific oxygen consumption rates (VO2/M) of juvenile cod from the northern and southern components of the Icelandic stock acclimated to 4.0°C, 8.5°C, and 12.6°C and their metabolic response to abrupt temperatures changes within this range. Southern individuals exhibited VO2/M up to 50% higher than their northern counterparts when tested at their acclimation temperature. However, northern fish generally experienced greater changes in VO2/M, three to six-fold increases, relative to that expected at acclimation when moved to higher temperatures. Southern cod showed a greater decrease in VO2/M when exposed to lower temperatures. Our results indicate physiological differences exist between the northern and southern components of the Icelandic cod stock and warrant considering them as two distinct populations.

Six size groups of hatchery produced turbot (2–499 g) were reared at six constant temperatures (10–25 °C). The results were used to develop a mathematical model for growth rate and feed conversion in turbot. At each temperature there were linear relationships between logarithms of (a) specific growth rate (G%/day) and body weight (W g), and (b) feed conversion ratio (FCR) and W. The slopes of the regressions were linearly related to temperature and the intercepts of the regression changed with temperature according to a second order polynomial. The optimal temperature for growth (Topt.G) is predicted to decline with increasing body weight: Topt.G = 22.45 − 0.713lnW, i.e. 22.5, 20.8, 19.1 and 17.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the growth rates of these fish sizes at their optimal temperature (Gmax) were predicted to be 7.63, 2.73, 1.03 and 0.40%/day, respectively. The optimal temperature for feed conversion (Topt.FCR) is also predicted to decline with increasing fish size: Topt.FCR = 18.80 − 0.625lnW, i.e. 18.8, 17.4, 15.9 and 14.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the predicted feed conversions of these fish sizes (FCRmin) were 0.44, 0.56, 0.68 and 0.82 for the present feed types. The growth model predicts that 2 g turbot can reach 743 and 619 g in 1 year when reared at Topt.G and Topt.FCR, respectively.