Search

In this study, we explored the effects of chronic stress on lumpfish (Cyclopterus lumpus) physiological, immune response, health, and plasma free amino acids. 3 groups of lumpfish were exposed to 1-minute air exposure. 1 group was exposed to stress once per week, a second group exposed 2 times per week, and a third group exposed 4 times per week. The present study revealed significant alterations in immunity and increased nutritional demands, particularly the branched chain amino acids and lysine. Cortisol levels fluctuated, with significantly higher levels halfway through the experiment on the groups that were stressed more often. Though, by the end of the experiment, there were no significant differences in cortisol levels between groups. Regardless of stress exposure, cataract developed in virtually all sampled fish, pointing toward a potential dietary imbalance. A transient immunomodulation of stress was visible. While in early stages stress had an immune enhancing effect, as seen by the increase in plasma nitric oxide and peroxidase in the group most frequently exposed to stress, these differences were not apparent by the end of the experiment. Additionally, the worst health condition was found in this group. Our results underscore the complex interplay between stress, immunity and nutrition, highlighting the need for tailored dietary strategies and improved rearing practices. [ABSTRACT FROM AUTHOR]

Simple Summary: Farmed fish are commonly exposed to stressors, which have a detrimental effect on their health and welfare. The present study explores how lumpfish, a species recognized for its potential role in alleviating the sea lice burden on farmed salmon, responds to acute stress. This is particularly important for this species, since there are concerning reports regarding their health and welfare. In our stress challenge lumpfish were exposed to air for one minute. We then examined several stress and energy metabolism biomarkers and concluded that i) lumpfish tolerates well a one-minute air exposure, and ii) cortisol is a reliable stress biomarker in this species. Our results contribute to our current understanding of how lumpfish handle a common stressor, and this knowledge is key to allow a better decision-making when it comes to welfare management in farms. This study aimed to expand knowledge on lumpfish stress physiology by investigating the effects of acute stress on primary (i.e., cortisol) and secondary (e.g., metabolites) stress responses, as well as oxidative stress biomarkers, from stress exposure to a recovery phase. The results showed that the lumpfish physiological response to 1 min air exposure is mild, in line with recent studies, and comparable to that described for white sturgeons. Cortisol seems to be the most reliable acute stress biomarker in lumpfish, with a significant increase in plasma 30 min after stress exposure, returning to resting levels 2 h after exposure. In contrast, glucose and lactate were not significantly altered by short-term air exposure. Effects on hepatic energy mobilisation were also detected following the acute stress. This study showed that acute 1 min air exposure seems tolerable, allowing a swift recovery. However, more studies on the impacts of air exposure and repeated acute stressors on lumpfish stress and immune responses are required to develop industry standards for lumpfish health and welfare monitoring. [ABSTRACT FROM AUTHOR]

Environmental challenges related to open sea cage production of Atlantic salmon have sparked interest in developing commercial-scale semi-closed sea systems for post-smolt Atlantic salmon (100–1000 g). Determining the mass-specific water flow required by post-smolts will largely influence the design and dimensioning of such systems. In this experiment, post-smolts were exposed to four levels of specific water flow: 0.2, 0.3, 0.4, and 0.5 L kg fish−1 min−1. All treatments involved flow-through seawater with full oxygenation, a salinity of 34‰, and a mean temperature of 9.3 °C. The stocking density was kept stable at 75 kg m−3. Water pH decreased with reduced flow, while partial pressure of carbon dioxide (pCO2) and total ammonia nitrogen (TAN) in the water increased. The increase in water CO2 was reflected in the blood with increased pCO2, HCO3−, and decreased Cl− in the lowest water flow treatment (0.2 L kg fish−1 min−1), indicating a typical regulatory response to increased water CO2 over the eight-week experimental period. No negative effects on osmoregulation, external macroscopic welfare, or performance indicators were observed, suggesting that within the time period of this experiment, post-smolts can compensate for reductions in water flow down to 0.2 L kg fish−1 min−1. However, to avoid activating and exhausting potentially energy-costly physiological regulatory mechanisms, it is suggested to keep specific water flow above 0.3 L kg fish−1 min−1 in large-scale operations with semi-closed sea systems at intermediate temperatures. [ABSTRACT FROM AUTHOR]

Lumpfish are widely used for removing sea lice in salmonid sea-based aquaculture. If these fish are to be harvested and used for human consumption, it is necessary to know how the physical strain associated with removing the lumpfish from the net-cages affects the fish in the short-term, and if live-storage in tanks, well-boats, or nets awaiting slaughter, will result in stress and mortalities. In this study, we investigated the effect of physical stress and mortality in a group of lumpfish recaptured from commercial net-cages, transported to holding tanks, and stored for one week. In addition to cortisol (primary stress response), we analyzed ions directly related to osmoregulation (Na+ and Cl−), osmotic stress (Ca2+), and blood plasma pH as an indicator of a secondary stress response. The aim of the study was to increase the basic physiological understanding of the physiological effects of handling procedures and transport in lumpfish. Only minor, and temporary, effects on primary stress response and secondary stress response were seen in lumpfish recaptured from net-cages and transported to holding facilities, indicating that lumpfish cope well with short transport (here 5 h). These findings are important in a context where lumpfish are harvested for reuse, e.g., human consumption or processing, following their lice-eating stage in net-cages. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of alternating feeding (Alt) compared with control being fed every day (Con) in the on‐growth face of Atlantic cod. Individually marked fish (198 and 98 in the Con and Alt groups, respectively) was sampled for weight and length on 6 occasions over a 15‐month period, where mean weight increased from 628 and 758 g to 2635 and 3041 g, for the Con and Alt groups, respectively. Feeding alternate day resulted in 13 percentage more weight gain in the alternating feeding group (2283 vs. 2007 g) and improved feed conversion ratio (FCR, 1.07) compared with control (FCR 1.45). The Alt group consumed significantly less feed (27%) compared with control. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days during the on‐growing period of Atlantic cod. [ABSTRACT FROM AUTHOR]

Currently, no information is available on the effect of progressively decreasing temperatures on the sensory quality of Arctic charr. The objective of this study was to investigate if and how different and progressively changing rearing temperatures affect the sensory quality of cooked and raw fillets of Arctic charr. The effects of rearing temperature on the sensory quality of Arctic charr (weight range 622–888 g) were investigated. Rearing temperature was changed during the experimental period as the fish were reared at constant or decreased temperature during October to April and subsequently reared at two constant temperatures from April to August establishing six different rearing temperature combinations. Significant differences were seen in all four main sensory attributes groups, that is odour, appearance, flavour and texture. Freshness characteristics such as sweet odour and flavour, and metallic odour and flavour increased with decreasing rearing temperature, whereas musty odour and flavour decreased. Rearing temperature had a clear effect on the colour of the fillets. Lower rearing temperature increased colour intensity substantially. Softness, juiciness and tenderness increased with decreased rearing temperature. A trend was seen towards more effect from final rearing temperature than initial temperature on the sensory attributes studied. Spoilage characteristics, that is, sour and rancid odour and flavour, and off‐odour and flavour were either very weak or not noticeable in all sample groups. [ABSTRACT FROM AUTHOR]

In this mini review, we systematized current knowledge about the number of Caligus elongatus on farmed Atlantic salmon in relation to the use of lumpfish as cleaner fish. The review was prompted by reports of an unusually large number of sea lice (C. elongatus) infestation of farmed salmon in northern Norway, Faroese Islands and Iceland and the urgent need to determine if common lumpfish can be used to reduce the number on farmed Atlantic salmon by actively grazing on sea lice. Available data from Norway clearly indicate that lumpfish grazes on C. elongatus, and it is possible to enhance this grazing with the assistances of live-feed conditioning prior to sea pen transfer and selective breeding. Observations from Iceland, Faroese Islands and Scotland also indicate that lumpfish can effectively lower infestations of C. elongatus on salmon. Overall, this mini review expresses that lumpfish can actively lower the number of C. elongatus on farmed Atlantic salmon. [ABSTRACT FROM AUTHOR]

The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming. [ABSTRACT FROM AUTHOR]

Possible interactive effects of temperature and photoperiod on flesh quality in Atlantic salmon post‐smolts were studied. Juvenile (initial mean weight 96.0 g ± 3.1 SEM) Atlantic salmon were reared at six different combinations of temperatures (4.3, 6.5 or 9.3°C) and photoperiods (continuous light or simulated natural photoperiod). At termination of the trial, the fish were slaughtered and flesh samples taken to investigate quality and textural properties in the different experimental groups. Final weight in the six experimental groups varied between 174 and 345 g. Softer texture was seen in the fast growing groups. Photoperiod has only minor effect on flesh quality and textural properties, whereas temperature had significant impact on most of the measured variables. Although positive for growth, higher temperatures might be less favourable in relation to softer muscle tissue. [ABSTRACT FROM AUTHOR]

This study assessed the use of different types of substrates (450 g PVC, 130 g plastic) and water speed (5.0, 10 and 20 cm s−1) on growth and substrate selection in lumpfish. There were no differences between the percentages of fish attached to both types of substrates as they grew for each of the three different water speeds. Substrate adherence was similar on both substrate types and for all water current speed as the study progressed and was between 25 to 30% in all groups at termination of the trial. Results from the present study show that increasing water speed did not affect attachment preferences in lumpfish as they grew. Larger specimens were observed attaching to both thin and thicker substrates equally. Water speed did not affect growth performance as there were no differences in growth observed at the end of the study period between the three groups of lumpfish. However, further studies are required to determine if higher water speeds affect both growth and attachment preference of lumpfish as they grow. [ABSTRACT FROM AUTHOR]

Abstract: Three duplicate groups of individually tagged lumpfish (mean initial weight: 20.0 ± 4.0 g) were fed three commercially available diets (A, B and C) for a period of 147 days. There were significant differences in growth rates between the groups with fish fed diet A having the highest growth rates whilst fish fed diet C achieved the lowest growth. Lumpfish fed diets A and B had lower prevalence and severity of cataracts compared with fish fed diet C, suggesting a possible dietary effect on cataract, alone or in combination with other environmental factors. There was a significant difference in the degree of liver vacuolization between the three dietary treatments at the end of the study period with fish fed diets A and B showing moderate to severe vacuolization compared with liver tissue from fish fed diet C, which had milder vacuolizations. There was little or no inflammation in pyloric caeca, midgut and hindgut and similarly for epithelial necrosis or vacuolization for all three dietary treatments at the end of the study. Fish fed diet A had the longest intestinal folds whilst fish fed diet C had the shortest. [ABSTRACT FROM AUTHOR]

Abstract: Efficient sea‐lice control remains one of the most important challenges for the salmon farming industry. The use of wrasse (Labridae) as cleaner fish offers an alternative to medicines for sea‐lice control, but wrasse tend to become inactive in winter. Lumpfish (Cyclopterus lumpus) continue to feed on sea‐lice at low temperatures, and commercial production has escalated from thousands of fish in 2010 to well over 30 million juveniles deployed in 2016. However, production still relies on the capture of wild broodstock, which may not be sustainable. To meet global industry needs, lumpfish production needs to increase to reach c. 50 million fish annually and this can only come from aquaculture. We review current production methods and the use of lumpfish in sea cages and identify some of the main challenges and bottlenecks facing lumpfish intensification. Our gap analysis indicates that the areas in most need of research include better control of maturation for year‐round production; formulation of appropriate diets; artificial selection of elite lines with desirable traits; and development of vaccines for certified, disease‐free juvenile production. The welfare of farmed lumpfish also needs to be better quantified, and more information is needed on optimal densities and tank design. Finally, the risk of farmed lumpfish escaping from net pens needs to be critically assessed, and we argue that it might be beneficial to recover cleaner fish from salmon cages after the production cycle, perhaps using them as broodstock, for export to the Asian food markets or for the production of animal feeds. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this project was to investigate if lumpfish can be fed using specially designed feed blocks instead of regular fish feed pellets. Two studies were performed. In Part I different designs of feed blocks were introduced and fish observed with underwater cameras to record feeding behaviour. Results indicate that lumpfish require feed blocks with grooves in order to graze from them and that the acclimation period is relatively short (2–4 hr) before the fish will use them as a feed source. In the second part of the project two duplicate groups of lumpfish with an initial mean (±SD) weight of 125.4 ± 45.7 g were individually weighed and randomly distributed into six 3.5 m3 circular flow‐through tanks with 45 fish in each tank. Fish in three tanks were fed using feed blocks with grooves and fish in three tanks were fed using a regular commercially available lumpfish extruded feed. Both groups received a daily feeding rate of 2% body/weight. From day 14 onwards, fish fed with marine pelleted feed had a significantly higher mean weight compared to fish fed with feed blocks. Although not significant, the condition factor was higher in the feed block group during the study period. Results from this study show that lumpfish will readily graze from feed blocks if they are presented in a way that allows them to do. In addition, the acclimation period required before the fish will utilize them appears to be short thus potentially allowing for their use in commercial salmon cages. [ABSTRACT FROM AUTHOR]

Different levels of pressure were investigated to see if it was possible to induce triploidy at a lower pressure than previously used (600 bar) for Atlantic cod (Gadus morhua). Newly fertilized eggs were exposed to different levels of pressure: 400, 500, and 600 bar, and one control group (no pressure). Induction of triploidy occurred at each pressure level used in this experiment. Mean weight and length at the termination of the trial period was significantly lower, in the 400 bar group, compared to the other treatment groups. Microsatellite loci analysis revealed over 90% triploid outcome in each experimental group. Lower incidence of deformities was seen in the 400 bar group compared to the 500 and 600 bar groups. Overall this study demonstrated successful triploid induction at both low (400 bar) and medium (500 bar) pressures. [ABSTRACT FROM AUTHOR]

Atlantic cod Gadus morhua L. (initial weight 130 g, final weight 2800 g) was exposed to continuous light at different stages during the production cycle, and the effect on growth performance, age at first maturation, plasma sex steroid levels and flesh quality were investigated. The entire photoperiod experiment was divided into five phases where the fish in each phase were exposed to either natural photoperiod (N, 65°28′) or continuous light (C). Thus, the following five photoperiod combinations were tested: (a) control group ( NNNNN), (b) group 2A ( NCNNN), (c) group 2B ( NNCNN), (d) group 2C ( NNNCN) and (e) continuous light group ( CCCCC). Short-term exposure to continuous light in the first (group 2A) and second (group 2B) growth phases stimulated growth, as the final mean weights of groups 2A and 2B were 11% and 19% higher than those of the control group ( NNNNN). Growth in the control group and group 2C was arrested from January to May in the second year. Continuous light ( CCCCC) stimulated growth at the beginning of the trial, but the effect diminished at the end. Reduced male plasma 11-ketotestosterone (11- KT) and female estradiol 17β (E2) levels were found in groups 2A and 2B and continuous light group, as compared with the control group and group 2C at 26 months post hatch, indicating a higher age at first maturation in these groups. The 11- KT and E2 levels increased in May- June in group 2A indicating that first maturation was postponed by 6 months in this group, whereas first maturation was postponed by 1 year in group 2B and in the continuous light group. Photoperiod regime only had minor effects on flesh quality traits of the fish. [ABSTRACT FROM AUTHOR]

The effects of three different temperatures on the growth and maturation of the offspring of cultured versus wild populations of juvenile arctic charr ( Salvelinus alpinus L.) were investigated. The fish (start weight 17 g) were reared for 5 months at constant temperatures of 12, 14 and 16°C under a continuous light regime ( LD24:0). Growth performance was significantly influenced by both temperature and source population. The offspring from the farmed fish displayed significantly higher mean weights at all temperatures compared with the offspring from the wild fish. The results indicate that the optimal temperature for growth ( Topt) decreases with increasing fish size in the offspring of both cultivated and wild fish. Significant differences in length-weight relationship were found, with the offspring of wild fish displaying higher condition factor throughout the experiment. The results demonstrate that the offspring from multiple generation farmed population of arctic charr are better adapted to high temperatures compared with the offspring (F1 generation) from a wild population of arctic charr, and the former are also able to maintain growth at higher temperatures. There was a significant difference in maturation between the two populations, as the offspring from cultured fish displayed significantly lower level of maturation: 0%, 4% and 2% mature compared with 24%, 40% and 42% in the offspring from wild fish at temperatures of 12, 14 and 16°C respectively. The offspring from farmed strains of arctic charr thus appear to be the most suitable population for aquaculture. [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]

The effect of rearing temperature on the growth and maturation of Arctic charr ( Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October-April, size range 20-500 g) at constant temperatures of 9, 12 and 15 °C and according to two temperature-step groups ( T) i.e. fish transferred from 15 to 12 °C or from 12 to 9 °C. All the previous treatments were then reared either at 7 °C or at 12 °C for an additional 4 months (phase II, size range 300-1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 °C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 °C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 °C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase i.e. 4.18% (±0.79) and 7.29% (±0.89), for the temperature groups of 12 and 15 °C, respectively, compared with 2.49% (±0.74) for the 9 °C group. Our results suggest that for the production of fish >1000 g, moderate or low temperatures (here 9 °C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on-growing period. [ABSTRACT FROM AUTHOR]

The goal of this study was to determine the optimal stocking density for rearing juvenile spotted wolffish, Anarhichas minor (Olafsen), at two different sizes and assess the welfare status in relation to density. No major growth impairment was observed, although smaller fish (50–100 g) were significantly affected by density during the 120 days of the experiment, with final mean weights of 119.6 ± 11.6, 118.0 ± 5.8 and 88.7 ± 0.6 g for initial rearing densities of 10, 20 and 40 kg m−2 respectively. No effect of rearing density was seen for larger fish (100–160 g) during the 90 days of the experiment, with final mean weights of 160.2 ± 5.9, 159.7 ± 3.7 and 163.7 ± 11.5 g at fixed rearing densities of 20, 30 and 40 kg m−2 respectively. Our results suggest that the optimal rearing density of juvenile spotted wolffish is below 40 kg m−2 for smaller size fish (∼50–100 g) and probably ≥40 kg m−2 for the larger fish (100–160 g). Furthermore, it appears that the range of rearing density used did not have a significant effect on a selection of stress indicators (Na+ and K+ concentration, haematocrit, hepatosomatic index, total amount of plasma proteins and liver and muscle water content) and immunity response (plasma lysozyme activity) of juvenile spotted wolffish, making it a very tolerant species to crowding. [ABSTRACT FROM AUTHOR]

In order to study the possible interactive effects of salinity and photoperiod on growth, feed conversion, and blood chemistry in juvenile halibut, 2,604 (initial mean weight 26.8 g ± 0.2 SEM) juvenile halibut were exposed to six different combinations of salinities (13, 21, or 27‰) and photoperiods [continuous light, C and simulated natural photoperiod (65°N), SNP] for 129 days. Improved (10–20%) growth and 10–24% higher feed conversion efficiency were observed at low and intermediate salinities compared to the high salinity groups. Improved feed conversion efficiency (20%) and temporary growth enhancing effects (10%) of continuous light were observed, but effects faded out as day length in the simulated natural photoperiod group increased. No interactive effects of photoperiod and salinity on growth feed conversion or measured blood chemistry variables (blood sodium, pH level, haematocrit, bicarbonate content, and total carbon dioxide). It is suggested that juvenile Atlantic halibut should be reared at low and intermediate salinities and at continuous light, as this will improve growth and increase feed conversion efficiency. [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]

We compared growth properties of spotted wolffish with initial mean weight (± SE) 3.65 (± 0.15) kg reared in shallow raceways at three different densities (50, 70, and 90 kg/m2, corresponding to approx. 170, 240, and 310 kg/m3) in a 447-day-long growth trial at ambient temperature (mean (± SD), 4.2 C ± 1.9). Growth in all three groups was comparable, but there was a trend toward higher growth at the highest density. Final mean weights (kg ± SE) were 4.90 (± 0.15), 4.80 (± 0.16), and 5.05 (± 0.11), at the 50, 70, and 90 kg/m2 density, respectively. Initially, growth rates were higher at the 90 kg/m2 density group compared to the two other densities, but overall growth rates were similar in all three groups. Feed conversion efficiency differed and was higher at the two highest densities compared to lowest density. The acid–base balance was influenced by the density treatment as there was a general trend toward higher partial pressure of CO2 and HCO in the 90 kg/m2 group. Calculated productivity increased almost linearly with increasing stocking density and was found to be 24, 42, and 66 g/m2/day at 50, 70, and 90 kg/m2, respectively. The results show that the optimum density conditions for farming large spotted wolffish, both with respect to growth rate, feed conversion, and productivity are at densities equal to or higher than 90 kg/m2. [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 aim of this study was to investigate the effects of different salinities and temperatures and their possible interactive effect on growth performance, feeding parameters, and blood physiology in juvenile spotted wolffish, Anarhichas minor, reared at different temperature (7 and 10 C) and salinity (15, 25, and 34‰) combinations. There was a significant interactive effect between temperature and salinity on growth, as a growth-enhancing effect was seen at intermediate and full salinities at higher temperature, whereas the reciprocal trend was seen at lower temperature. Mean total feed consumption, daily feeding rate, and feed conversion efficiency were all highest at the intermediate salinity at 10 C, whereas at 7 C, the feeding parameters were highest at low and intermediate salinities. Blood plasma sodium content was lowest at 15‰, whereas the opposite trend was seen in partial pressure of CO2 and bicarbonate in blood where the highest concentrations were seen at 15‰. This study demonstrates that spotted wolffish has a high osmoregulatory and acclimatory capacity. In an aquaculture context, growth of juvenile spotted wolffish can be improved by rearing the species at high temperature and intermediate salinity combinations at least in a limited period of the juvenile phase. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the possible benefit of “temperature-steps” (T-steps) rearing for juvenile turbot (initial weight 15.1 g) under realistic production scale and to determine whether initial growth advantage is maintained throughout the rearing period to market size. One group (called T-step 22-19-16) of juvenile turbot was reared at three different temperatures, that is, 22 C (from 17 to 60 g) followed by 19 C (from 60 to 100 g) and 16 C (>100 g); another group (called T-step 19-16) at two temperatures, that is, 19 C (from 17 to 100 g) and lowered to 16 C (>100 g); and the third group (called C16) at one constant temperature, that is, 16 C. Relative growth was significantly higher in the two T-step groups, with the T-step 19-16 showing the highest overall growth. Feed conversion efficiency was highest in the 19-16 group. Only minor effects of the experimental rearing on blood physiology were found, with one notable exception of inverse relationship between plasma glucose and growth. Overall, these findings indicate that a short interval of rearing fish at high temperature during the early juvenile phase may have a long-term effect on biomass increment in turbot. This is an important finding for the turbot industry. [ABSTRACT FROM AUTHOR]

We compared growth properties of juvenile spotted wolffish with initial mean weight (±SE) 105.9 (±3.1) g reared in shallow raceways and conventional circular tanks in a 202-d-long growth trial at ambient temperature (approximately 4.0 C). From Day 41 onward, the fish in the shallow raceways was significantly larger, and final mean weights were 356.3 (±18.2) and 318.2 (±15.6), in the shallow raceways and the circular tanks, respectively. Overall, growth rates were 14% higher (0.62%/d) in the shallow raceway group compared to the circular tanks (0.52%/d). Feed conversion efficiency differed and was 17% higher in the shallow raceways (1.01) compared to the circular tanks (0.84). Correlation between adjacent growth rates was more profound in the circular tanks (mean Spearmans rank, rSp = 0.38) than in the shallow raceways (mean rSp = 0.15). This could indicate a stronger social hierarchy in conventional tanks leading to suppressed growth, which is in line with the growth data presented in this study. The findings of the present study may have important consequences for optimization of commercial production of spotted wolffish and could be applicable to other bottom-dwelling species. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Growth, feed conversion efficiency and frequencies of skeletal deformities were studied in juvenile Atlantic cod ( Gadus morhua) that had been startfed on either rotifers (rotifer group) or zooplankton (zooplankton group). After metamorphosis, the fish were reared at four constant temperatures (7, 10, 13, 16°C) or moved successively from 16 to 13 and 10°C (T-step, average 13.2°C). The zooplankton group had a consistently higher growth rate at all the temperatures studied. Further, the zooplankton group had higher food intake (20%) and higher feed conversion ratio (1.65 vs. 1.31). In addition, a significantly higher incidence of skeletal deformities was found in the rotifer group (14.2%) compared with the zooplankton group (4.1%). After termination of the laboratory study, the fish were reared in sea pens under ambient conditions for 17 months. Final weights of the zooplankton group were consistently larger (between 12% and 14% larger depending on original temperature groups). To verify the growth results, we conducted a follow-up study where a single egg group was divided into two parts and fed either on rotifers or zooplankton. This study indicated similar growth differences as found in the first study. Overall, our data suggest that different startfeeding diets may be important for long-term growth, incidence of deformities and quality of juvenile cod. The use of zooplankton can greatly improve long-term growth and quality of cod juveniles. The study also highlights the advantage of using elevated temperatures in the juvenile phase as this will lead to significantly higher final weights in the adult stage. [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.

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]

The effect of thermal history (11°C and 14°C) on growth of juvenile halibut, Hippoglossus hippoglossus (L.) (initial mean weight 140 g, n = 254), was studied. Fish were divided into four groups, two groups remaining at constant temperature (C11, C14), and fish in the other groups being transferred from either 11°C to 14°C (F11:14) or from 14°C to 11°C (F14:11). Twenty fish in each tank were tagged (PIT) at the start of the experiment. The final mean weights were significantly higher in F14:11 (384 g) than in F11:14 (308 g) and C14 (317 g). Further, F14:11 had significantly higher length growth rate (SLGR) than both F11:14 and C14. No significant differences between the experimental groups within each temperature (F14:11 vs. C11, and F11:14 vs. C14) were, however, found. Growth rate (SGR) declined rapidly with increasing size (from 1.4–1.8% day-1 to 0.4–0.8% day-1). It is concluded that the optimal temperature for growth of juvenile halibut declines with increasing size. Thus, as halibut grow larger, the temperature should be reduced to take advantage of this change in optimal temperature for growth. [ABSTRACT FROM AUTHOR]

Abstract There is still much disagreement and debate about whether or not genetically based growth differences occur in Atlantic cod, and there is evidence on both sides. In this review, data on genetically based growth differences in cod will be presented to shed light on this hypothesis. Motivated by the hypothesis that growth patterns may reflect specific genotype adaptations, we review stock-specific responses on growth. An example of genetically based differences between the population units at two spawning localities off south Iceland is discussed. Here, significant differences in growth performance of the different Syp -I genotypes were found. Also, the cod sampled at Loftstaðahraun displayed higher mean weight and length compared to the cod from Kantur indicating that these population units may display different life histories. Other studies have shown conflicting results depending on which side of the Atlantic the problem has been investigated. We propose that a common-garden meta-analysis with several cod stocks from both sides of the Atlantic is needed to give any reasonable answer to the question of genetically based growth differences. Until such studies have been conducted, it is premature to conclude one way or the other. In this review, we have not tried to quantify how large the environmental part of growth regulation versus the genetic part is, as this information is not available in the published literature on cod. Based on recent research on two flatfish species (turbot and Atlantic halibut), approximately 30% of growth variation is caused by genetical factors, but it remains to be seen if this is similar in cod. A fruitful way to continue this research might be to conduct controlled experiments, where performance (growth, food intake, feed conversion efficiency, feeding behaviour, etc.) and environmental factors (e.g. temperature, oxygen, photoperiod, predation risk, food availability) are studied simultaneously for different genotypes... [ABSTRACT FROM AUTHOR]