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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 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]

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]

Abstract: The protein requirements of Atlantic halibut (Hippoglossus hippoglossus L) were tested in two trials for fish with initial size of 564 g and 973 g. The fish were fed near isocaloric diets with crude protein in dry matter (CP) between 35% and 53%. There was no significant effect of CP on weight development or SGR, daily feed intake or protein efficiency ratio in either trial. However, CP significantly affected the feed conversion (FCR) of the smaller fish with FCR increasing at lower CP. The CP did not affect the final protein or lipid content of the fish. The results of the study suggest that the minimum CP for maximum growth is 41% and 35% for 560 g and 970 g halibut respectively. [Copyright &y& Elsevier]

Abstract: A group of juvenile Atlantic halibut (mean, SD, 199.5 g, 44.7) was split into two experimental groups: one group was fed in excess twice a day and later five days a week (i.e. Control group), and the other group was starved for 5 weeks and then subsequently re-fed for 10 weeks (i.e. 5/10 starvation/re-fed group). This treatment was repeated for three years until the fish were harvested (mean final weight, 4.4 kg). A size +specific compensatory response was seen; partial compensation was observed in halibut weighing less than 500 g whereas full recovery growth was seen in halibut over 2 kg. Food consumption and feed conversion efficiency was measured during two full 5/10 starvation/re-fed cycles. The Control group consumed 86% more food in the measurement period, whereas the FCE 40% higher in the 5/10 starvation/re-fed group (FCE=0.95) compared to the Control group (FCE=0.68). In males lower gonadosomatic index (2.2 vs. 3.0) and plasma 11-ketotestosterone (0.22 vs. 1.26 ng ml−1) levels in the 5/10 starvation/re-fed group were observed during late winter and spring of 2006 (age 3 years) indicating higher age at 1st maturity. Starvation had a significant effect for improving the quality as starved fish had higher muscle pH (6.4 vs. 6.2), less gaping (0.1 vs. 0.3) and harder texture (61.4 vs. 57.6 N). Overall, the rearing on a repeated 5/10 starvation/re-fed regime for 3 years led to full growth compensation, higher feed conversion efficiency, lower male maturation and improved flesh quality. [Copyright &y& Elsevier]

Abstract: The effects of photoperiod and feeding regimes on plasma IGF-I levels and their relationship with growth rate of juvenile halibut (initial mean weight 364 g) were investigated by rearing fish under five different photoperiod regimes and two feeding regimes for 14 months. The entire photoperiod experiment was divided into 3 phases where the fish in each phase were exposed to either natural photoperiod (N), stimulated photoperiod with long day and short night (S) or continuous light (L). Thus, the following five photoperiod combinations were tested: a) Control group (NNN) b) Group 2A (NLN) c) Group 2B (NNL) d) Long day-natural group (SNN) e) Production group (LNN). In addition, the Control group was split into two parts and fed according to two different feeding regimes: a) Continuous fed group: Fish fed every day. b) Starvation/re-fed group: Fish were starved for 5 weeks and then re-fed for 10 weeks, and the treatment repeated during the whole experimental period. The analyses of IGF-I were performed from individually tagged fish in all groups in September 2005 and March 2006. In order to test how rapidly starvation affects circulating IGF-I levels samples were taken from the Starvation/re-fed group after a 10 days starvation (September) and immediately after 10 weeks of feeding (March). A significant relationship between IGF-I levels and individual growth in the preceding period and photoperiod and starvation treatment was found on both occasions. In conclusion, the present study indicates that plasma IGF-I levels are correlated to growth in Atlantic halibut, and affected by photoperiod treatment or compensatory growth during re-feeding. Correlation between individual growth rate and IGF-I levels was low, but significant, highlighting the complexity of how environmental factors affect the endocrine and physiological regulation of growth in fish. [Copyright &y& Elsevier]

Abstract: The effect of salinity on growth, feed conversion efficiency and blood physiology was investigated by rearing Atlantic halibut Hippoglossus hippoglossus (initial weight 25.5±0.8 g, mean±SEM) at salinities of 15, 25 or 32‰ for 4 months at 12 °C. The final mean weight of the fish reared at 15‰ (135.9±5.1) and 25‰ (130.8±5.1) was significantly larger than that of fish reared at 32‰ (107.6±5.2). Similarly, the specific growth rates (SGR) and feed conversion efficiency (FCE) were significantly higher at both 15‰ (SGR: 1.29±0.03; FCE: 1.21±0.04) and 25‰ (SGR: 1.25±0.04; FCE: 1.18±0.06) compared to 32‰ (SGR: 1.16±0.04; FCE: 0.97±0.10). Of the osmoregulatory and metabolic parameters analysed in plasma Na+ and glucose were significantly lower in fish reared at 15‰ compared to both 25‰ and 32‰. The acid–base balance was influenced by the salinity treatment as there was a general trend towards higher pH, pCO2 and HCO3 − in the full salinity group compared to the 15‰ group. The results clearly show that the optimum conditions for farming Atlantic halibut, both with respect to growth rate and feed conversion, is at salinities lower than 32‰. This is an important finding for the halibut industry. [Copyright &y& Elsevier]

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]

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]

Growth of juvenile Atlantic halibut from three areas of the North Atlantic (Canada, Iceland and Norway) was studied in an experiment using individual tagged fish reared at 15°C for 85 days. Fish from each population were subsequently split into two groups and acclimatised to either 12°C or 18°C. The fish were then injected intra-peritoneally with a Vibrio anguillarum bacteria suspension and mortality monitored for 4 weeks. Growth rates of the Canadian population ranked lowest, whereas the Norwegian population had the highest mean growth rates (SGR=1.70% day−1, 1.62% day−1 and 1.53% day−1 for the Norwegian, Icelandic and Canadian populations, respectively). The halibut from Norway had the best survival following bacterial challenge (80%, 50% and 55% survival for the Norwegian, Icelandic and Canadian populations, respectively). Mortality was higher at 18°C than at 12°C in the Icelandic (62% at 12°C and 27% at 18°C) and Canadian (56% at 12°C and 32% at 18°C) fish, whereas a smaller difference between temperatures was observed in the Norwegian fish (25% at 12°C and 13% at 18°C). Fish that survived the challenge test were those that had grown fastest in the growth trial. Low, but significant, correlations between survival and size and growth were seen, but these correlations varied between populations. In the Canadian population, no correlation between size and growth and survival were seen; only size was correlated (r=0.27) with survival in the Icelandic population, whereas both size (r=0.18) and growth (r=0.17) were correlated with survival in the Norwegian population. [Copyright &y& Elsevier]

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: The effects of chronic and periodic exposure to un-ionised ammonia (UIA) on growth and food conversion efficiency in juvenile Atlantic halibut, Hippoglossus hippoglossus were examined. Fish with a mean (SD) initial weight 51.7 (13.2) g, were exposed to five treatments consisting of a control group, three chronic groups (Chronic Low, Chronic Medium and Chronic High, ambient UIA levels of 0.06, 0.12 and 0.17mgl−1, respectively), and one group exposed to a daily peak of ambient UIA, closely corresponding to the chronic high level (max level 0.17mgl−1 UIA, High Pulse). The fish were reared at 12.0°C, pH 8.0, 34gl−1 salinity and about 80% oxygen saturation. The fish were reared under these conditions for 62days, followed by a 38 day period where no ammonia was added. Chronic medium- and high levels of ambient ammonia had a deleterious effect on growth performance via appetite suppression, whereas the periodic ammonia treatment conducted in the present experiment had little or no effect on growth performance. No growth reduction was seen in the Chronic Low group, thus a NOEC value (No Observed Effect Concentration) of 0.06mgl−1 ambient UIA is proposed for juvenile Atlantic halibut. No indication of ion regulatory or acid base regulatory stress in the fish exposed to chronic or periodical peaks of ambient UIA was found despite minor differences in measured blood parameters. [Copyright &y& Elsevier]

Abstract: Juvenile Atlantic halibut (40.5±9.1g mean initial body mass±SD) were reared at five different levels of oxygen availability (57%, 84%, 100%, 120%, and 150% of air saturation) for 94days. The availability of oxygen significantly affected the growth rate of the fish while feed conversion was not significantly different. The final size of fish reared at 57% of air saturation was significantly lower than in groups reared at 100% to 150% of air saturation and the specific growth rate (SGR) in the 57% group over the 94day period was significantly lower than in all other groups. The increase in biomass was 45% higher in the group exposed to 100% of oxygen saturation than in the group reared at 57% saturation. The group reared at 84% of air saturation was intermediate and the final size of this group was significantly different from fish reared at either 57% or 100%–150% of air saturation. There was no significant difference in the growth trajectories of fish reared at 100%–150% of air saturation but they were significantly different from those of fish reared at either 57% or 84% saturation. This suggests that the growth of halibut is progressively increased when the oxygen saturation is increased from 57% to 100% while further increase in oxygen saturation does not improve the growth rate. When oxygen saturation was increased, the blood pH increased as did the partial pressure of CO2, total concentration of CO2 and bicarbonate in blood. This change is likely a result of reduced ventilation rate with increased oxygen saturation. The results challenge the common recommendation that 60%–80% oxygen saturation is adequate to support maximum growth of fish. The results of the present study suggest that there may be an advantage for halibut farmers to increase the oxygen availability from the recommended 60%–80% oxygen saturation up to 100%. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate the effects of short term starvation periods on growth response and fillet crude composition of juvenile halibut. Fish were fed to satiation twice a day or starved in four feeding schedules as follows; feeding (F) 99 days (Control); 11 days starvation (S), followed by 20 days F, 14 days S, 22 days F, 11 days S and 21 days F (Starvation A); 16 days S, 28 days F, 16 days S and 39 days F (Starvation B); 32 days S and 67 days F (Starvation C). Each tank contained 70 fish with an initial mean weight (SD) of 195.7 (46.6) g. All starvation groups showed partial compensation during re-feeding, displaying an increase in daily feeding rate and a tendency towards increased feed conversion efficiency compared to the control group. The length of the re-feeding periods was, however, insufficient to let the starved halibut catch up with the fish weight in the control group although growth rate in the last sampling period up to day 99 was significantly higher in the starvation groups than in the control group. The results indicated that the experiment was ended in a phase when the fish were still undergoing compensatory growth. The results further indicate that as much as 32 days of starvation and subsequent feeding does not affect the fillet composition of juvenile halibut. [Copyright &y& Elsevier]