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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]

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]

In order to test seasonal, rearing, maturing and anaerobic muscle activity effect on the flesh quality of turbot ( Scophthalmus maximus) a total of 80 farmed turbot from three different strains from reared under natural or continuous light were killed by a percussive blow to the head in November (winter, Icelandic strain), March (spring, Portuguese strain) and June (summer, domesticated strain (France turbot)). To test the effect of anaerobic muscle activity, 10 fish were on each occasion pre rigor filleted, where one fillet was used as a control, while the other fillet was electrically stimulated using a squared 5 Hz, 10 V pulsed DC for 3 min. All pre rigor fillets were measured for pH, weighed, wrapped in aluminum foil and stored in polystyrene boxes with ice. After 7 days of storage the fillets were measured instrumentally for pH, drip loss, colour (CIE L* a* b*) and texture properties such as hardness and shear force, while fillet shrinkage and colour (RBG) were evaluated with computer imaging on photographs from a standard lightbox. Results showed that softness of the flesh was mainly influenced by factors associated with growth, such as season, photoperiod and maturation. Anaerobic muscle activity simulated with electrical stimulation caused an increase in drip loss (<1%) and loss of shear force (<4%), but had no effect on hardness or fillet shrinkage. Computer imaging revealed that muscle contractions related to the electrical stimulus forced out blood from the fillet causing less reddishness for the entire storage period. We conclude that a pH drop upon slaughter associated with anaerobic muscle activity has a minor effect on the flesh quality in the short run, while seasonal/alternatively genetic effects are predominant. [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 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]

Interactions between temperature and photoperiod on growth of Atlantic cod (Gadus morhua) juveniles (initial weight 9.1 g) were studied by rearing juvenile cod 3 months under simulated natural photoperiod (LDN) and continuous light (LD24:0) at 7, 10, and 13 °C. Juvenile Atlantic cod exposed to LD24:0 had higher growth rate and better feed conversion efficiency compared with cod reared under LDN. Optimal temperature for growth of juvenile Atlantic cod in the size range 5–50 g was influenced by photoperiod and was estimated to be 12.3 °C under LD24:0 and 15.7 °C under LDN. After termination of the laboratory study, the fish were reared in sea pens at ambient conditions for 17 months. The growth-enhancing effect of LD24:0 could be traced far beyond the duration of the laboratory trial, as the final mean weights in June 2005 of the fish reared at LD24:0 and 13 and 10 °C in the laboratory trial were 8% and 13% higher than those of the respective LDN groups. Our study indicates a physiological mechanism that might be linked to cod migrations, as maximal growth and feeding efficiency will be attained in areas during a season with extended day length or continuous light. [ABSTRACT FROM AUTHOR]

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]

Abstract: A group of juvenile turbot (mean (SE), initial weight 22g (1.5)) were reared in indoor and covered outdoor tanks under ambient temperature conditions for 46months until harvest (mean final weight, 2.7kg). The photoperiod treatment was divided into 5 phases where the fish in each phase were exposed to either 16h of light and 8h of darkness (LD16:8, extended light, E) or continuous light (C). Thus, the following five photoperiod combinations were tested: a) LD16:8 (Control) group (EEEEE), b) Group 2A (ECEEE), c) Group 2B (EECEE), d) Group 2C (EEECE), and e) Continuous light (CCCCC). Long term rearing on continuous light reduced growth, whereas short term exposure to continuous light stimulated growth as the final mean weights of Groups 2C and 2B were 16 and 11% higher than those of the Control and the Continuous light groups. Significantly higher male plasma 11-ketotestosterone levels were seen in the Control group in July 2011 (5.67ngmL−1) and June 2012 (2.56ngmL−1) than in the other experimental groups, indicating delayed maturity in groups reared under continuous light. Estradiol 17-β levels were low in all groups throughout the experiment indicating low or no female maturation. Photoperiod regime had only minor effect on flesh quality traits of the fish. Based on current results, we recommend that turbot is farmed at extended light (i.e. LD16:8) in combination with continuous light during spring and summer (i.e. Group 2C in this study) during the second production year. [Copyright &y& Elsevier]