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Effects of a simulated short winter period on growth in wild caught Arctic charr (Salvelinus alpinus L.) held in culture
Aquaculture 287 (2009) 431–434
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Aquaculture j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / a q u a - o n l i n e
Short communication
Effects of a simulated short winter period on growth in wild caught Arctic charr (Salvelinus alpinus L.) held in culture Sten Ivar Siikavuopio a,⁎, Bjørn-Steinar Sæther a, Steinar Skybakmoen b, Christian Uhlig c, Espen Haugland c a b c
Nofima, N-9291 Tromsø, Norway Fishfarming Technology, N-9500 Trondheim, Norway Bioforsk, Norwegian Institute for Agricultural and Environmental Research (Bioforsk), Arctic Agriculture and Land Use Division, N-9269 Tromsø, Norway
a r t i c l e
i n f o
Article history: Received 28 January 2008 Received in revised form 30 October 2008 Accepted 31 October 2008 Keywords: Photoperiod Growth Arctic charr Salvelinus alpinus
a b s t r a c t This study investigates how simulation of condensed winter light conditions effects the growth of wild caught Arctic charr (Salvelinus alpinus L.) held in culture. After capturing from Altevatn, Northern Norway, juvenile Arctic charr were cultivated and subsequently individually divided into two groups. The fish were held under identical conditions from May to October including continuous light. Starting from week 41 after capture (October) one group was subjected to a winter light regime of 6 h light and 18 h dark per day (Winter Light group—WL), while light regimes in the second group remained continuous (Light group). After an eight weeks treatment period the WL-group was reverted to the continuous light regime until the experiment ended in May 2007. Results revealed no pre-treatment differences in growth between the two groups. However, starting from two months after the short day treatment, fishes from the WL group had significant higher growth rates compared to L group fish. At the end of the experiment, e.g. five months after the light treatment, fishes from WL group had increased their average body weight by 353 g as compared to 252 g in the L group. Consequently, results show that simulation of winter light conditions can increase the productivity of landbased Arctic charr (Salvelinus alpinus L.) cultivation by 25 to 30%. Thus, management of wild caught charr farming, great care should be taken as to what light regimes the fish are exposed to. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Arctic charr (Salvelinus alpinus L.) is the northernmost distributed freshwater fish and is considered the most cold-adapted species within the salmonid family (Johnson, 1980). Growth of Arctic charr populations are known to be highly variable under natural conditions (Johnson, 1980; Hammer, 1984). Due to its distribution, Arctic charr experience considerable seasonal changes in photoperiod throughout the year. The charr seems very well adapted to these changes, enabling the species to utilise the rapid seasonal changes in resource availability in the northern areas (Johnson, 1980). Changes in photoperiod is one of the more rigid environmental cues to the fish with its effects widely studied, and it is particularly known to influence on feeding, growth and maturation of Arctic charr (Mortensen and Damsgård, 1993; Frantzen et al., 2004). In general, food intake and growth of Arctic charr is highest during spring and early summer when day length increase continuously from 0 (polar night) to 24 h (midnight sun) (Tveiten et al., 1996; Kestemont and Baras, 2001; Johnston, 2002). It is the change from short to long day in spring that trigger this shift in
⁎ Corresponding author. Tel.: +47 776 29000; fax: +47 776-29100. E-mail address: Sten.siikavuopio@fiskeriforskning.no (S.I. Siikavuopio). 0044-8486/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2008.10.060
growth potential, rather than the long day per se. As demonstrated by Mortensen and Damsgård (1993), juvenile Arctic charr cultivated under constant short- or long-day conditions grew at comparable rates, while growth rates of fishes that experienced short-day conditions followed by long-day conditions were significant higher. Furthermore, Sæther et al. (1996) suggests that Arctic charr has an endogenous growth and maturation rhythm independent of external photoperiod information, which indicates that their life cycle is genetically adapted to artic light conditions. Basic biorhythm research describes that environmental cues, like photoperiod, serve to synchronise annual endogenous rhythms, and as such, the changes in photoperiod are likely to adjust the endogenous rhythms controlling seasonal events (Gwinner, 1981). The importance of photoperiod on growth and life cycle is not restricted to Arctic charr but applies also to other salmonids. Consequently, photoperiod manipulation is a key tool within salmonid production (Taranger et al., 1999; Bromage et al., 2001; Peterson and Harmon, 2005; Nordgarden et al., 2005). Systematic studies on the effect of abrupt changes in photoperiod on growth in Arctic charr are scarce and little is known about the possibilities of improving productivity through photoperiod manipulation in Arctic charr farms. This study aimed to investigate the effects of a temporarily winter light-regime on growth and production
432
S.I. Siikavuopio et al. / Aquaculture 287 (2009) 431–434
Table 1 Development of SGR, condition factor (K) and survival (S) of Arctic charr (Salvelinus alpinus L.) cultivated at continuous light (L) or simulated winter photoperiod (WL) Time
L (SGR)
WL (SGR)
Time
L (K)
WL (K)
May–June June–Sep. Sep.–Oct. Oct.–Nov. Nov.–Dec. Dec.–Jan. Jan.–Mar. Mar.–May
1.72 (0.02)a 0.90 (0.12)a 0.35 (0.05)a 0.32 (0.07)b 0.10 (0.01)a 0.31 (0.09)a 0.59 (0.08)a 0.42 (0.03)a
1.60 (0.03)a 0.93 (0.07)a 0.45 (0.13)a 0.09 (0.01)a 0.13 (0.03)a 0.46 (0.05)a 0.86 (0.05)b 0.62 (0.02)b
May 2006 Dec.2006 May 2007
1.16 (0.26)a 1.22 (0.18)a 1.28 (0.18)a
1.17 (0.18)a 1.22 (0.18)a 1.39 (0.14)b
L (S)
LW (S)
78%
79%
Different letters denote significant differences (P b 0.05). Data are presented as mean ± S.D.
of a juvenile Arctic charr (Salvelinus alpinus L.) population in a northern Norwegian fish farm.
factor (K) is calculated according to the length–weight relationship as follows; K = 100WLT− 3 where W is the weight of the fish and LT the corresponding total length.
2. Material and methods 2.3. Statistical analysis 2.1. Fish and rearing The wild caught Arctic charr (Salvelinus alpinus L.) used in this experiment originated from lake Altevatn in Bardu (68°N, 19°E). The individual fish weight at the day of capture (5 April 2006) varied between 10 and 25 g. The fish were held in a 4000 l tank at Villmarksfisk in Bardu during the first month. They were weaned to dry feed during a two week period by adding 10% cod roe to the dry feed at day one, and gradually reduce this to 0 addition on day 14. Following weaning the fish were fed formulated dry feed, using a recipe adapted to Arctic charr, (Skretting®, Stokmarknes, Norway). Feed rations were surplus by 20% according to the feed table developed for Arctic charr by Jobling et al., 1993. Following weaning the fish were held at continuous light (24L), with light intensity measured to 150 lx at the water surface (fluorescent lamp) and constant water temperature of 8 °C (±0.5 °C) until the onset of the experiment in May 2006. Two weeks prior to the start of the experiment 200 of totally 1200 fish were anaesthetized using 80 µl l− 1 benzocaine and individually tagged with fingerling tags (Floy-Tag) attached through the musculature just anterior to the dorsal fin. The fish were randomly distributed into four 2000 litre fibreglass tanks, with 50 tagged and 250 untagged fish per tank. The tanks were assigned to two treatment groups in May but kept under identical conditions until October, when photoperiod treatment began. Starting from week 41 after capture (October) fishes in tanks 1 and 3 were given a winter light regime of 6 h light and 18 h dark per day (Winter Light group), while light regimes in tanks 3 and 4 remained unchanged (Light group). After eight weeks with winter light regime group WL were reverted to the 24 h light regime until the end of the experiment in May 2007. Water temperature was kept at 8.0 °C (±0.5 °C ), continuously recorded in the inflow water using EBI-125A, WINLOG 2000-S temperature loggers. Water oxygen and pH levels were measured weekly with Handy Delta logger and Oxygard pH logger, (OxyGuard®), in the tank effluent water; readings throughout the entire experimental period indicated oxygen levels above 80% and pH levels of 7.5 (0.01) at all times. Levels of total ammonia–nitrogen (TAN = 0.66 (0.13) mg/l), nitrite (NO2 = 0.41 (0.11) mg/l), and nitrate (NO3 = 21.5 (4.8) mg/l) were determined two times weekly using Nova 30 spectrophotometer (Spectroquant®).
Data are presented as mean ± standard deviation (S.D.). For statistical analysis STATISTICA™ (StatSoft, 2002) was used. The normal distribution of data were tested using Kolmogorov–Smirnov adapted by Lilliefors and possible statistical differences analysed with a twoway ANOVA. Statistical differences in SGR and K were analysed with a one-way ANOVA. Significance was assumed when P b 0.05. 3. Results During the first 10 months of the growth trial, there were no consistent significant differences in either weight increase or specific growth rate between the two groups. During winter light treatment, the weight increments in the WL group tended to lag behind the continuous light group, and the SGR of WL fish was significantly lower than L fish during the October–November period (Table 1). This tendency changed already one month after the treatment ended (January) and following this point in time, the group that had undergone the winter light period had significantly higher body weight (Fig. 1; F8,18 = 36.627, P = 0.001) and specific growth rate (Table 1; F1,2 = 37.098, P = 0.025) as compared to the group held on continuous light. The SGR were highest during summer
2.2. Measured parameters At the start and the end of the experiment individual length (precision 0.1 cm) and weight (0.5 g) of all Arctic charr was measured. All growth estimates are based on length and weight measurements of the individually tagged fish (total n = 200), which were sampled at day 0, 40, 120, 150, 180, 210, 260, 310 and 360. Specific growth rate (SGR) was calculated according to the formula: SGR = (eg − 1) ⁎ 100, where g = (lnW2 − lnW1)(t2 − t1)− 1 and W2 and W1 are weights (g) at days t2 and t1, respectively. The condition
Fig. 1. Weight increase (gram) of Arctic charr (Salvelinus alpinus L.) reared under cultivated at continuous light (L) or simulated winter photoperiod (WL). The arrow marks the start and the end of the two months short day treatment of group LW. Different letters denote significant differences (P b 0.05).
S.I. Siikavuopio et al. / Aquaculture 287 (2009) 431–434
right after capturing; declining towards autumn with minimum for WL in October–November, and for L during November–December. The SGR increased during December, January and February, but reduced again by approximately 20% in the period between March and May. The SGR ended markedly lower compared to the period after capture in May– June 2006. The condition factor were significant higher in the WL group at the end of the experiment (F1,2 = 62.581, P = 0.0158) as compared to fish that only experienced continuous light after capture (Table 1).The mortality rates during the 12-month experiment were about 20% and did not differ between groups (Table 1). 4 Discussion 4.1. Growth The growth was identical in both groups between tagging and onset of treatment, providing a good starting point for the experiment. The winter light treatment apparently led to reduced growth performance. However, following the condensed winter, this fish entered what resembles a growth compensation that can be associated with a shift in seasonal changes in growth potential (Sæther et al., 1996; Tveiten et al., 1996). At the end of the experiment, and five months after the different light treatments, fishes from group WL had increased their average total weight by 353 g compared to 252 g of group L. These results show that simulation of natural winter light conditions can increase the subsequent growth rate of Arctic charr, at least temporarily. The growth rate data in this study resembles results obtained on juvenile Arctic charr by Mortensen and Damsgård (1993). The development of the specific growth rate (SGR) showed a clear temporal pattern for both trails. Winter depression with a reduction in SGR from about 1.6% in summer to about 0.1% in late autumn followed by a significant increase in SGR from January to February but stagnation from March to May. Temporal cycling in food intake, growth and body fat stores have been described in several species of animals held under controlled conditions, with species living at high latitudes that appear to exhibit the greatest seasonal fluctuations (Jobling, 1994, Loudon, 1994, Tveiten et al., 1996, Jobling et al., 1998, Oppedal et al., 2006). Sæther et al. (1996) demonstrated that even though environmental factors such as photoperiod and temperature were constant there persist some seasonal changes (indicating endogenous control) of growth in Arctic charr. The changes in specific growth rate pattern in the reported study are similar to results obtained by Sæther et al. (1996). The temporal difference in growth response in these two groups can be due to the “winter” information given only to the WL group, adjusting their internal rhythm to proceed to spring conditions when day length again increased (Gwinner, 1981). Endocrine control is involved in growth and there is information on the direct effect of light on the release of several hormones, mainly growth and thyroid hormones (Jobling, 1994, Boeuf and Le Bail, 1999, Evans and Claiborne, 2006). However, the seasonal timing effect of photoperiod may act stronger on the growth performance, as is also seen in this trial. For production management it is important to realise that effects of light on consecutive growth depend on the physiological state of the animal when received, and manipulation of photoperiod should be used with great care to gain the planned result (Gwinner, 1981). Endogenous rhythms are only receptive to environmental stimuli that is in accordance with the time phase they are in, e.g. manipulation should aim at condensing, stretching or phase shift seasons, not jump them. 4.2. Mortality The accumulated mortality was about 20% for both light treatments at the end of the experiment. However, mortality was highest during the first 90 days of cultivation. The absence of food in the stomach of the majority of the dead fish, suggest that they had been
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unable to adapt to indoor cultivation conditions, including weaning to dry feed. However, overall mortality between the two different light treatments did not differ, indicating comparable physical, chemical and biological conditions between the groups. 4.3. Conclusion and perspectives This results clearly indicate that better growth were obtained in Arctic charr that received a winter light stimuli, for 8 weeks (6L: 18D) compared to Arctic charr reared under continuous light. This winter stimuli came after a period with continuous light, when the fish is expecting and receptive to a winter signal. Consequently, results show that simulation of condensed winter light conditions can increase the productivity in land-based Arctic charr cultivation by at least 25 to 30%. Use of changes in photoperiod should therefore gain more attention in production management processes. It is important to realise the limitations involved, and that the changes are likely to be temporal. Further studies on seasonality and growth in Arctic charr culture is are needed to fully understand the importance of endogenous rhythms controlling feeding, growth and maturation and how to utilise them to their potential. Acknowledgements The Norwegian Research Council, project no. 167941/110, supported this study. We would also like to thank Dagfinn Lysne and Nils Steien at VillmarksFisk for their technical assistance and advice on this work. References Boeuf, G., Le Bail, P.-Y., 1999. Does light have an influence on fish growth? Aquaculture 177, 129–152. Bromage, N., Porter, M., Randall, C., 2001. The environmental regulation of maturation in farmed finfish with special reference to the role of photoperiod and melatonin. Aquaculture 197 (1–4), 63–98. Evans, D.H., Claiborne, J.B., 2006. The Physiology of Fishes. Third edition, CRC Press, Taylor & Francis Group. 602 pp. Frantzen, M., Arnesen, A.M., Damsgård, B., Tveiten, H., Johnsen, H.K., 2004. Effects of photoperiod on sex steroids and gonad maturation in Arctic charr. Aquaculture 240 (1–4), 561–574. Gwinner, E., 1981. Circannual systems. In: Aschoff, J. (Ed.), Handbook of Behavioural Neurobiology volume 4 Biological Rhythms. Plenum press, New York, pp. 391–410. Hammer, J., 1984. Ecological characters of different combinations of sympatric populations of Arctic charr in Sweden. In: Johnson, L., Burns, B.L. (Eds.), Biology of the Arctic Charr. Proceedings of the International Symposium of Arctic Charr, Winnipeg, Manitoba, May 1981. University of Manitoba Press, Winnipeg. 35–63 pp. Jobling, M., 1994. Fish Bioenergetics. Chapman and Hall, London. 309 pp. Jobling, M., Jørgensen, E.H., Arnesen, A.M., Ringø, E., 1993. Feeding, growth and environmental requirements of Arctic charr: review of aquaculture potential. Aquaculture international 1, 20–46. Jobling, M., Tveiten, H., Hatlen, B., 1998. Cultivation of Arctic charr: an update. Aquaculture international 6, 181–196. Johnson, L., 1980. The Arctic charr, Salvelinus alpinus. In: Balon, E.K. (Ed.), Charrs, Salmonid Fishes of the Genus Salvelinus. W. Junk, The Hague, Netherlands. 87 pp. Johnston, G., 2002. Arctic Charr Aquaculture. Blackwell Publishing. 272 pp. Kestemont, P., Baras, E., 2001. Environmental factors and feed intake: mechanisms and interactions. In: Houlihan, D., Boujard, T., Jobling, M. (Eds.), Food Intake in Fish. Blackwell Science Ltd. 131–156 pp. Loudon, A.S.I., 1994. Photoperiod and the regulation of annual and circannual cycles of food intake. Proceeding of the Nutrition Society 53, 495–507. Mortensen, A., Damsgård, B., 1993. Compensatory growth and weight segregation following light and temperature manipulation of juvenile Atlantic salmon (Salmon salar L.) and Arctic charr (Salvelinus alpinus L.). Aquaculture 114, 261–272. Nordgarden, U., Hansen, T., Hemre, G.I., Sundby, A., Björnsson, B.T., 2005. Endocrine growth regulation of adult Atlantic salmon in seawater: the effects of light regime on plasma growth hormone, insulin-like growth factor-I and insulin levels. Aquaculture 250, 862–871. Oppedal, F., Berg, A., Olsen, R.E., Taranger, G.L., Hansen, T., 2006. Photoperiod in seawater influence seasonal growth and chemical composition in autumn seatransferred Atlantic salmon (Salomo salar L.) given two vaccines. Aquaculture 254, 396–410. Peterson, R.H., Harmon, P.R., 2005. Changes in condition factor and gonadosomatic index in maturing and non-maturing Atlantic salmon (Salmo salar L.) in Bay of Fundy sea cages, and the effectiveness of photoperiod manipulation in reducing early maturation. Aquaculture Research 36 (9), 882–889.
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Sæther, B.-S., Johnsen, H.K., Jobling, M., 1996. Seasonal changes in food consumption and growth of Arctic charr exposed to either simulated natural or a 12:12 LD photoperiod at constant water temperatures. Journal of Fish Biology 48 (6), 1113–1122. StatSoft, 2002. CSS. STATISTICA User's Guide, Version 6.1. StatSoft Inc., Tulsa, OK. 1095 pp.
Taranger, G.L., Haux, C., Hansen, T., Stefansson, S.O., Björnsson, B.T., Walther, B.T., Kryvi, H., 1999. Mechanisms underlying photoperiodic effects on age at sexual maturity in Atlantic salmon, Salmon salar. Aquaculture 177 (1–4), 47–60. Tveiten, H., Johnsen, H.K., Jobling, M., 1996. Influence of maturity status on the annual cycles of feeding and growth in Atlantic charr reared at constant temperature. Journal of Fish Biology 48, 910–924.
Contents lists available at ScienceDirect
Aquaculture j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / a q u a - o n l i n e
Short communication
Effects of a simulated short winter period on growth in wild caught Arctic charr (Salvelinus alpinus L.) held in culture Sten Ivar Siikavuopio a,⁎, Bjørn-Steinar Sæther a, Steinar Skybakmoen b, Christian Uhlig c, Espen Haugland c a b c
Nofima, N-9291 Tromsø, Norway Fishfarming Technology, N-9500 Trondheim, Norway Bioforsk, Norwegian Institute for Agricultural and Environmental Research (Bioforsk), Arctic Agriculture and Land Use Division, N-9269 Tromsø, Norway
a r t i c l e
i n f o
Article history: Received 28 January 2008 Received in revised form 30 October 2008 Accepted 31 October 2008 Keywords: Photoperiod Growth Arctic charr Salvelinus alpinus
a b s t r a c t This study investigates how simulation of condensed winter light conditions effects the growth of wild caught Arctic charr (Salvelinus alpinus L.) held in culture. After capturing from Altevatn, Northern Norway, juvenile Arctic charr were cultivated and subsequently individually divided into two groups. The fish were held under identical conditions from May to October including continuous light. Starting from week 41 after capture (October) one group was subjected to a winter light regime of 6 h light and 18 h dark per day (Winter Light group—WL), while light regimes in the second group remained continuous (Light group). After an eight weeks treatment period the WL-group was reverted to the continuous light regime until the experiment ended in May 2007. Results revealed no pre-treatment differences in growth between the two groups. However, starting from two months after the short day treatment, fishes from the WL group had significant higher growth rates compared to L group fish. At the end of the experiment, e.g. five months after the light treatment, fishes from WL group had increased their average body weight by 353 g as compared to 252 g in the L group. Consequently, results show that simulation of winter light conditions can increase the productivity of landbased Arctic charr (Salvelinus alpinus L.) cultivation by 25 to 30%. Thus, management of wild caught charr farming, great care should be taken as to what light regimes the fish are exposed to. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Arctic charr (Salvelinus alpinus L.) is the northernmost distributed freshwater fish and is considered the most cold-adapted species within the salmonid family (Johnson, 1980). Growth of Arctic charr populations are known to be highly variable under natural conditions (Johnson, 1980; Hammer, 1984). Due to its distribution, Arctic charr experience considerable seasonal changes in photoperiod throughout the year. The charr seems very well adapted to these changes, enabling the species to utilise the rapid seasonal changes in resource availability in the northern areas (Johnson, 1980). Changes in photoperiod is one of the more rigid environmental cues to the fish with its effects widely studied, and it is particularly known to influence on feeding, growth and maturation of Arctic charr (Mortensen and Damsgård, 1993; Frantzen et al., 2004). In general, food intake and growth of Arctic charr is highest during spring and early summer when day length increase continuously from 0 (polar night) to 24 h (midnight sun) (Tveiten et al., 1996; Kestemont and Baras, 2001; Johnston, 2002). It is the change from short to long day in spring that trigger this shift in
⁎ Corresponding author. Tel.: +47 776 29000; fax: +47 776-29100. E-mail address: Sten.siikavuopio@fiskeriforskning.no (S.I. Siikavuopio). 0044-8486/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2008.10.060
growth potential, rather than the long day per se. As demonstrated by Mortensen and Damsgård (1993), juvenile Arctic charr cultivated under constant short- or long-day conditions grew at comparable rates, while growth rates of fishes that experienced short-day conditions followed by long-day conditions were significant higher. Furthermore, Sæther et al. (1996) suggests that Arctic charr has an endogenous growth and maturation rhythm independent of external photoperiod information, which indicates that their life cycle is genetically adapted to artic light conditions. Basic biorhythm research describes that environmental cues, like photoperiod, serve to synchronise annual endogenous rhythms, and as such, the changes in photoperiod are likely to adjust the endogenous rhythms controlling seasonal events (Gwinner, 1981). The importance of photoperiod on growth and life cycle is not restricted to Arctic charr but applies also to other salmonids. Consequently, photoperiod manipulation is a key tool within salmonid production (Taranger et al., 1999; Bromage et al., 2001; Peterson and Harmon, 2005; Nordgarden et al., 2005). Systematic studies on the effect of abrupt changes in photoperiod on growth in Arctic charr are scarce and little is known about the possibilities of improving productivity through photoperiod manipulation in Arctic charr farms. This study aimed to investigate the effects of a temporarily winter light-regime on growth and production
432
S.I. Siikavuopio et al. / Aquaculture 287 (2009) 431–434
Table 1 Development of SGR, condition factor (K) and survival (S) of Arctic charr (Salvelinus alpinus L.) cultivated at continuous light (L) or simulated winter photoperiod (WL) Time
L (SGR)
WL (SGR)
Time
L (K)
WL (K)
May–June June–Sep. Sep.–Oct. Oct.–Nov. Nov.–Dec. Dec.–Jan. Jan.–Mar. Mar.–May
1.72 (0.02)a 0.90 (0.12)a 0.35 (0.05)a 0.32 (0.07)b 0.10 (0.01)a 0.31 (0.09)a 0.59 (0.08)a 0.42 (0.03)a
1.60 (0.03)a 0.93 (0.07)a 0.45 (0.13)a 0.09 (0.01)a 0.13 (0.03)a 0.46 (0.05)a 0.86 (0.05)b 0.62 (0.02)b
May 2006 Dec.2006 May 2007
1.16 (0.26)a 1.22 (0.18)a 1.28 (0.18)a
1.17 (0.18)a 1.22 (0.18)a 1.39 (0.14)b
L (S)
LW (S)
78%
79%
Different letters denote significant differences (P b 0.05). Data are presented as mean ± S.D.
of a juvenile Arctic charr (Salvelinus alpinus L.) population in a northern Norwegian fish farm.
factor (K) is calculated according to the length–weight relationship as follows; K = 100WLT− 3 where W is the weight of the fish and LT the corresponding total length.
2. Material and methods 2.3. Statistical analysis 2.1. Fish and rearing The wild caught Arctic charr (Salvelinus alpinus L.) used in this experiment originated from lake Altevatn in Bardu (68°N, 19°E). The individual fish weight at the day of capture (5 April 2006) varied between 10 and 25 g. The fish were held in a 4000 l tank at Villmarksfisk in Bardu during the first month. They were weaned to dry feed during a two week period by adding 10% cod roe to the dry feed at day one, and gradually reduce this to 0 addition on day 14. Following weaning the fish were fed formulated dry feed, using a recipe adapted to Arctic charr, (Skretting®, Stokmarknes, Norway). Feed rations were surplus by 20% according to the feed table developed for Arctic charr by Jobling et al., 1993. Following weaning the fish were held at continuous light (24L), with light intensity measured to 150 lx at the water surface (fluorescent lamp) and constant water temperature of 8 °C (±0.5 °C) until the onset of the experiment in May 2006. Two weeks prior to the start of the experiment 200 of totally 1200 fish were anaesthetized using 80 µl l− 1 benzocaine and individually tagged with fingerling tags (Floy-Tag) attached through the musculature just anterior to the dorsal fin. The fish were randomly distributed into four 2000 litre fibreglass tanks, with 50 tagged and 250 untagged fish per tank. The tanks were assigned to two treatment groups in May but kept under identical conditions until October, when photoperiod treatment began. Starting from week 41 after capture (October) fishes in tanks 1 and 3 were given a winter light regime of 6 h light and 18 h dark per day (Winter Light group), while light regimes in tanks 3 and 4 remained unchanged (Light group). After eight weeks with winter light regime group WL were reverted to the 24 h light regime until the end of the experiment in May 2007. Water temperature was kept at 8.0 °C (±0.5 °C ), continuously recorded in the inflow water using EBI-125A, WINLOG 2000-S temperature loggers. Water oxygen and pH levels were measured weekly with Handy Delta logger and Oxygard pH logger, (OxyGuard®), in the tank effluent water; readings throughout the entire experimental period indicated oxygen levels above 80% and pH levels of 7.5 (0.01) at all times. Levels of total ammonia–nitrogen (TAN = 0.66 (0.13) mg/l), nitrite (NO2 = 0.41 (0.11) mg/l), and nitrate (NO3 = 21.5 (4.8) mg/l) were determined two times weekly using Nova 30 spectrophotometer (Spectroquant®).
Data are presented as mean ± standard deviation (S.D.). For statistical analysis STATISTICA™ (StatSoft, 2002) was used. The normal distribution of data were tested using Kolmogorov–Smirnov adapted by Lilliefors and possible statistical differences analysed with a twoway ANOVA. Statistical differences in SGR and K were analysed with a one-way ANOVA. Significance was assumed when P b 0.05. 3. Results During the first 10 months of the growth trial, there were no consistent significant differences in either weight increase or specific growth rate between the two groups. During winter light treatment, the weight increments in the WL group tended to lag behind the continuous light group, and the SGR of WL fish was significantly lower than L fish during the October–November period (Table 1). This tendency changed already one month after the treatment ended (January) and following this point in time, the group that had undergone the winter light period had significantly higher body weight (Fig. 1; F8,18 = 36.627, P = 0.001) and specific growth rate (Table 1; F1,2 = 37.098, P = 0.025) as compared to the group held on continuous light. The SGR were highest during summer
2.2. Measured parameters At the start and the end of the experiment individual length (precision 0.1 cm) and weight (0.5 g) of all Arctic charr was measured. All growth estimates are based on length and weight measurements of the individually tagged fish (total n = 200), which were sampled at day 0, 40, 120, 150, 180, 210, 260, 310 and 360. Specific growth rate (SGR) was calculated according to the formula: SGR = (eg − 1) ⁎ 100, where g = (lnW2 − lnW1)(t2 − t1)− 1 and W2 and W1 are weights (g) at days t2 and t1, respectively. The condition
Fig. 1. Weight increase (gram) of Arctic charr (Salvelinus alpinus L.) reared under cultivated at continuous light (L) or simulated winter photoperiod (WL). The arrow marks the start and the end of the two months short day treatment of group LW. Different letters denote significant differences (P b 0.05).
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right after capturing; declining towards autumn with minimum for WL in October–November, and for L during November–December. The SGR increased during December, January and February, but reduced again by approximately 20% in the period between March and May. The SGR ended markedly lower compared to the period after capture in May– June 2006. The condition factor were significant higher in the WL group at the end of the experiment (F1,2 = 62.581, P = 0.0158) as compared to fish that only experienced continuous light after capture (Table 1).The mortality rates during the 12-month experiment were about 20% and did not differ between groups (Table 1). 4 Discussion 4.1. Growth The growth was identical in both groups between tagging and onset of treatment, providing a good starting point for the experiment. The winter light treatment apparently led to reduced growth performance. However, following the condensed winter, this fish entered what resembles a growth compensation that can be associated with a shift in seasonal changes in growth potential (Sæther et al., 1996; Tveiten et al., 1996). At the end of the experiment, and five months after the different light treatments, fishes from group WL had increased their average total weight by 353 g compared to 252 g of group L. These results show that simulation of natural winter light conditions can increase the subsequent growth rate of Arctic charr, at least temporarily. The growth rate data in this study resembles results obtained on juvenile Arctic charr by Mortensen and Damsgård (1993). The development of the specific growth rate (SGR) showed a clear temporal pattern for both trails. Winter depression with a reduction in SGR from about 1.6% in summer to about 0.1% in late autumn followed by a significant increase in SGR from January to February but stagnation from March to May. Temporal cycling in food intake, growth and body fat stores have been described in several species of animals held under controlled conditions, with species living at high latitudes that appear to exhibit the greatest seasonal fluctuations (Jobling, 1994, Loudon, 1994, Tveiten et al., 1996, Jobling et al., 1998, Oppedal et al., 2006). Sæther et al. (1996) demonstrated that even though environmental factors such as photoperiod and temperature were constant there persist some seasonal changes (indicating endogenous control) of growth in Arctic charr. The changes in specific growth rate pattern in the reported study are similar to results obtained by Sæther et al. (1996). The temporal difference in growth response in these two groups can be due to the “winter” information given only to the WL group, adjusting their internal rhythm to proceed to spring conditions when day length again increased (Gwinner, 1981). Endocrine control is involved in growth and there is information on the direct effect of light on the release of several hormones, mainly growth and thyroid hormones (Jobling, 1994, Boeuf and Le Bail, 1999, Evans and Claiborne, 2006). However, the seasonal timing effect of photoperiod may act stronger on the growth performance, as is also seen in this trial. For production management it is important to realise that effects of light on consecutive growth depend on the physiological state of the animal when received, and manipulation of photoperiod should be used with great care to gain the planned result (Gwinner, 1981). Endogenous rhythms are only receptive to environmental stimuli that is in accordance with the time phase they are in, e.g. manipulation should aim at condensing, stretching or phase shift seasons, not jump them. 4.2. Mortality The accumulated mortality was about 20% for both light treatments at the end of the experiment. However, mortality was highest during the first 90 days of cultivation. The absence of food in the stomach of the majority of the dead fish, suggest that they had been
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unable to adapt to indoor cultivation conditions, including weaning to dry feed. However, overall mortality between the two different light treatments did not differ, indicating comparable physical, chemical and biological conditions between the groups. 4.3. Conclusion and perspectives This results clearly indicate that better growth were obtained in Arctic charr that received a winter light stimuli, for 8 weeks (6L: 18D) compared to Arctic charr reared under continuous light. This winter stimuli came after a period with continuous light, when the fish is expecting and receptive to a winter signal. Consequently, results show that simulation of condensed winter light conditions can increase the productivity in land-based Arctic charr cultivation by at least 25 to 30%. Use of changes in photoperiod should therefore gain more attention in production management processes. It is important to realise the limitations involved, and that the changes are likely to be temporal. Further studies on seasonality and growth in Arctic charr culture is are needed to fully understand the importance of endogenous rhythms controlling feeding, growth and maturation and how to utilise them to their potential. Acknowledgements The Norwegian Research Council, project no. 167941/110, supported this study. We would also like to thank Dagfinn Lysne and Nils Steien at VillmarksFisk for their technical assistance and advice on this work. References Boeuf, G., Le Bail, P.-Y., 1999. Does light have an influence on fish growth? Aquaculture 177, 129–152. Bromage, N., Porter, M., Randall, C., 2001. The environmental regulation of maturation in farmed finfish with special reference to the role of photoperiod and melatonin. Aquaculture 197 (1–4), 63–98. Evans, D.H., Claiborne, J.B., 2006. The Physiology of Fishes. Third edition, CRC Press, Taylor & Francis Group. 602 pp. Frantzen, M., Arnesen, A.M., Damsgård, B., Tveiten, H., Johnsen, H.K., 2004. Effects of photoperiod on sex steroids and gonad maturation in Arctic charr. Aquaculture 240 (1–4), 561–574. Gwinner, E., 1981. Circannual systems. In: Aschoff, J. (Ed.), Handbook of Behavioural Neurobiology volume 4 Biological Rhythms. Plenum press, New York, pp. 391–410. Hammer, J., 1984. Ecological characters of different combinations of sympatric populations of Arctic charr in Sweden. In: Johnson, L., Burns, B.L. (Eds.), Biology of the Arctic Charr. Proceedings of the International Symposium of Arctic Charr, Winnipeg, Manitoba, May 1981. University of Manitoba Press, Winnipeg. 35–63 pp. Jobling, M., 1994. Fish Bioenergetics. Chapman and Hall, London. 309 pp. Jobling, M., Jørgensen, E.H., Arnesen, A.M., Ringø, E., 1993. Feeding, growth and environmental requirements of Arctic charr: review of aquaculture potential. Aquaculture international 1, 20–46. Jobling, M., Tveiten, H., Hatlen, B., 1998. Cultivation of Arctic charr: an update. Aquaculture international 6, 181–196. Johnson, L., 1980. The Arctic charr, Salvelinus alpinus. In: Balon, E.K. (Ed.), Charrs, Salmonid Fishes of the Genus Salvelinus. W. Junk, The Hague, Netherlands. 87 pp. Johnston, G., 2002. Arctic Charr Aquaculture. Blackwell Publishing. 272 pp. Kestemont, P., Baras, E., 2001. Environmental factors and feed intake: mechanisms and interactions. In: Houlihan, D., Boujard, T., Jobling, M. (Eds.), Food Intake in Fish. Blackwell Science Ltd. 131–156 pp. Loudon, A.S.I., 1994. Photoperiod and the regulation of annual and circannual cycles of food intake. Proceeding of the Nutrition Society 53, 495–507. Mortensen, A., Damsgård, B., 1993. Compensatory growth and weight segregation following light and temperature manipulation of juvenile Atlantic salmon (Salmon salar L.) and Arctic charr (Salvelinus alpinus L.). Aquaculture 114, 261–272. Nordgarden, U., Hansen, T., Hemre, G.I., Sundby, A., Björnsson, B.T., 2005. Endocrine growth regulation of adult Atlantic salmon in seawater: the effects of light regime on plasma growth hormone, insulin-like growth factor-I and insulin levels. Aquaculture 250, 862–871. Oppedal, F., Berg, A., Olsen, R.E., Taranger, G.L., Hansen, T., 2006. Photoperiod in seawater influence seasonal growth and chemical composition in autumn seatransferred Atlantic salmon (Salomo salar L.) given two vaccines. Aquaculture 254, 396–410. Peterson, R.H., Harmon, P.R., 2005. Changes in condition factor and gonadosomatic index in maturing and non-maturing Atlantic salmon (Salmo salar L.) in Bay of Fundy sea cages, and the effectiveness of photoperiod manipulation in reducing early maturation. Aquaculture Research 36 (9), 882–889.
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