Natural Photoperiod Group Research Articles

Effect of photoperiod on growth, survival, and lipid metabolism of mud crab Scylla paramamosain juveniles

Photoperiod is one of the most important environmental cues for the organism, and it plays a critical role in regulating organisms' survival, growth, and metabolism. In the present study, the effects of photoperiod (0 L∶24 D, 6 L∶18 D, 12 L∶12 D, 18 L∶6 D, and 24 L∶0 D) on mortality, growth performance, and lipid metabolism of juvenile mud crab (Scylla paramamosain) were studied with an 8-week experiment. The results showed that the highest final weight of crabs was observed in the 18 L∶6 D (0.48 ± 0.08 g), which was significantly higher than 0 L∶24 D (0.22 ± 0.03 g) and 6 L∶18 D (0.28 ± 0.04 g) (P < 0.05). In addition, the specific growth rate (SGR) of crabs reared at 12 L∶12 D (natural photoperiod) (5.83 ± 0.26% day−1) and 18 L∶6 D (6.28 ± 0.27% day−1) were significantly higher than 0 L∶24 D (4.70 ± 0.42% day−1), 6 L∶18 D (5.16 ± 0.22% day−1) and 24 L∶0 D (5.60 ± 0.23% day−1) (P < 0.05). The survival rate of the natural photoperiod group was significantly higher than 18 L∶6 D group (69.23 ± 6.28% vs 35.90 ± 3.63%) (P < 0.05), but no significant difference between 0 L∶24 D (58.97 ± 3.63%), 6 L∶18D (66.67 ± 7.25%) and 24 L∶0 D (58.97 ± 7.25%) groups was observed (P > 0.05). Crabs exposed to 18 L∶6 D photoperiod also had higher melatonin (311.12 ± 79.53 pg mL−1 vs 168.79 ± 31.24 pg mL−1) and cortisol levels (451.37 ± 237.64 ng mL−1 vs 112.91 ± 39.32 ng mL−1) than those reared in constant light (24 L∶0 D) (P < 0.05). In addition, compared with natural photoperiod, crabs reared under constant darkness showed significantly higher TG and TC content (P < 0.05). Moreover, in constant darkness, lipogenesis-related genes such as fatty acid synthase (fas), sterol regulatory element binding protein-1 (srebp-1), and acetyl-CoA carboxylase (acc) of the crab were up-regulated, and lipolysis-related genes as carnitine palmitoyltransferase-1 (cpt-1), Acyl-CoA oxidase-3 (aco-3) were significantly down-regulated (P < 0.05). Besides, fatty acid binding protein (fabp) was also up-regulated in crabs reared under constant darkness. Thus, these results suggest that the crabs in constant darkness did not effectively utilise the lipid as an energy source. Overall, the present research confirmed that light cues are indispensable for the indoor mud crab culture system, and the natural photoperiod was recommended for mud crab during the juvenile grow-out phase in commercial operations.

Effect of Photoperiod Manipulation on Spawning Time and Performance of Turbot (Scophthalmus maximus)

Temperature and photoperiod are known as the main stimuli of seasonal reproduction in fish. Turbot (Scophthalmus maximus) is a spring spawning teleost fish species with a promising aquaculture potential and high market value. This study was conducted to assess the effect of photoperiod manipulation on spawning time and spawning performance of turbot. A total of 28 mature turbots from the Black Sea population were subjected to manipulated photoperiod (a photoperiod regime that fish would naturally receive three months later) and natural photoperiod for almost a year. While the fish exposed to natural photoperiod spawned in May, the fish exposed to manipulated photoperiod spawned almost three months earlier compared to the natural photoperiod group. Reproductive and hatchery performance of the manipulated photoperiod and natural photoperiod groups were similar. It can be emphasized that photoperiod play an important role in accelerating maturation and spawning. The findings of this study could be implemented in the turbot aquaculture industry to advance production.

Possible Involvement of Photoperiodic Regulation in Reproductive Endocrine System of Female Olive Flounder Paralichthys olivaceus

ABSTRACTThis study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-β, LH-β and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-β, LH-β and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-β, LH-β and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.

Possible Involvement of Photoperiodic Regulation in Reproductive Endocrine System of Female Olive Flounder Paralichthys olivaceus.

This study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-β, LH-β and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-β, LH-β and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-β, LH-β and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.

Long Photoperiod Affects Gonadal Development in Olive Flounder Paralichthys olivaceus.

To effects of sex maturation in olive flounder by regulating long photoperiod, gonadal development and GTH mRNA expression in the pituitary were investigated. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from September 2011 to March 2012. The results showed that natural photoperiodic group showed a higher gonadosomatic index (GSI) than long photoperiodic group during the spawning season (March 2012). The histological analysis of ovarian tissue showed that natural photoperiod group of ovaries contained vitellogenic oocytes, but long photoperiod group of ovaries mainly contained perinucleolus staged oocyte and oil-drop staged oocytes. The FSH mRNA of olive flounder, under natural photoperiod group, showed a significantly higher expression but no significant difference under long photoperiod group. The LHβ mRNA showed a significantly higher expression only under natural photoperiod group. These results may suggest that long photoperiodic information regulates secretion of pituitary FSH and LH and maintain early growing stage of gonadal development in this species.

Photoperiod Influences Growth and mll (Mixed-Lineage Leukaemia) Expression in Atlantic Cod

Photoperiod is associated to phenotypic plasticity of somatic growth in several teleost species. However, the molecular mechanisms underlying this phenomenon are currently unknown but it is likely that epigenetic regulation by methyltransferases is involved. The MLL (mixed-lineage leukaemia) family comprises histone methyltransferases that play a critical role in regulating gene expression during early development in mammals. So far, these genes have received scant attention in teleost fish. In the present study, the mean weight of Atlantic cod juveniles reared under continuous illumination was found to be 13% greater than those kept under natural photoperiod conditions for 120 days. We newly determined cDNA sequences of five mll (mll1, mll2, mll3a, mll4b and mll5) and two setd1 (setd1a and setd1ba) paralogues from Atlantic cod. Phylogenetic analysis revealed that the cod genes clustered within the appropriate mll clade and comparative mapping of mll paralogues showed that these genes lie within a region of conserved synteny among teleosts. All mll and setd1 genes were highly expressed in gonads and fast muscle of adult cod, albeit at different levels, and they were differentially regulated with photoperiod in muscle of juvenile fish. Following only one day of exposure to constant light, mll1, mll4b and setd1a were up to 57% lower in these fish compared to the natural photoperiod group. In addition, mRNA expression of myogenic regulatory factors (myog and myf-5) and pax7 in fast muscle was also affected by different photoperiod conditions. Notably, myog was significantly elevated in the continuous illumination group throughout the time course of the experiment. The absence of a day/night cycle is associated with a generalised decrease in mll expression concomitant with an increase in myog transcript levels in fast muscle of Atlantic cod, which may be involved in the observed epigenetic regulation of growth by photoperiod in this species.

Growth and blood chemistry of Atlantic halibut (Hippoglossus hippoglossus L.) in relation to salinity and continuous light

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.

Reduction of sexual maturation in male Dicentrarchus labrax by continuous light both before and during gametogenesis

The objective of this study was to investigate the effect of exposure to continuous light (LL) during the pregametogenesis (4-month duration) and gametogenesis (6-month duration) periods on early male sexual maturation in the sea bass. A simulated natural photoperiod group (SNP) and a long-term exposure group to LL during 12 months were kept as controls. Somatic growth, gonadal development, plasma testosterone (T) and 11-ketotestosterone (11-KT) and the expression of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary were analysed as indicators of maturation. Growth in all treatments was independent of photoperiod. Nevertheless, all LL treatments were effective in reducing the number of early maturing males (<3% with <0.2% GSI versus 22% with 0.8% GSI in SNP). This inhibition was not complete but the effect was comparable among all LL treatments thus suggesting that a potential photo-labile period might exist in the sea bass. In the SNP group, the T and 11-KT plasma levels as well as the gene expression values of the three gonadotropin subunits (i.e., LHβ, FSHβ and glycoprotein (GP) α) peaked in February concomitantly with the increase of the GSI (≥0.51%) and the accumulation of LH protein in the pituitary (≥14.6 μg) and declined at post-spermiation stage (GSI≤0.12% and LH protein≤10.2 μg/pit). Exposure to different LL treatments induced a differential response particularly on the 11-KT levels and the gene expression of the FSHβ subunit. We suggest that the unbalanced production of this androgen regulated by FSHβ might be limiting the stimulation of germ cell proliferation at the testicular level and thus arresting early puberty male sea bass.

Chilled storage of semen from Atlantic halibut, Hippoglossus hippoglossus L. II: Effect of spermiation advancement, catheterization of semen, and production-scale application

A method for in vitro storage of Atlantic halibut Hippoglossus hippoglossus L. semen can facilitate seed production. The study aimed at determining the effect of male spermiation advancement on viability of chilled stored spermatozoa. The use of catheterization of semen from the sperm duct was examined. Also, large volumes of semen were stored under sub-optimal production-like conditions in order to determine the suitability of the method into practical use. Semen was collected from two broodstocks: natural photoperiod males, being at the first phase of the reproductive season and 3-month advanced photoperiod males, being at the end of the reproductive season. Semen samples were diluted 1:5 (v/v) with modified Hanks’ Balanced Salt Solution supplemented with antibiotics, and stored in Ziploc bags filled with air. Sperm motility parameters, assessed by computer-assisted sperm analysis (CASA), were assessed weekly. Experimental and production-scale fertilization trials were performed. Sperm samples from natural photoperiod males showed significantly longer viability under in vitro storage conditions than sperm from advanced photoperiod males. In the natural photoperiod group, the decrease in spermatozoa motility, curvilinear velocity and straight-line velocity occurred on day 50, 14, and 28 of storage, respectively. Spermatozoa from one of five males were still motile on day 80 of storage, and fertilization rates and embryo survival rates obtained using semen stored for 70 days did not differ from control values and they were significantly higher than values obtained with the use of fresh semen of the same male, but being at the end of reproductive season. Catheterization of semen showed no advantage to stripping the semen without a catheter, even for samples stored undiluted for 1 day of collection, before dilution. Under sub-optimal conditions, spermatozoa stored in large volumes (10–100 mL of diluted semen) without any special treatments except for weekly swirling, remained viable for more than 1 month. Production-scale fertilizations with samples stored for 5–21 days resulted in high survivals of embryos and hatchlings. Because of its simplicity and efficiency, the method shows a high potential for use in commercial Atlantic halibut farming. It has already been applied to a halibut breeding programme for the next reproductive season at our research station.

Growth, gonadal development and spawning time of Atlantic cod ( Gadus morhua) reared under different photoperiods

Individually tagged Atlantic cod ( Gadus morhua L .) (mean body weight 459±6 g) were reared in 20-m 3 tanks supplied with running sea water. During the first year the fish were exposed to one of four photoperiod regimes: Natural light (LDN), continuous light from June 23, 1993 (LL), natural light from June 23, 1993 and continuous light from December 22, 1993 (LDN/LL) or continuous light from June 23, 1993 and natural light from December 22, 1993 (LL/LDN). In July 1994, the LDN and LDN/LL groups were terminated. The LL and LL/LDN groups were reared on until May 1995. From July 1994 to the termination of the experiment in May 1995, the LL group was reared under continuous light and the LL/LDN group was reared under natural photoperiod. Cod reared under natural photoperiod spawned in the period between January and April. Photoperiod manipulation changed the incidence of sexual maturation, spawning time, fecundity and egg size. Cod that were transferred from natural photoperiod to continuous light in December spawned earlier, having lower fecundity and smaller eggs than the cod reared under natural photoperiod. Oocytes of females reared under continuous light were arrested in the cortical alveoli stage, and even in their second year on continuous light very few females matured. When transferred to natural photoperiod in December, females ovulated within 4–5 months, approximately 3 months delayed compared to the natural photoperiod group. These cod had a higher fecundity and smaller eggs than natural photoperiod cod. When reared on for another year under natural photoperiod these cod spawned again the next year at their normal spawning time, e.g. 9 months after their first spawning. The pattern of sexual maturation influenced the somatic growth pattern. Differences in growth were explained by differences in the timing of the spawning and the relative spawning investment. At an age of 26 months, the weight of the cod reared under natural photoperiod and continuous light were 1.5 and 2.5 kg, respectively. From this, it is concluded that a reduction in daylength is a vital environmental signal regulating the maturation and spawning of cod, and that sexual maturation may be arrested or considerably delayed in its absence.

Development and validation of an enzyme immunoassay for testosterone: effects of photoperiod on plasma testosterone levels and gonadal development in male sea bass (Dicentrarchus labrax, L.) at puberty.

A specific immunoassay was developed for the quantification of testosterone (T) in sea bass plasma. Specific primary antibody against T was produced using an antigen BSA conjugated with T. The enzyme immunoassay (EIA) had a sensitivity of 5–0.009 ng ml−1 and 6.2% intra-assay variation; inter-assay variation was 9.5% for sea bass plasma. The effects of two different accelerating photoperiod regimes, compressed photoperiod (CO; 6 months), and constant short photoperiod (9L:15D) with a long photoperiod (15L:9D) in March (SLmar), on T plasma levels and sexual maturation were examined during the onset of puberty in male sea bass. Natural photoperiod (NP) and SLmar groups exhibited the highest T values in December (8.69±1.03 and 10.85±1.04 ng ml−1, respectively). However, SLmar group showed the first significant decrease in T plasma levels in January, two months earlier than the NP group, which presented elevated T levels until February. The CO group displayed two significant T peaks, one in October (8.90±1.60 ng ml−1) and the other in January (9.60±1.10 ng ml−1). Gonadosomatic index (GSI) in the NP and SLmar groups displayed the highest values from December to February (>2.5%). However, the SLmar group showed the first significant increase in GSI in November, one month before the controls, indicating a clear advancement of gonadal development with respect to the NP group. In the CO group, a bimodal pattern was observed with two peaks, one in October–November (1.30±0.25%) and the second in March–April (0.97±0.33%) (P<0.05). In NP group, the percentage of running males was about 80% from December to March while the percentage of running males in the SLmar group (∼70%) lasted only three months (December to February) decreasing (P<0.05) in March. In the CO group, spermiation began in October (60%), decreased during the next months, and increased again in March–April (30%) (P<0.05). These results indicate the advancement of puberty by either one or two months with respect to the control group in the SLmar and CO groups, respectively, and the presence of a second reproductive surge in the CO group. Collectively, these results suggest that exposure of fish to these photoperiod regimes may affect both the time of the onset of puberty and the pattern of gonadal development in prepuberal male sea bass.

Effect of Three Hatchery Lighting Schemes on Indices of Smoltification in Chinook Salmon

Abstract This experiment examined whether photoperiodic changes induce chinook salmon Oncorhynchus tshawytscha to alter various indices of smoltification. The effect of 24 h light, a constant photoperiod of 9 h light: 015 h dark (9L:15D), and a naturally increasing photoperiod on plasma levels of thyroxine and cortisol, hematocrit, condition factor (K), and hepatosomatic index (HSI) was tested during the period of smoltification in chinook salmon. The 24-h-light group grew faster than the other two groups, but was significantly larger than one of the two groups on only three sampling dates. Mean plasma thyroxine and cortisol levels were highest in the natural-photoperiod group and lowest in the 9L:15D group. Mean plasma cortisol levels increased significantly in the increasing and 9L:15D photoperiod groups but were unchanged in the continuous-light group. Mean HSI decreased faster in the natural-photoperiod group than in the other two groups. Mean hematocrit did not change in the natural-photoperiod group...

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula)

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.

First feeding of Atlantic salmon, Salmo salar L., under different photoperiods and light intensities

. First feeding fry of Atlantic salmon, Salmo salar L., were reared under four experimental light regimes from mid-June until mid-September. One group was reared under a simulated natural photoperiod 4 months out of phase, with initial daylength in mid-June corresponding to natural daylength in mid-February. Two groups were reared under continuous light of either low (27 lux) or high (1400 lux) intensity. The fourth group received a dual photoperiod combining a continuous, low intensity (27 lux) background illumination and a superimposed simulated natural photoperiod phase adjusted according to the natural photoperiod group. Growth rate and survival was higher during the first 3 weeks under continuous light or dual photoperiod than under the phase adjusted simulated natural photoperiod. This could partly be due to the restricted feeding time during the initial short daylength of the simulated natural photoperiod, and partly to a photostimulation of growth in groups reared under the continuous light regimes. Fish reared under a simulated natural photoperiod migrated vertically during the 24-hour cycle. The same behaviour was seen, though not as ctearly, in the fish reared under a dual photoperiod. Changes in light intensity appeared to be the primary releasing factor for the vertical migration observed. The fish reared under continuous light showed no diurnal vertical migration. Acknowledgments The authors would like to thank Dr Gunnar Naevdal and Dr Lars Petter Hansen for helpful suggestions and criticism of the manuscript. We also thank the staff at Matre Aquaculture Station for skilled assistance during the experiment. This study was financed by the Norwegian Fisheries Research Council (NFFR V.701.146).

The seasonal cycle of body weight in the Djungarian hamster: photoperiodic control and the influence of starvation and melatonin

Photoperiod is the primary environmental cue for seasonality in the Djungarian hamster (Phodopus sungorus). This species reduces its body weight by 30% during winter to reduce its energy requirements. The aim of this study was (1) to examine the influence of food intake on the body weight cycle and (2) to evaluate the role of photoperiod and melatonin in determining this seasonal cycle.While body weight increased slightly (7%) from August through December in long photoperiod, it dropped significantly (32%) in the natural photoperiod group and food intake gradually decreased in this group by about 20%. After two periods of 40% food restriction, the hamsters in long photoperiod rapidly returned to their initial body weight. In contrast, hamsters under natural photoperiod only gained weight until they had reached the body weight of the controls at that particular time.In a second experiment, hamsters were kept under natural photoperiod throughout the year. At 6 different intervals two groups of hamsters were implanted with melatonin capsules and transferred to either short (LD 8:16) or long photoperiod (LD 16:8). The results show that the seasonal change in body weight is caused by a combined action of photoperiod and a change in the animals' sensitivity towards photoperiod and melatonin.