Continuous Light Regime Research Articles

PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1A redox states alleviate photoinhibition during changes in light intensity.

Plants have evolved photosynthetic regulatory mechanisms to maintain homeostasis in response to light changes during diurnal transitions and those caused by passing clouds or by wind. One such adaptation directs photosynthetic electron flow to a cyclic pathway to alleviate excess energy surges. Here, we assign a function to regulatory cysteines of PGR5-like protein 1A (PGRL1A), a constituent of the PROTON GRADIENT REGULATION5 (PGR5)-dependent cyclic electron flow (CEF) pathway. During step increases from darkness to low light intensity in Arabidopsis (Arabidopsis thaliana), the intermolecular disulfide of the PGRL1A 59-kDa complex was reduced transiently within seconds to the 28-kDa form. In contrast, step increases from darkness to high light stimulated a stable, partially reduced redox state in PGRL1A. Mutations of 2 cysteines in PGRL1A, Cys82 and Cys183, resulted in a constitutively pseudo-reduced state. The mutant displayed higher proton motive force (PMF) and nonphotochemical quenching (NPQ) than the wild type (WT) and showed altered donor and acceptor dynamic flow around PSI. These changes were found to correspond with the redox state of PGRL1A. Continuous light regimes did not affect mutant growth compared to the WT. However, under fluctuating regimes of high light, the mutant showed better growth than the WT. In contrast, in fluctuating regimes of low light, the mutant displayed a growth penalty that can be attributed to constant stimulation of CEF under low light. Treatment with photosynthetic inhibitors indicated that PGRL1A redox state control depends on the penultimate Fd redox state. Our results showed that redox state changes in PGRL1A are crucial to optimize photosynthesis.

Modeling Approach to Capture the Effect of High Frequency Flashing Light in Steady-State Microalgae Cultures

With the advent of efficient artificial light systems, the possibility of exploiting pulsed light (PL) in microalgal cultivation is gaining renewed attention. In this work, a model was developed to describeArthrospira maxima production in continuous cultivation systems, under both continuous and high-frequency pulsed light regimes. The model is based on the one originally developed by Camacho-Rubio, modified to link photosynthetic units activation to biomass growth, accounting also for maintenance. The modified model, calibrated in continuous light regime, was found to properly predict steady-state microalgal growth at different light intensities and residence times. The model was then validated on experimental data carried out under extreme PL conditions (high frequencies up to 3700 Hz and duty cycles as low as 0.01). Remarkably, it was able to account for the flashing light effect (FLE, i.e., increased biomass production with respect to continuous light supply) measured under such conditions and can therefore be a valuable tool to optimize the energetic efficiency of algal cultivation.

The effect of light regime and time of slaughter in broiler on broiler performance, liver antioxidant status, and expression of genes related to peptide absorption in the jejunum and melatonin synthesis in the brain.

This study aimed to assess the effects of light regime and time of slaughter on primal cut and organ weights, peptide transporter 1 (PEPT1) gene expression in the jejunum, arylalkylamine N-acetyltransferase (AANAT) gene expression in the brain, and liver oxidant/antioxidant status in broilers aged 37 days. The experiment was conducted in a factorial completely randomized design, with two light regimes (intermittent light varying according to bird age and continuous light under an 18 h light/6 h dark photoperiod) and four times of slaughter (2:00, 8:00, 14:00 and 20:00 h). There was an interaction effect on PEPT1 and AANAT expression, lipid and protein oxidation and superoxide dismutase (SOD) activity. In both light regimes, PEPT1 expression responded cubically to slaughter time. In the continuous light group, PEPT1 expression was highest in birds slaughtered at 2:00 and 14:00 h, whereas, in the intermittent light treatment, expression was highest at 8:00 h. In the continuous light regime, AANAT expression had a cubic relationship with time of slaughter, with the greatest values recorded at 20:00 h. In the intermittent light regime, slaughter time showed a cubic effect on lipid oxidation, which was highest at 8:00 h. In the continuous light group, there was a cubic effect on nitrite concentration, lipid oxidation, protein oxidation, and SOD activity; nitrite levels, lipid oxidation, and protein oxidation were highest and SOD activity was lowest in birds slaughtered at 14:00 h. Time of slaughter influenced catalase activity, which responded cubically; catalase activity was lowest at 8:00 and 14:00 h. This study is the first to demonstrate that PEPT1 expression in the jejunum of broilers follows a diurnal rhythm and varies according to light regime. The results also suggest that mainly continuous lighting and slaughter at 14:00 h when the animals are possibly more active may be more stressful to broilers.

Differential action of androgen implants on the spermatogenesis of pre-pubertal sea bass exposed to a continuous light regime

This study investigated the influence of long-term T and 11-KT administration (by means of an implant) on the synthesis and release of gonadotropins (Fsh, Lh) and spermatogenesis progression in juvenile male sea bass exposed to either a natural photoperiod (NP) or continuous light (LL). The results in the control group indicated a clear role for Fsh and 11-KT in the recruitment of type-A spermatogonia (SPGA) towards more advanced stages of spermatogenesis under the NP regime. Fsh promoted androgen synthesis and SPGA differentiation into spermatocytes, while no significant changes in pituitary Gnrh1 and plasma Lh levels were detected. On the other hand, the LL regime inhibited Fsh synthesis, and although no effects were observed on Gnrh1 and Lh, the progression of spermatogenesis was arrested. T and 11-KT administration increased the Gnrh1 and Lh content and reduced the pituitary Fsh content, regardless of the photoperiod regime, although the inhibitory effect of T on pituitary Fsh was stronger than that of 11-KT. Our results show that exogenous 11-KT administration in fish under the LL regime was able to partially restore the progression of spermatogenesis, thus stimulating gonadal development and eliciting spermiation in a few fish, while males that received T implants remained sexually immature under LL. In addition, our results provided new knowledge about the importance of Fsh bioactivity modulation in the regulation of this gonadotropin function, and in turn, on spermatogenesis control in fish.

The Effect of Non-Circadian Photoperiod on Growth and Puberty Onset of Brook Trout Salvelinus fontinalis Mitchill.

Simple SummaryThere has been intensive research addressing the positive effects of different prolonged photoperiods on wide spectrum of aspects of salmonids aquaculture. The present study was an attempt to assess non-circadian photoperiod regimens on growth and puberty onset of brook trout. We found regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light to be remarkably effective on the delay of gonad development and onset of puberty, enabling fish farmers to fight with negative aspects related to brook trout puberty.The aim of the present study was to assess the effects of a prolonged photoperiod on growth rate and sexual maturation in brook trout Salvelinus fontinalis. The task of the experiment was to determine the most effective light regimen capable to minimizing the effects of puberty, including impairment of somatic growth and further general characteristics. In this regard, the studied fish were reared under three photoperiod regimens in which fish were exposed to 24 h continuous light alternating with 24 or 48 h under the ambient photoperiod or 48 h continuous light alternating with a 24 h ambient photoperiod. A control group was reared under the natural ambient photoperiod. Four-hundred and fifty fish with an average initial body weight of 101.3 ± 1.2 g were used for each experimental group (three replicates of each treatment plus control). A statistically lower growth rate showed control groups in both sexes. At the end of the study, control males had an average body weight of 226.6 ± 39.8 g and control females a body weight of 199.8 ± 12.2 g. At the same period, a significantly higher average body weight was found in groups reared 24 h under ambient photoperiod alternating with a 48 h continuous light regime (2CP:1AP) in both sexes (296.56 ± 62.5 g—males, and 239.9 ± 19.2 g—females, respectively). A significantly higher percentage of sexually mature fish was observed in the control group (80% of males and 29% of females, respectively). We found significantly fewer sexually mature females compared to males. The lowest survival was observed in group 2CP:1AP at 92%. It was concluded that regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light (1CP:2AP) lead to the successful delay of gonad development and onset of puberty and increased somatic growth in both sexes.

Effects of different light durations during incubation on hatching, subsequent growth, welfare, and meat quality traits among three broiler strains.

Present study was aimed to evaluate the hatching traits and subsequent performance of broilers strains under the intermittent and continuous light regime during incubation. In total, 2250 eggs from Hubbard classic, Cobb-500, and Ross-308 strains (750 eggs from each of same age breeders) were incubated under three different light durations. First treatment was the incubation totally under darkness where no light was able to penetrate in the assigned section of machine. In the second treatment, eggs were incubated at 12h of lightness and 12h of darkness. In the third treatment, the eggs received lightning of 24h. Data were collected for hatching traits and hatch window, growth performance, welfare aspects, and meat quality. A two-way factorial analysis was performed using SAS software applying Duncan's multiple range test. The results showed that hatching traits were improved when Hubbard breeder eggs were provided with light period of 12h. However, gait score was non-significantly different among the treatment. The meat quality was better in Hubbard broilers obtained after 12h of intermittent light during incubation. Blood biochemistry was also improved in Hubbard broilers of 12h of light duration. It was concluded that 12h of light period during incubation is beneficial for getting better hatchability and subsequent performance of Hubbard broilers.

The effect of photoperiod on growth and spawning performance of zebrafish, Danio rerio

This study was conducted to assess the effects of photoperiod on growth and spawning of zebrafish. Two hundred and forty zebrafish (120 males and 120 females) were maintained under four different light dark cycles: shortened light regime (08L:16D), control (12L:12D), extended light regime (16L:08D), and continuous light regime (lights on continuously for 24 h). The fish were kept in these conditions for 42 days, during which growth and reproduction were measured. The best growth was achieved at the ELR group, with the greatest final mean weight (P < 0.05). Zebrafish cultured in 24L:00D produced significantly more larvae than those in 08L:16D at 34th days (P < 0.05). A higher hatching rate was observed in 16L:08D compared to the other groups (P < 0.05). The percentage of ovulated zebrafish females was significantly higher in 16L:08D than in the other groups (P < 0.05). The outcome indicates that extending day length affects both growth and spawning of zebrafish. Together, these data suggest that a photoperiod of 16L:08D might be optimal for laboratory zebrafish, at least from a production standpoint.

A comprehensive circuit model for evaluating the response of silicon photomultipliers in continuous wave light regime

SummaryIn this paper, a comprehensive dynamic model for silicon photomultiplier (SiPM) detectors is proposed to investigate their response when exposed to the light of any wavelength and relatively high intensity. Also, a procedure is proposed to perform reliable circuit‐level simulations to predict the response of these detectors under various photon rates. The approach of dynamic model is based on the state of microcells in terms of overvoltage, elapsed recharging time, and their effect on the triggering probability with which the detector current and voltage can be accurately simulated. Using the proposed model, the SiPM behaviour is examined under various continuous illumination power in simulation. The effectiveness of the proposed model and the simulation method are verified by experimental results extracted from two SiPM detectors.

Reductive capabilities of different cyanobacterial strains towards acetophenone as a model substrate – Prospect of applications for chiral building blocks synthesis

Bioreductive capabilities of four morphologically different strains of cyanobacteria have been assessed in this work. Arthrospira maxima, Leptolyngbya foveolarum, Nodularia sphaerocarpa and Synechococcus bigranulatus were applied as catalysts for the reduction of acetophenone to the corresponding chiral phenylethyl alcohol. The process was modified regarding substrate concentration, duration of pre-cultivation period, duration of biotransformation, light regime and glucose addition to the culture media. Obtained results clearly showed that cyanobacteria were active towards acetophenone what resulted in the substrate reduction to (S)-1-phenylethanol with high enantiomeric excess. The reaction efficiency increased with the biotransformation time, but the higher concentration of substrate limited the process yield. Also, all tested strains performed reaction with the highest efficacy under continuous light regime. The most active strains – N. sphaerocarpa and S. bigranulatus carried out the conversion of 1 mM acetophenone with high efficiency of respectively 97.6% and 96.2% after 13 days of biotransformation. A. maxima reached 45.8% of conversion after 13 days of biotransformation whereas L. foveolarum did not exceed 20%. The enantiomeric excesses were respectively 98.8%- A. maxima, 91.7%- L. foveolarum, 72.6%- S. bigranulatus and N. sphaerocarpa 16.2%.

Diversity among Isolates of the Tangerine Pathotype of &amp;lt;i&amp;gt;Alternaria alternata&amp;lt;/i&amp;gt;

The tangerine pathotype of Alternaria alternata is the aetiological agent of Alternaria brown spot on tangerines. In the state of Paraíba, Brazil, its occurrence on “Dancy” tangerine trees is associated with genetic aspects as well as the influence of environmental conditions on reproduction and dissemination within and between populations. The aim of the present study was to evaluate the diversity of isolates of this pathogen using morphophysiological and molecular markers. For the analysis of mycelial growth and sporulation, 30 isolates from different locations were examined at 24-hour intervals until the seventh day, when the spores were quantified. The 30 isolates were characterised based on molecular markers (ISSR) and genetic similarity (Jaccard index). A factor arrangement was used: 30 isolates, four media (ODA, PDA, LEA and V8), three light regimes (continuous dark, alternating light and continuous light) and three temperatures (15°C, 25°C and 35°C), with 12 repetitions. Groups 1, 2 and 3 presented low genetic variability. Group 4 showed high genetic variability of the isolates obtained from the Massaranduba (state of Paraíba-Brazil) producing region and higher mycelial growth and sporulation of A. alternata. The continuous light regime and the temperature 25°C in PDA and V8 media were the ideal conditions for the mycelial growth and sporulation, respectively, of the isolates of A. alternata.

The effect of continuous light at low temperatures on growth in Atlantic salmon reared in commercial size sea pens

The aim of this study was to investigate the effect of continuous light of different duration, applied from late autumn to spring in the second year of the production cycle, on the production performance of Atlantic salmon in Northern Norway. The underlying hypothesis is that the introduction of continuous light (LL) superimposed on the natural light before December (the preferred continuous light regime in Northern Norway) could enhance growth and inhibit maturation in the subsequent year. To test this, two large, commercial scale experiments were performed [Experiment 1 in 2014 at 69.47°N, 18.26°E, and Experiment 2 in 2015 at 69.80°N, 19.42°E] where salmon of initial size of 1–1.5kg were subjected to LL at different time points during the period between 11 November and 13 December, and reared under LL until 31 March the following year. In Experiment 1 the water temperature at 6m depth ranged between 6.7°C in November and 3.6°C in March and in Experiment 2 the water temperature at 6m depth ranged between 8.3°C in November and 3.6°C in March and 6.8°C in May 2016. Before and after the period with LL, all fish were reared under natural light. Growth was improved by 13–20% in the early exposed groups (15 Nov and 11 Nov) compared to the late exposed groups (13 Dec.). No maturation was seen in the experimental groups at slaughter (Exp. 1: July–September 2015, Exp. 2: May 2016). Vertebra deformities did not differ between the early and late exposed groups suggesting that continuous light promotes growth at lower temperatures, while supporting normal vertebra development. Only minor differences in flesh texture (measured as differences in cathepsin L+B activity) were found in both experiments. It is concluded that a considerable growth benefit may be achieved by exposing Atlantic salmon to continuous light from early November in their first year in seawater, i.e. one month earlier than presently used by the salmon farming industry in Northern Norway.

Growth, development and behaviour of Persian sturgeon Acipenser persicus larvae in different light regimes

The effects of five different light regimes on growth performance and behaviour of Persian Sturgeon larvae were examined. Larvae were reared under five different photoperiods (24L, 12L:12D, 16L:8D, 8L:16L and 24D), from hatching (25.8 ± 8.1 mg; 12 ± 0.6 mm) to 28 days post-hatch (dph). Except the last week, there was no significant difference in growth parameters among the experimental groups. Growth performance significantly improved in larvae reared under a continuous light regime. The highest final length (34.5 ± 1.7 mm) was measured in 24L and the lowest one (29.5 ± 0.4 mm) in the constant darkness. Relative to other experimental groups, the continuous darkness had a retarding impact on the yolk sac absorption and swarming behaviour. Among the whole body compositions, the lowest body moisture content was measured in the continuous light group. Persian Sturgeon pre-larvae and larvae were not completely dependent on light regimes (in 1–21 days), whereas on the basis of measured parameters (total length, wet and dry weight and digestive fullness index) a continuous light regime played a decisive role on growth performance beyond 21 dph.

The effects of light, darkness and intermittent feeding on the growth and survival of reared Atlantic bonito and Atlantic bluefin tuna larvae

In larval culture, long light photoperiod regimes are used to maximize ingestion rates by increasing the accessibility to prey and therefore enhancing larval growth. Intermittent feeding could provide a viable alternative to the commonly used continuous feeding regimes that aim to improve larval growth and survival. In this study, we investigate the effect of alternating light/darkness regimes with intermittent feeding on the growth and survival of piscivorous larvae of two Scombrid species: Atlantic bonito, Sarda sarda (Bloch, 1793) and Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758). First we tested if the manipulation of a light regime generated intermittent feeding by analyzing the larval stomach content. Then, we conducted two laboratory experiments to identify the best alternating light regime that maximized larval growth and survival by comparing the results to those obtained using continuous light regimes. The manipulation of light was optimized to provide intermittent feeding opportunities for the larvae, since we discovered a clear interruption of feeding in darkness. An increase in specific ingestion throughout the day was observed in all experiments, reaching a maximum peak late in the day. Bluefin tuna larval growth rates were similar despite different alternating conditions whereas the bonito larvae grew best when provided with light at three hour intervals. In both species, growth under alternating light conditions was similar to the 15 hours continuous light treatment. No differences between the alternating and the continuous light treatments were observed in terms of their survival. Our results suggest that alternating light/feeding periods may have a beneficial effect on ingestion rates; possibly because feeding is less satiation-limited, metabolic costs are lower; or food digestion is more efficient under these conditions. Changes in the light regime, that result in pulse feeding, can thus be an optimal strategy to increase growth at no apparent survival cost in bonito or bluefin tuna larval cultures.

The effect of low temperatures and photoperiods on growth and vertebra morphometry in Atlantic salmon

The aim of this study was to reveal possible interactive effects of temperature and photoperiod on somatic and skeletal growth, feed conversion, organ indexes and blood chemistry in Atlantic salmon postsmolts. A total of 1140 (initial mean weight 96.0 g ± 3.1 SEM) juvenile Atlantic salmon reared in seawater were in duplicates exposed to six different combinations of temperatures (4.3, 6.5 or 9.3 °C) and photoperiods (continuous light, LL or simulated natural photoperiod (69oN), LDN) for 124 days. An interactive effect of photoperiod and temperature on somatic growth was found as the fish exposed to low temperature and continuous light regime (4LL) had a significantly higher growth (30 % gain in overall SGR) than the 4LDN group, corresponding to the effect of approx. 1.2 °C temperature increase. Fish in the 6 and 9 °C groups did not show any significant growth benefit of continuous light. Compared to the 4LDN group, the 4LL group showed higher total feed conversion efficiency, lower levels of blood Na+ and lower hepato-somatic and cardio-somatic indexes. In the skeleton, cervical vertebra were largest in the 4LL group, while the length of the head was largest in the 4LDN group, continuous light promotes growth at lower temperatures while supporting a normal development. It is suggested that a considerable growth benefit may be achieved by exposing juvenile Atlantic salmon to continuous light when reared at low (in this trial 4.3 °C) water temperature during winter.

Effects of starvation, subsequent feeding and photoperiod on flesh quality in farmed cod (Gadus morhua)

The study was designed to investigate the effect of four cycles of 5 weeks starvation followed by 10-week refeeding compared with daily feeding under either natural photoperiod or continuous light (LL) regime on body composition and flesh quality in Atlantic cod in sea cages, northern Norway. The fish were sampled for body composition and flesh quality parameters at the start of the trial, twice at the end of a 10-week feeding period and twice at the end of a 5-week starvation period. There was effect of both feeding and light regime on growth, the two starving groups losing weight during starvation and regaining weight during refeeding, and the group under LL being heavier. But, the mean overall growth did not vary between groups. Starvation/refeeding regime resulted in higher slaughter yield, but no overall effect was seen on hepatosomatic index, water content, water holding capacity (WHC), muscle pH, hardness or flesh colour compared with control groups. Continuous light increased gutted weight and slaughter yield, lowered WHC and depressed maturation compared with fish under natural light regime. Increased growth rate resulted in softer fillets and lower muscle pH.

Efeitos da temperatura e regime de luz sobre Corynespora cassiicola e da temperatura e período de molhamento foliar no desenvolvimento da mancha-alvo em acerola

RESUMO O presente estudo teve como objetivos: (i) determinar, in vitro, o efeito da temperatura sobre o crescimento micelial (10 a 35oC) e a germinação de conídios (10 a 45oC) de Corynespora cassiicola ; (ii) avaliar, in vitro , o efeito do regime de luz (luz contínua, fotoperíodo de 12 h e escuro) sobre o crescimento micelial, a esporulação e a viabilidade dos esporos de C. cassiicola ; e (iii) verificar, in vivo , a influência da temperatura (20 a 30oC) e da duração do período de molhamento foliar (4 a 48 h) no desenvolvimento da mancha-alvo em folhas de acerola. As temperaturas ótimas, estimadas a partir das equações, para o crescimento micelial e a germinação de esporos foram de 30 e 29oC, respectivamente. O regime de luz não afetou o crescimento micelial e a germinação dos esporos, entretanto, luz contínua favoreceu a esporulação, e a ausência de luz durante a produção dos esporos diminuiu sua viabilidade. Houve um incremento na área das lesões da mancha-alvo em folhas de acerola conforme a temperatura aumentou até 30oC. Foram necessárias 12 h de molhamento foliar para que a infecção e as lesões ocorressem.

Effect of photoperiod manipulation on the growth performance of juvenile lenok, Brachymystax lenok (Pallas, 1773)

Summary The effect of four different light regimes on growth was studied in lenok, Brachymystax lenok. Fish with average weights of 5.5 g were subjected to four different photoperiods (0L:24D, 6L:18D, 12L:12D and 24L:0D) for 35 days. The specific growth rate (SGR) of lenok in 24-h darkness had a significantly higher SGR than those in the continuous light regime (P < 0.05); however, there was no significant difference among fish exposed to 6L:18D, 12L:12D and 24L:0D photoperiods. There was a tendency for higher food intake over the light period extension from 0L to 24L, and feed intake was significantly higher in the continuous light group than in 24-h darkness (P < 0.05). No significant difference in feed conversion efficiency (FCE) was observed between fish exposed to 0L:24D and 6L:18D photoperiods, however, the FCE in both photoperiods was significantly higher than that in the other two groups. The final survival rate of juveniles varied from 79.67 to 95.33%, with significant differences among experimental groups. Fish tested in continuous illumination spent much more energy on respiration and excretion while depositing less energy for growth than in the other photoperiods. In contrast, fish in 24-h darkness deposited more energy for growth and spent less energy on respiration and excretion. Results show that photoperiod manipulation can affect growth, and that a continuous dark regime could improve growth in lenok at this stage of development.

Effect of circadian cycle and prey density on the demography of the predator Asplanchna silvestrii (Rotifera)

We studied the demographic responses (average lifespan (ALS), gross reproductive rate (GRR), net reproductive rate (NRR), generation time (GT) and the rate of population increase per day (r) of the predatory rotifer A. silvestrii cultured under five different durations of light conditions (L:D = 24:0, 18:6, 12:12, 6:18, and 0:24 in a 24 h cycle) and under two prey (Plationus patulus) densities (0.5 and 5.0 ind. mL−1). Our data showed that regardless of prey density, the survivorship of A. silvestrii was affected by the duration of photoperiod; the longest ALS was under complete darkness. For any given prey density, lowest GRR was recorded at 24L:0D. The NRR was lower under continuous light (24L:0D) regime. The longest GT was recorded when Asplanchna silvestrii was fed on high prey density and under total dark regime. The r ranged from 0.15 (24L:0D photoperiod in low prey density) to 0.6 day−1 (18L:6D and high prey density) and for the rest of treatments, the values remained within this range.

Comparison of the growth performance of offspring from cultured versus wild populations of arctic charr,Salvelinus alpinus(L.), kept at three different temperatures

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

Identification of a photolabile period for reducing sexual maturation in juvenile male sea bass (Dicentrarchus labrax) by means of a continuous light regime

The objective of this study was to identify a photolabile period suitable for reducing precocious gonadal maturation in juvenile male sea bass (Dicentrarchus labrax) through the exploration of discrete windows of continuous light (LL), 1–2 months in duration, in late summer-early autumn. Somatic growth, 11-ketotestosterone plasma levels, and the rates of testicular maturation and spermiation were analyzed to evaluate the effect of the applied photoperiodic regimes. Three LL treatments, with duration of 2 months each, were previously screened between the months of August and November. Administration of LL during the October–November period failed to show any differential effects in reducing early maturation, as compared to the simulated natural photoperiod. However, the August–September period was considered to be a likely candidate for photolability. To define this photolabile period, four LL treatments with duration of 1 month were then screened within the same late summer period. Our results demonstrate that the time interval including the month of September is the most sensitive photolabile period in order to reduce precocious gametogenesis in sea bass.