Short Light Periods Research Articles

Impact of light and nutrient availability on the phagotrophic activity of harmful bloom-forming dinoflagellates

Abstract Phagotrophy is a key nutritional mode for many bloom-forming dinoflagellates that can supplement their carbon and nutrient requirements. However, the environmental drivers and ecological relevance of phagotrophy in algal blooms are still poorly understood. This study evaluates the effect of light and nutrient availability on the phagotrophic activity of three common bloom-forming dinoflagellates (Alexandrium minutum, Heterocapsa triquetra and Prorocentrum micans) using three fluorescently labeled preys: bacteria, Synechococcus and the haptophyte Isochrysis galbana. The three dinoflagellates exhibited distinct responses to light and nutrient availability in terms of growth, cell size, prey ingestion and preference. A. minutum and H. triquetra showed higher cell-specific ingestion rates on bacteria (0.53 ± 0.13 and 1.64 ± 0.39 prey dinoflagellate−1 h−1, respectively) under co-limited nutrient and light availability, whereas P. micans showed higher ingestion on Synechococcus (0.93 ± 0.22 prey dinoflagellate−1 h−1) under low-light availability alone. However, the three dinoflagellates exhibited the highest carbon and nitrogen-specific ingestion rates when feeding on the larger prey I. galbana. Our findings indicate that phagotrophy could be of advantage in short periods of light or nutrient limitation and may play different roles during the development of blooms, likely influencing the energy transfer through the food web.

Effects of photoperiod on the growth and physiological responses in Ulva prolifera under constant and diurnal temperature difference conditions

Photoperiod and temperature are two main factors in the growth of macroalgae, and changes in photoperiod and diurnal temperature difference exist in natural condition. In order to study the effects of photoperiod and diurnal temperature difference on the growth of green algae Ulva prolifera, we cultured this species under three light/dark cycles (light: dark = 10:14, 12:12 and 16:08) with constant (22 °C for light and dark period, noted as 22-22 °C) and diurnal temperature difference (22 °C and 16 °C for light and dark period, respectively, noted as 22-16 °C) conditions. The results showed that: 1) Compared with 10:14 light/dark cycle, the growth of U. prolifera under 12:12 light/dark cycle was significantly enhanced by 39% and 16% for 22-22 °C and 22-16 °C treatments, respectively, while the increase proportion decreased when the daylength increase from 12 h to 16 h. 2) The enhancement in growth induced by diurnal temperature difference was observed under 10:14 light/dark cycle, but not for 12:12 and 16:08 light/dark cycle treatments. 3) The Chl a content and photosynthetic rate increased under short light period and 22-22 °C conditions, while under 22-16 °C conditions, higher photosynthetic rate was observed under 12:12 light/dark cycle and no significant difference in Chl a content was observed. 4) Under 22-22 °C conditions, compared with 10:14 (L:D) treatment, the expression levels of proteins in light-harvesting complexes, PSII and carbon fixation were down regulated, while the photorespiration and pentose phosphate pathway (PPP) were up regulated by 16:08 light dark cycle. Then we speculate that the higher photosynthetic rate may be one compensation mechanism in short photoperiod, and under long light period condition the up regulations of photorespiration and PPP can be in charge of the decrease in enhancement growth induced by longer daylength.

Aqueous Suspension of Porous SiO<sub>2</sub> Nanoparticles, Containing 9,10-diphenylanthracene, in Agrophotonics

An aqueous colloidal suspension of porous silicon dioxide nanoparticles containing an organic phosphor 9,10-diphenylanthracene was obtained by ultrasonic dispersion. The average size of suspension nanoparticles is 15–25 nm. This suspension has a characteristic absorption spectrum for diphenylanthracene in the region from 345 to 420 nm and a photoluminescence spectrum in the region from 400 to 550 nm. The resulting suspension was used for irrigation when growing bulbous plants (lilies and gladiolus) under conditions of a short light period with additional lighting with LEDs-based phytolamps with red and blue spectra. It has been established that the use of this suspension with nanoparticles that enter plants as an artificial photosynthetic pigment accelerates the growth of bulbous plants by an average of 15–20% compared to control samples under the same lighting conditions.

Minimising the energy footprint of indoor food production while maintaining a high growth rate: Introducing disruptive cultivation protocols

The majority of the cultivated species in indoor vertical farms require many hours of light each day to reach their full potential in terms of biomass, leaf size, nutritional value, taste, and colour. At the same time, the cost of electricity can be very high due to the many hours of operation, which can be an inhibiting factor for the advancement of technology and the profitability of the farm. In this study, we tested the growth of basil plants ( Ocimum basilicum ) under continuous and intermittent photoperiods. The leaf physiological traits of three different photoperiod treatments were assessed and used to estimate the toleration rate of the plants under different light schedules. In the first indoor growth chamber, the plants were grown under 16 h of continuous light, in the second chamber under a normal photoperiod of 14 h with intermittent light, and in the third chamber under a load-shifting demand response with 14 h of intermittent light. The purpose was to evaluate and design flexible intermittent light exposure to reduce the electricity consumption for crops grown in indoor environments while maintaining a high growth rate and biomass production of the plants. The presented results of this experimental research show a positive correlation of the plants’ responses to abiotic stress when exposed to short 10-min periods of intermittent light, without having significant effects on the physiological responses of the cultivation. The physiological, biochemical, and morphological status of the plants were assessed in terms of photosynthetic rate, chlorophyll pigments, stomatal conductance, and transpiration rate of the plants. The protocol with intermittent light exposure induced a significantly 47% increase in biomass production compared to the continuous photoperiod, resulting in a more economical, sustainable, business, and ecological impact on the energy footprint of indoor food production. • Positive plants' response to abiotic stress when exposed to intermittent light. • Intermittent light induced a significant 47% increase in biomass production. • Vertical farms can be more profitable where dynamic electricity prices are offered.

Impact of lighting regimes on reproductive performance and sperm ultrastructure in rabbit bucks under very severe heat stress conditions

Lighting regimen is an important part of animal reproductive performance and physiological parameters, which can minimize the effect of high ambient temperature on semen quality and fertility of animals. The potential application of different light regimes in improving blood biochemicals, antioxidants capacity, reproductive hormones, semen quality, sperm ultrastructure alterations and fertility of rabbit bucks exposed to high ambient temperature was evaluated. Fifty bucks were allocated into five groups (10/group) according the lighting regimes. Bucks in each group were exposed to one of the following daily light-dark cycle (16L: 8D, 14L: 10D, 12D:12L, 10L: 14D or 8L: 16D) for four months (June to September). The ambient temperature, relative humidity and temperature–humidity index values during the experimental period were 34.25 ± 0.18°C, 63.68 ± 0.75%, 32.01 ± 0.33, respectively, indicating that the experimental bucks were under very severe heat stress conditions. Bucks exposed to 10L: 14D and 8L: 16D light regimes had significantly lower (P < 0.05) feed intake, rectal temperature, respiration rate, aspartate and alanine aminotransferases activities, and malondialdehyde level compared with their counterparts. Melatonin, testosterone, FSH, LH, and total antioxidants capacity levels were significantly increased (P < 0.05) by decreasing photoperiod, being the maximum for 8L: 16D regime. Bucks exposed to 10L: 14D and 8L: 16D light regimes exhibited significant improvement in sexual desire, semen quality (including: ejaculate volume, sperm progressive motility, vitality, intact acrosome and membrane integrity, sperm concentration and total sperm output) and fertility.The results indicate that application of short light period (8L: 16D) can be used as alternative and beneficial strategy to rabbit producers during heat stress months for improving semen quality, antioxidative capacity and fertility of bucks.

The zeaxanthin epoxidase is degraded along with the D1 protein during photoinhibition of photosystem II.

The xanthophyll zeaxanthin is synthesized in chloroplasts upon high light exposure of plants and serves central photoprotective functions. The reconversion of zeaxanthin to violaxanthin is catalyzed by the zeaxanthin epoxidase (ZEP). ZEP shows highest activity after short and moderate high light periods, but becomes gradually down‐regulated in response to increasing high light stress along with down‐regulation of photosystem II (PSII) activity. ZEP activity and ZEP protein levels were studied in response to high light stress in four plant species: Arabidopsis thaliana, Pisum sativum, Nicotiana benthamiana and Spinacia oleracea. In all species, ZEP protein was degraded during photoinhibition of PSII in parallel with the D1 protein of PSII. In the presence of streptomycin, an inhibitor of chloroplast protein synthesis, photoinhibition of PSII and ZEP activity as well as degradation of D1 and ZEP protein was strongly increased, indicating a close correlation of ZEP regulation with PSII photoinhibition and repair. The concomitant high light‐induced inactivation/degradation of ZEP and D1 prevents the reconversion of zeaxanthin during photoinhibition and repair of PSII. This regulation of ZEP activity supports a coordinated degradation of D1 and ZEP during photoinhibition/repair of PSII and an essential photoprotective function of zeaxanthin during the PSII repair cycle.

Future CO2-induced seawater acidification mediates the physiological performance of a green alga Ulva linza in different photoperiods.

Photoperiods have an important impact on macroalgae living in the intertidal zone. Ocean acidification also influences the physiology of macroalgae. However, little is known about the interaction between ocean acidification and photoperiod on macroalgae. In this study, a green alga Ulva linza was cultured under three different photoperiods (L: D = 8:16, 12:12, 16:8) and two different CO2 levels (LC, 400 ppm; HC, 1,000 ppm) to investigate their responses. The results showed that relative growth rate of U. linza increased with extended light periods under LC but decreased at HC when exposed to the longest light period of 16 h compared to 12 h. Higher CO2 levels enhanced the relative growth rate at a L: D of 8:16, had no effect at 12:12 but reduced RGR at 16:8. At LC, the L: D of 16:8 significantly stimulated maximum quantum yield (Yield). Higher CO2 levels enhanced Yield at L: D of 12:12 and 8:16, had negative effect at 16:8. Non-photochemical quenching (NPQ) increased with increasing light period. High CO2 levels did not affect respiration rate during shorter light periods but enhanced it at a light period of 16 h. Longer light periods had negative effects on Chl a and Chl b content, and high CO2 level also inhibited the synthesis of these pigments. Our data demonstrate the interactive effects of CO2 and photoperiod on the physiological characteristics of the green tide macroalga Ulva linza and indicate that future ocean acidification may hinder the stimulatory effect of long light periods on growth of Ulva species.

Variability of photosensitive period and voltinism among populations of a butterfly, Ypthima multistriata, inhabiting similar latitudes and altitudes

AbstractIn Ypthima multistriata Butler (Lepidoptera: Nymphalidae), there are univoltine and bivoltine populations in adjacent areas with similar climatic conditions. A previous study revealed that larvae of both univoltine and bivoltine populations diapause under a constant short day (i.e., a constant short light period; L13:D11), but not under a constant long‐day condition (L16:D8). However, in both types of populations, adults of an overwintering generation appear and oviposit in June and soon thereafter larvae hatch. Therefore, the younger larvae (at least the first instars) of both types of populations experience a long day; nevertheless, the larvae of univoltine populations diapause in nature. To resolve this inconsistency, we set up two hypotheses: (1) the photosensitive stage of larvae is the second instar or later, and (2) the photosensitive stage of univoltine populations is later than that of bivoltine populations. To test these hypotheses, we performed rearing experiments with two univoltine populations and two bivoltine ones. The results indicated that the photosensitive stage was the second or third instar and that the photosensitive stage was later in one univoltine population than in the two bivoltine populations. Larvae of the other univoltine population diapaused under all conditions. The former result supports our hypothesis, and the latter result indicates that the response to photoperiod is different among univoltine populations. In addition, larval development was slower in one univoltine population than in the bivoltine populations, which also delays the timing of the diapause decision in this univoltine population. Larvae that experienced a long day during the first and middle instars but experienced a short day at the end of their larval stage developed faster than larvae that experienced a constant long day. This may be an adaptation to enable emergence before the start of a cold season that is unsuitable for reproduction.

Control of seasonal reproduction in sheep and goats by light and hormones

Seasonal variations of reproductive ability have been demonstrated in male and female sheep and goats. For the female, there is a distinct breeding season. Whilst there are large breed differences in the duration of the sexual season, oestrous cycles generally start when daylength is decreasing and end when daylength is increasing. In some breeds, ovulation without oestrus occurs during the non-breeding season. Although males are able to mate all the year round, seasonal variations occur in the weight of the testis and seminal vesicles and in the fructose concentration of the seminal vesicles. Sexual behaviour and semen characteristics also show seasonal variations. These seasonal variations in males and females are related to hormonal levels. FSH and LH concentrations in the pituitary are reduced to 50% during the non-breeding season. In the peripheral blood, LH concentrations vary throughout the year whilst prolactin concentrations follow the pattern of daylength. Steroid hormones and their feedback actions at the hypothalamo-pituitary axis play a role in the regulation of seasonal reproduction. Three different ways are proposed to overcome these seasonal variations. (1) Males can be introduced into a flock of females before the onset of the breeding season. This leads to induction of ovulation and oestrus, although the first ovulation is frequently followed by a short luteal phase. Teasing does not necessitate contact or sight and is only effective after a period of isolation of the females from the males. (2) Oestrus and ovulation may be induced during the anoestrous period by hormonal treatments. Inducers of LH release have to be associated with a progestagen treatment; PMSG is still the most efficient inducer of LH release. Artificial insemination is useful in this context to avoid subfertility due to seasonal variations of the male. (3) The period of reproduction may be controlled by artificial light regimens. There is a photoinducible period in the circadian cycle of the ewe and it may soon be practical to breed out of season by timed exposure of ewes to short periods of light during the normal hours of darkness.

The effect of constant darkness and short light periods on the survival and physiological fitness of two phytoplankton species and their growth potential after re-illumination

We tested the survival potential and fitness of two different algae strains (the diatom Thalassiosira weissflogii and the cryptophyceae Rhodomonas sp.) under different growth conditions (complete darkness and short light intervals, simulating conditions in a deep mixed water column) at different temperatures, plus the effect of these conditions on the physiological fitness and growth after re-illumination was examined. Both species survived the experimental conditions without significant cell loss or physiological damage. Two different survival strategies were observed: (1) the diatom T. weissflogii immediately reduced its metabolic rate and stopped cell division. The effect on chlorophyll a (chl-a) content and photosynthetic capacity was negligible. At 10 °C, T. weissflogii used the short light windows to metabolize carbohydrates and growth. (2) The cryptophyte Rhodomonas sp. initially continued to grow after transfer into all trials. However, the cell number decreased after day 6. Carbohydrate and chl-a content went on to decrease dramatically (70 and 50%, respectively). After 3 days of re-illumination, T. weissflogii grew faster than of Rhodomonas sp.. The diatom seemed to benefit from better start conditions and would out-compete the cryptophyte during a spring bloom. Our results highlight that these algae groups have different strategies in dealing with darkness, which potentially endow diatoms with a competitive advantage in deep mixed waters and in the season of early spring.

Environmental conditions for Diaphorina citri Kuwayama (Hemiptera: Liviidae) take‐off

AbstractEnvironmental factors that influence flight activity of Diaphorina citri Kuwayama (Hemiptera: Liviidae) may have implications for Huanglongbing spread and management. In this work, four studies were conducted to evaluate the effect of environmental conditions on D. citri take‐off. In the first, insects were transferred to sweet orange seedlings and confined inside an acrylic cage to verify the take‐off periodicity and the effect of environmental factors on this process. In the second, take‐off temperature threshold was estimated by recording the number of insects that initiated flight from a platform when subjected to gradual temperature increases from 15 to 39°C. In the other studies, we evaluated the effect of different photoperiods and temperature regimes (third study) and of constant temperatures (fourth study) on the propensity for D. citri flight. Insects were confined in clear plastic bottle cages with tubes of 50 ml placed on the cab, to collect emerged adults that initiated flights. Results showed that a small portion of the tested population (maximum 10%) tends to take off from plants and this behaviour is more prevalent in the afternoon (14:00–16:00 h), coinciding with daytimes of lower humidity and higher thermal amplitude. Adults that were submitted to lower temperatures (18°C) and short light periods (10 h) showed less propensity to flight. In contrast, at constant 27°C, the insects were more prone to flight, and this result was confirmed when individuals were submitted to increases in temperature, indicating that 27.14°C is the take‐off temperature threshold of D. citri. Results show that temperature plays an important role in the flight activity of D. citri and suggest that control measures of the insect may be more effective in the morning and in temperatures below 27°C, when the probability to take off from a host is lower.

Characterizing short-term light dynamics in forested headwater streams

Light controls local- and reach-scale primary production in forested headwater streams. In terrestrial ecosystems, short periods of elevated light beneath canopies (sunflecks) are instrumental in maintaining understory autotrophic production, but sunflecks are unexplored and uncharacterized in stream systems. We described short-term light dynamics in 4 forested headwater streams in the western Cascade Mountains of Oregon. We quantified the prevalence and characteristics of sunflecks, compared the timing of light exposure at stream sites to a sensor in full sun, and evaluated whether sunfleck characteristics differed between stream sections in old-growth vs second-growth forest. Sunflecks were common in streams. A minimum of 3 individual sunflecks/d occurred at each of 47 sensor locations. Short sunflecks were more common than long sunflecks, a result consistent with findings in terrestrial studies. However, streams had longer sunflecks than upland forests in this region, probably because canopy gaps are larger over stream channels than in the forest. In >½ of the 47 sensor locations, daily light distributions differed between in-stream and full-sun locations, revealing that canopies affect both the total light and the timing of light delivery to understory locations. The timing of peak stream temperature coincided better with light delivery by sunflecks than in full sun. Peak stream temperature was offset by ≥3 h from midday peak light in full sun, but beneath the forest canopy at the 4 surveyed streams, 26 to 60% of sunfleck events occurred within 2 h of peak stream temperature. These findings highlight the presence and potential importance to in-stream autotrophy of short-term light events (sunflecks) in forested streams. In a model simulation, a 1-h sunfleck increased stream primary production 5 to 17%, depending on the time of day that sunfleck occurred.

A PERIOD3 variant causes a circadian phenotype and is associated with a seasonal mood trait

In humans, the connection between sleep and mood has long been recognized, although direct molecular evidence is lacking. We identified two rare variants in the circadian clock gene PERIOD3 (PER3-P415A/H417R) in humans with familial advanced sleep phase accompanied by higher Beck Depression Inventory and seasonality scores. hPER3-P415A/H417R transgenic mice showed an altered circadian period under constant light and exhibited phase shifts of the sleep-wake cycle in a short light period (photoperiod) paradigm. Molecular characterization revealed that the rare variants destabilized PER3 and failed to stabilize PERIOD1/2 proteins, which play critical roles in circadian timing. Although hPER3-P415A/H417R-Tg mice showed a mild depression-like phenotype, Per3 knockout mice demonstrated consistent depression-like behavior, particularly when studied under a short photoperiod, supporting a possible role for PER3 in mood regulation. These findings suggest that PER3 may be a nexus for sleep and mood regulation while fine-tuning these processes to adapt to seasonal changes.

Humpback whale songs during winter in subarctic waters

The songs of the male humpback whales (Megaptera novaeangliae) have traditionally been associated with mating at tropical and subtropical mating grounds during winter. However, songs also occur out of mating season, both on feeding grounds in spring, late summer and fall. This study provides the first report of humpback whale singing behaviour in the subarctic waters of Northeast Iceland (Skjalfandi Bay) using long-term bottom-moored acoustic recorders during September 2008–February 2009 and from April to September 2009. Singing started in late November and peaked in February, within the breeding season. No songs were detected from spring to fall, despite visual detections of humpback whales. Non-song sound signals from humpback whales were detected during all recording months. Songs were partly composed of fundamental units common with other known mating grounds, and partly of song units likely unique to the study area. The variety of song unit types in the songs increased at the end of the winter recordings, indicating a gradual change in the songs throughout the winter season; as has been shown on traditional mating grounds. The relative proportion of songs compared with non-song signals was higher during dark hours than daylight hours. The short light periods of the winter, and where food is available, likely influence the daily occurrence of humpback whales’ songs in the subarctic.

Foraging behavior of Scaptotrigona depilis (Hymenoptera, Apidae, Meliponini) and its relationship with temporal and abiotic factors

Stingless bees play an important role in Tropical and Subtropical ecosystems as pollinators of many plants. The aim of this study was to characterize the pattern of flight activity and foraging for pollen by Scaptotrigona depilis workers and their relation with climatic and temporal factors. We observed flight activity from July 2001 to June 2002 and pollen collection by scoring the flow of workers entering and exiting the colonies. We tested whether environmental (temperature, relative humidity, pluviosity and luminosity) and temporal predictors (month and time of day) affected bees’ activities. The study was conducted during one year and the records of observations showed that during the dry season when the length of light is longer, the external activity was more intensive, while during cold months with shorter light period, foraging activity was reduced. Pollen collection showed a peak in February, but in general this activity was regulated by temperature, humidity and daily luminosity.

Transcriptional profile of differentially expressed genes related to abortive flower buds under short light period stress in petunia

The long-day plant Petunia×hybrida ‘Fantasy Red’ was found to produce a considerable number of premature abortive flower buds when placed under short light period stress. Suppression subtractive hybridization (SSH) was performed to compare the gene expression profiles between normal and abortive petunia flower buds as induced by short light periods. Using reverse northern blotting, a total of 912 positive clones were successfully identified and sequenced, and 289 non-redundant, differentially expressed transcripts were obtained. According to the Blast2GO and KEGG pathway analyses, the significant distinct cellular component was identified as mitochondrion, and the notable different metabolic pathways were ascribed to carbohydrate metabolism and lipid metabolism. The quality of the SSH libraries was verified through quantitative real-time reverse transcription-PCR (qRT-PCR) analysis of 14 genes. In addition, six of these genes were demonstrated to be of temporal and/or spatial specificity using qRT-PCR, implying that they might be responsible for the premature flower abortion. Furthermore, Phms2 (KC465381), a sequence sharing a high degree of similarity with male sterility 2 gene was characterized, and its inconsistent expression pattern predicted a novel role for Phms2 in flower bud abortion. The data presented here provide insight into the molecular mechanisms of premature flower abortion under short light periods and, hence, may be of value for assessing candidate genes with potential for creating novel germplasms with enhanced photoperiod stress tolerance.

Maternal effects of photoperiods on glycogen metabolism related to induction of diapause in Cotesia vestalis (Hymenoptera: Braconidae) from Jilin, China

Most insects must accumulate glycogen before entering diapause. Photoperiod influences diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). In this study, we measured glycogen content and the activity and messenger RNA (mRNA) expression of glycogen synthase and glycogen phosphorylase at different G0 (25 °C under light:dark photoperiods of 8L:16D, 12L:12D, and 16L:8D) and G1 life stages (13 °C under 8L:16D). Glycogen content in G0 and G1 increased with shorter light periods, except for G0 adult males, which showed no significant difference under the three photoperiods. Compared with those under 16 h, in those under 8 h light, glycogen synthase activity was significantly higher at all tested stages, except for G0 pupa and adult male, for which it was identical; mRNA expression was higher at G0 larva and prepupa, lower at pupa, and identical at rest stages. Glycogen phosphorylase activity was significantly higher for G1 egg, lower at G1 prepupa, and identical at all other stages; mRNA expression was higher at G0 and G1 larval stages, and similar at rest stages. These findings suggest that glycogen, being regulated by the two enzymes, may be a consequential factor in the transmission of maternal information and diapause induction of C. vestalis.

Twenty-four hours light exposure experiences in postpartum women and their 2–10-week-old infants: An intensive within-subject design pilot study

Background Adequate light exposure is critical for entraining circadian rhythms, regulating sleep–wake cycles, and maintaining optimal mood. Yet, few studies have reported normative data on light exposure experiences in postpartum women and young infants; none has examined the two simultaneously. Objectives The objective of this pilot study was to document the 24-h light exposure experiences in postpartum women and their infants. Design An intensive within-subject design was employed. Settings The participant’s natural home environment. Participants Twenty-four healthy mother–infant pairs were recruited from the general community in Seattle, USA. Two mother–infant pairs did not have complete data, resulting in a final sample size of 22 (12 female infants). Methods Mothers and infants wore a monitor to continuously record illumination levels for 7 days. Data were aggregated within subject to calculate summary measures of illumination exposure. Circadian patterns of light were examined using cosinor analysis. Pearson correlation was used to examine the relation between maternal and infant light exposure. Results Mothers spent 71.13 ± 11.58% and infants spent 80.07 ± 8.27% of their daytime hours (defined as 06:00–21:59) in an illumination level <50 lux. Mean minutes >1000 lux per day was 54 ± 39 for mothers and 23 ± 18 for infants. Maternal and infant light exposure exhibited a modest circadian pattern and a strong correlation, both in the timing of peak illumination exposure ( r = 0.93, p < 0.01) and in the level of light exposure ( r = 0.70 ± 0.07). Conclusions Postpartum women and infants experience low ambient light levels with short periods of bright light during the day. Whether this level of light is sufficient for optimal postpartum mood and infant circadian entrainment warrants further investigation. If higher levels of light were indeed necessary for postpartum women and young infants, increasing ambient light levels through the use of natural sunlight (i.e., walking outdoors) could be a simple and economic nursing intervention. The strong pattern synchrony between maternal and infant light exposure suggests that mothers play the primary role in providing a lighting environment suitable for infants to synchronize their circadian rhythms to a 24-h day.

Photoperiod affects growth, behaviour and stress variables in Clarias gariepinus

Short periods of light or no light (18D : 06L and 24D : 00L) resulted in an increased growth compared to extended periods of light (06D : 18L and 12D : 12L) in African catfish Clarias gariepinus. Fish under longer periods of light (12D : 12L and 18D : 06L) showed higher swimming activity, more aggression (injuries on the body) and higher lactate, free fatty acids and cortisol levels compared to those who were reared at shorter periods of light (24D : 00L and 18D : 06L). Feeding activity during light and dark periods in this experiment showed that C. gariepinus had both night and day feeding activities, with a preference to diurnal feeding in the 12D : 12L photoperiod. The results showed that light plays an important role in the African catfish behaviour and its well‐being. As the hours of light increased during the 24 h cycle, data suggests that the fish were more stressed and aggressive, compared to those under a reduced number of light hours.

FATTY ACIDS, STEROLS AND α‐TOCOPHEROL IN ISOCHRYSIS GALBANA

ABSTRACT The production of fatty acids, sterols and α‐tocopherol by Isochrysis galbana under 24 h and 8 h lighting was studied. The most abundant fatty acids were 14:0, 16:0, 16:1, 18:4ω3, 20:5ω3 and 22:6ω3. Higher accumulation of monounsaturated fatty acids was observed in the decay phase whereas in the lag phase polyunsaturated fatty acids (PUFA) were the major group. The shorter light period seemed to increase the production of PUFA. Sitosterol and stigmasterol were the two main sterols detected achieving the levels 246.3 and 220.0 mg/100 g, respectively. A continuous increase in the level of total sterols was recorded during the life cycle at 24 h lighting. The reduction of the photoperiod led to a decrease in the total sterols produced in the decay phase. An increase in α‐tocopherol production during the life cycle was recorded. The reduction of the lighting period considerably decreased the biosynthesis of this antioxidant.