Artificial Photoperiod Research Articles

Circadian rhythm of motor activity of the Brazilian rock cavy (Kerodon rupestris) under artificial photoperiod

Kerodon rupestris, a Brazilian caviidae rodent, lives in dry stony places. In a first experiment, seven animals were kept in LD (250:0 lux and 400:0 lux) during 40 days in each condition. In the second, four animals were kept in LD (470 lux: red dim light) for 47 days, then in LL (470 lux) for 18 days and in DD (red dim light) for 23 days. Motor activity was continuously recorded by infrared sensors. Animals showed entrained rhythms to the LD cycle being light and dark active, with higher values in phase transitions. When the light intensity was increased, four animals increased and two reduced the activity. In LL, three animals expressed an endogenous tau of 24.4, 26.5 and 24.6 h and one was arrhythmic; in DD, two expressed tau of 23.6 and 23.7 h and one was arrhythmic. Results indicate that Kerodon rupestris circadian rhythm is affected by light intensity but it is not yet possible to determine its habit.

Parâmetros reprodutivos de bodes submetidos ao manejo de fotoperíodo artificial

Objetivou-se com este estudo avaliar parâmetros reprodutivos (comportamento sexual, perímetro escrotal e aspectos quantitativos e qualitativos do sêmen) de bodes (jovens e adultos) das raças Alpina e Saanen submetidos ao manejo de fotoperíodo artificial (16 horas de luz e 8 horas de escuro durante dois meses). Os animais jovens demonstraram maior libido que os adultos, considerando-se o menor tempo de reação. Houve variação na freqüência de manifestação das características comportamentais, tanto entre raças quanto entre idades, e, em todas essas características, foi verificada maior intensidade para os animais adultos. Bodes Alpinos apresentaram menor perímetro escrotal que os bodes Saanen na mesma idade. O perímetro escrotal aumentou de 30,53 cm no período 1 (primeiros 15 dias após o final do manejo com fotoperíodo artificial) para 31,53 cm no período 2 (restante do experimento). Bodes Alpinos produziram sêmen de melhor qualidade que os Saanen de mesmo grupo de idade. Bodes das raças Alpina e Saanen criados nas condições deste experimento são sensíveis (sensibilidade mais pronunciada em animais adultos). Quanto aos parâmetros reprodutivos avaliados, às variações sazonais ao longo do ano.

Effects of dietary astaxanthin supplementation on reproductive characteristics of rainbow trout (Oncorhynchus mykiss)

Summary The effect of dietary astaxanthin supplementation on reproductive characteristics was investigated in five groups of female rainbow trout broodstock fed diets containing either 0.07, 12.46, 33.33, 65.06 or 92.91 mg astaxanthin kg−1, respectively, and two groups of male rainbow trout broodstock fed diets supplemented with 0.07 and 33.33 mg astaxanthin kg−1, respectively, for 6 months in an artificial photoperiod system until sexual maturation. The eggs from each group of female broodstock were divided into two equal batches. One batch was fertilized with homogenized sperm of four males fed diets with 0.07 mg astaxanthin kg−1 and the other portion with sperm of four males fed diets with 33.3 mg astaxanthin kg−1. The females produced eggs with astaxanthin concentrations ranging from 2.03 to 29.79 mg kg−1. Dietary astaxanthin supplementation had positive effects on investigated reproductive traits. Significant differences in rate of fertilization, percentage of eyed and hatched eggs, and mortality of eyed eggs were found between treatments (P 0.05). A significant difference (P < 0.05) in fertilization rate was found for male groups fed 0.07 and 33.3 mg astaxanthin kg−1. The astaxanthin content in the eggs and fertilization rate, eyed-egg percentage and percentage hatch were significantly correlated (P < 0.05). It is concluded that dietary supplements of astaxanthin are required for optimum reproduction in rainbow trout.

Effects of constant light on haematological parameters of cultured rainbow trout (Oncorhynchus mykiss) in the Southern Hemisphere

The effects of artificial photoperiod regimes on reproductive patterns have been studied in several species, as have haematological parameters. However, information on how artificial photoperiods may affect blood components is scarce, especially under field conditions. We have assessed the effects of constant light [long day (LD) photoperiod: 24 h (light):0 h (dark)] on haematological parameters of cultured rainbow trout in Chile (Southern Hemisphere). In the initial stage (March up to June), two groups of fish were maintained under similar conditions and under the ambient (natural) photoperiod (NP). One group was then placed under the LD photoperiod regime for 2 months (June/July), following which it was returned to␣the NP (August–January); the control group remained under the NP throughout the experiment (March–January). All fish were assessed for haematological parameters and growth performance at various times during the experiment. During the initial stage, no differences were found between groups. However, at the end of the LD 24:0 period, the LD fish had increased haematocrit values and erythrocyte numbers and diminished mean corpuscular haemoglobin. After the LD fish had been returned to the NP, they developed secondary sexual characteristics and had a 40–44% decrease in the number of leukocytes.

Padrão de deslocamento do camarão marinho Litopenaeus vannamei (Boone) (Crustacea, Decapoda, Penaeidae) nas fases clara e escura ao longo de 24 horas

Litopenaeus vannamei (Boone, 1931) daily behavior pattern is still poorly understood. With the aim of optimizing the management of shrimp farms through the study of this animal behavior, experiments were performed with juvenile (7.57 ± 1.01), which were marked and kept in aquariums (30 l). To record activity, the aquariums were submitted to an artificial photoperiod (light and dark phases, 12h:12 h), with 16 shrimp (33 m2) monitored in each phase for 20 days, for 15-minute periods every hour. Food was provided at random times and a record kept of horizontal and vertical displacement (continuous focal), swimming and exploration behavior (instantaneous focal). The horizontal and vertical displacements of the shrimp were greater during the dark phase, with a predominance of the swimming behavior. Exploration of the substrate occurred in both phases, with a peak between five and seven hours after the lights were turned on.

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders ( n = 8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group2 ganders ( n = 8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11 h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August–March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Taxa de gestação em cabras Alpinas e Saanen tratadas com hCG no terceiro dia após o estro

Avaliou-se o efeito da aplicação da gonadotrofina coriônica humana (hCG) sobre a taxa e duração da gestação e sobre a concentração plasmática de progesterona (P4) em cabras lactantes das raças Alpina (83) e Saanen (60), na estação de acasalamento induzida pelo programa de fotoperíodo artificial. Os animais foram distribuídos em dois tratamentos após a cobrição; as cabras do tratamento 1 (T1 controle) receberam solução salina via intramuscular (1ml), e as do tratamento 2 (T2) receberam 250UI do hCG, no terceiro dia no pós-estro. As taxas de gestação, detectadas por exame ultra-sonográfico, realizado no 35º após a cobrição, para as cabras das raças Alpina e Saanen controle e tratadas, foram de 80,4; 70,3; 72,7; 81,5%, respectivamente, não diferindo entre os tratamentos e entre as raças (P&gt;0,05). A taxa média de gestação foi 77,2 e 75,0% para os animais controle e tratados, respectivamente. A duração da gestação não foi influenciada pelos tratamentos (P&gt;0,05). As amostras de sangue para análise da concentração plasmática de progesterona (P4) foram coletadas de cinco cabras Alpina por tratamento, no dia do estro (dia 0) e aos 3, 8, 15, 21, 42 e 60 dias após o estro. Não houve diferença na concentração plasmática média de P4 entre os tratamentos (P&gt;0,05), sendo de 5,84ng/ml para T1 e 5,76ng/ml para T2. Observou-se diferença em relação aos dias de coleta (P&lt;0,05). O hCG aplicado no terceiro dia pós-estro não alterou a taxa de gestação e nem a concentração de P4.

Effects of different long-day photoperiods on somatic growth and gonadal development in Nile tilapia ( Oreochromis niloticus L.)

Long-day photoperiods are considered as an effective managerial tool in manipulating somatic growth and reproduction in a number of fish species. Effects of three different artificial long-day photoperiods on somatic growth and gonadal development of Nile tilapia ( Oreochromis niloticus L.) were investigated in this study. Swim-up fry with a mean initial weight of 0.06 g were exposed to 24L:0D, 20L:4D and 18L:6D artificial photoperiods and ambient light regime (control) for 24 weeks at 27.0 ± 1 °C. The effect of photoperiodic manipulation was only detectable and statistically meaningful during fingerling stage. Long-day photoperiods resulted in significantly higher mean final weights and specific growth rates (SGR) than natural light regime. The highest mean final weight (24.94 ± 0.45 g) and SGR (3.46 ± 0.03% day − 1 ) were obtained under 24L:0D photoperiod. Mean female gonadosomatic index (GSI) and mean oocyte size were significantly lower in fish maintained under continuous light regime (24L:0D) than those of 20L:4D, 18L:6D treatments and control. The highest gonadosomatic indices were recorded in control female and males. Mean oocyte diameter in fish exposed to continuous light was measured as 1.05 ± 0.06 mm with the bulk of the oocytes (60.0%) in pre-vitellogenic stage (≤ 1.20 mm). On the contrary, oocyte size and size distribution of oocytes in 20L:4D, 18L:6D photoperiod groups and control were indicating a more advanced oocyte development stage, i.e. vitellogenic (1.2–1.8 mm) and post-vitellogenic stages (> 2.1–2.4 mm). Basically, results obtained support the idea that continuous artificial lighting may be influential on enhancing somatic growth and delaying gonadal development in Nile tilapia during fingerling stage.

Adaptive responses of wild mungbean (Vigna radiata ssp. sublobata) to photo-thermal environment. II. Growth, biomass, and seed yield

The leaf growth, dry matter production, and seed yield of 11 wild mungbean (Vigna radiata ssp. sublobata) accessions of diverse geographic origin were observed under natural and artificial photoperiod–temperature conditions, to determine the extent to which genotypic differences could be attributed to adaptive responses to photo-thermal environment. Environments included serial sowings in the field in SE Queensland, complemented by artificial photoperiod extension and controlled-environment growth rooms. Photo-thermal environment influenced leaf growth, total dry matter production (TDM), and seed yield directly, through effects of (mainly cool) temperature on growth, and indirectly, through effects on phenology. In terms of direct effects, leaf production, leaf expansion, and leaf area were all sensitive to temperature, with implied base temperatures higher than usually observed in cultivated mungbean (V. radiata ssp. radiata). Genotypic sensitivity to temperature varied systematically with accession provenance and appeared to be of adaptive significance. In terms of the indirect effects of photo-thermal environment, genotypic and environmental effects on TDM were positively related to changes in total growth duration, and harvest index was negatively related to the period from sowing to flowering, similar to cultivated mungbean. However, seed yield was positively related to the duration of reproductive growth, reflecting the indeterminate growth habit of the wild accessions. As a consequence, the wild accessions are more responsive to favourable environments than typically observed in cultivated mungbean, which is determinate in habit. It is suggested that the introduction of the indeterminate trait into mungbean from the wild subspecies would increase the responsiveness of mungbean to favourable environments, analogous to that of black gram (V. mungo). Although the wild subspecies appeared more sensitive to cool temperature than cultivated mungbean, it may provide a source of tolerance to the warmer temperatures experienced during the wet season in the tropics.

Adaptive responses of wild mungbean (Vigna radiata ssp. sublobata) to photo-thermal environment. I. Phenology

The phenology of 11 diverse accessions of wild mungbean was observed under natural and artificial photoperiod–temperature conditions, in order to examine whether genotypic differences might be attributed to adaptive responses to photo-thermal conditions. There was large variation in phenological response among accessions and across environments, much of which was due to differences in the duration of the pre-flowering phase. Accessions that flowered earlier tended to flower for longer, apart from 2 earlier flowering, inland Australian lines that were also earlier maturing. The patterns of response in time from sowing to flowering over environment were consistent with quantitative short-day photoperiodic adaptation, a conclusion supported by the effects of artificial day-length extension and by ‘goodness of fit’ of the observed responses to standard models relating rate of development to photoperiod and temperature. The fitted models indicated that rate of development towards flowering was hastened by warmer temperatures, and delayed by longer day lengths, with differential sensitivity between accessions to both factors. The models also suggested that photoperiod was more important for accessions collected closer to the equator, which were generally later flowering as a consequence. Conversely, temperature was relatively more important in lines from higher latitudes. Modelling also suggested that the period from first flowering to maturity was sensitive to photoperiod and temperature. Again, longer days appeared to prolong growth and delay maturity. However, cooler temperatures accelerated rather than slowed maturity, by suppressing further vegetative growth. The variation observed indicated that there is considerable scope for using the wild population to broaden the adaptation of cultivated mungbean. In particular, the unusual response of a late-flowering, photoperiod-insensitive accession warrants further study to establish whether the wild population contains a unique ‘long juvenile’ trait analogous to that being used for improving phenological adaptation in soybean.

Acesso ao alimento artificial e enchimento do trato digestivo de juvenis do camarão marinho Litopenaeus vannamei (Boone) (Crustacea, Decapoda, Penaeidae) durante as fases clara e escura do período de 24 horas

The few data on the marine shrimp Litopenaeus vannamei (Boone, 1931 ) behavior related to feed offer in trays can result inadequate feeding by the animal, feed wastage and unnecessary nutrient input, increasing feed costs and potential environmental pollution of that culture. In order to provide tools for improved feed management methods in shrimp farms, a behavioral study was conducted, using 64 Litopenaeus vannamei juveniles (7,57 ± 1,01g), one animal per 33 m 2 . They were submitted to artificial photoperiods, half of them in reversed cycle, in order to register behavior during light and dark phases. The following variables were registered (continuous sampling) after feed exposition: a) latency to access the feeding tray, b) latency to start eating and c) digestive tract filling. The animals accessed the feeding trays and started consumption faster in the light phase hours. The digestive tract filling was higher half hour following feed offer, specially in the hours during the light phase.

Photoperiod in seawater influence seasonal growth and chemical composition in autumn sea-transferred Atlantic salmon ( Salmo salar L.) given two vaccines

Despite gains in commercial salmonid aquaculture production by using underyearling smolts (0+), poor performance in seawater has been noted. This study assesses how artificial photoperiods in seawater may improve the performance. Seawater-transferred 0+ Atlantic salmon were exposed to natural light (NL) or continuous light (LL) from October to midsummer, or to LL from October to January followed by natural light (LL–NL), or NL from October to January and then LL to midsummer. All fish experienced natural light after midsummer. The photoperiods changed the seasonal growth pattern and harvest weights became significantly different (LL: 3445 ± 46 g; NL–LL: 3207 ± 45 g; LL–NL: 3092 ± 56 g; NL: 2854 ± 42 g). Growth of NL fish decreased from autumn through winter and increased in spring. LL fish grew better than NL fish until spring and was 21% heavier at slaughter. Switching from LL to NL in January reduced growth rate from March onwards to a level slightly lower than the seasonal growth pattern of the NL fish. The onset of light in January (NL–LL) resulted in a temporary decrease in growth for 7 weeks followed by a major weight increase with growth rate being significantly higher than LL fish from late April until October. NL–LL fish never managed to catch up with the LL fish, but were significantly larger than the NL fish. Changes in condition factor with light treatment demonstrated clearly the photoperiodic influence on the seasonal growth pattern. Two vaccines were used in all photoperiods. The fish given the vaccine that gave least adherences (lesion score 1.8 vs. 2.3) became 20% heavier than those given the other vaccine, and no interaction between photoperiod and vaccine was observed. Muscle lipid and astaxanthin contents in June were highest in LL fish (lipid: 9.1%; astaxanthin: 4.4 mg kg − 1 ) and lowest in NL fish (lipid: 4.1%; astaxanthin: 2.6 mg kg − 1 ). These differences largely disappeared by November, although fish exposed to light following seawater transfer (LL and LL–NL) had a tendency to contain higher levels of astaxanthin than those on natural light (NL and NL–LL). Both lipid and astaxanthin contents in fillet correlated positively with fish weight. The incidence of sexual maturation was 4% in LL and LL–NL, 1.5% in NL and 0% in NL–LL. In the seawater-phase of underyearling autumn-transferred smolts, we recommend using the NL–LL photoperiod regime. This light treatment gave a slightly smaller fish than LL at harvest, but there were no losses due to sexual maturation.

Comportamento de Litopenaeus vannamei (Boone) (Crustacea, Decapoda, Penaeidae) em função da oferta do alimento artificial nas fases clara e escura do período de 24 horas

A escassez de dados acerca do comportamento do camarão marinho Litopenaeus vannamei (Boone, 1931) relacionado ao alimento artificial ofertado em comedouros poderá induzir a uma alimentação inadequada, aumentando a relação custo/benefício e os impactos ambientais potenciais do seu cultivo. Objetivando fornecer subsídios para a melhoria do manejo alimentar praticado nas fazendas, foram desenvolvidos estudos comportamentais utilizando 64 juvenis de L. vannamei (7,57 ± 1,01 g), submetidos a fotoperíodo artificial, metade deles em ciclo invertido, para observação das suas atividades durante as fases clara e escura. A ração foi oferecida em intervalos pré-estabelecidos, registrando-se antes e depois da oferta: exploração, natação, alimentação e inatividade (focal instantâneo). A natação ocorreu preferencialmente durante a fase escura. A alimentação foi mais elevada na primeira meia hora posterior à oferta, com ênfase nos horários da fase clara. O alimento artificial atuou, em ambas as fases, como um indutor da exploração do substrato, tornando os camarões mais ativos em todos os horários posteriores à sua oferta.

Plasma total T3 and T4 concentrations in bucks as affected by photoperiod

In order to determine whether total thyroxine (T4) and 3-3′-5-triiodothyronine (T3) plasma concentrations are affected by photoperiodic changes in bucks, these hormones were assayed using RIA in samples collected weekly for a year period in Alpine and Saanen male goats exposed to natural photoperiod (46°N latitude, control group), or to artificial photoperiod alternating every 2 months (4M group) or 1 month (2M) with long days (16L:8D) and short days (8L:16D). In the control group, the thyroid hormones showed marked seasonal variation. Maximal monthly peaks were recorded at the beginning of spring (April) for plasma T4 (35.7 ± 1.8 ng/ml) and in late winter to early spring (March) for plasma T3 (0.91 ± 0.11 ng/ml)—with the lowest concentrations being recorded in October (autumn) for plasma T4 (22.8 ± 1.0 ng/ml) and in September (late summer to early autumn) for plasma T3 (0.42 ± 0.01 ng/ml). In the 4M group, T4 plasma concentrations varied with daylength ( p < 0.05), recording an overall mean concentration significantly ( p < 0.01) higher during the short days (37.3 ± 7.5 ng/ml), than during long days (32.2 ± 7.3 ng/ml) with a significant effect of sampling time within each photoperiod ( p < 0.0001). In both light-treated groups, T3 varied with photoperiod ( p < 0.0001) and time ( p < 0.0001), increasing during long days and decreasing during short days. T3 plasma concentrations (derived from peripheral monodeiodination) followed the photoperiodic changes, while it was hypothesized that the stimulatory effect of daylength on T4 (thyroid gland secretory activity) was characterized by a longer latency period and could be seen in the 4M group during the following photoperiodic treatment. It is concluded that photoperiod affects thyroid hormone plasma concentrations in male goats, since different lighting regimes resulted in different profiles of both plasma T3 and T4. Bearing in mind the pivotal role of thyroid hormones in stimulating the metabolic activity of the whole body, it is possible that the light-induced increase in circulating hormones could sustain and improve animal production. The suitability of supplementary light treatments needs to be considered.

Effects of exposing boars to different artificial light regimens on semen plasma markers and “in vivo” fertilizing capacity

This study was designed to assess the effects of exposing boars to an artificial photoperiod on semen quality in terms of sperm concentration, sperm vitality, sperm motility and acrosome integrity. We also determined biochemical semen plasma variables, such as total protein concentration, phosphorylated tyrosine residues and fructose, glucose and sorbitol contents, along with their effects on the fertility, prolificacy and libido of the boars. Three groups of 10 males were kept for 3 months under experimental conditions of 24, 12 and 0 h of artificial light, and a constant temperature of 21 ± 1 °C and 60–75% humidity. The animals were fed a nutritious diet and subjected to semen collection twice per week. Semen samples were analyzed throughout the entire experimental period. Our results indicate that, while the extreme photoperiods (0 and 24 h of light) affected semen quality in terms of sperm concentration, acrosome integrity and semen volume, its fertilizing capacity was only significantly reduced under conditions of absolute darkness. Sperm motility was found to be a poor indicator of fertilizing ability, while other sperm factors, such as acrosome integrity or other functional variables seemed to behave better. The photoperiod was found to affect the production of accessory sex gland secretions more than their composition. In addition, light effects on fertility, prolificacy and libido seemed to be achieved through independent mechanisms.

Comparison of migratory tendency in European Quail Coturnix c. coturnix, domestic Japanese Quail Coturnix c. japonica and their hybrids

Since the 1970s, the decline of the occidental populations of European Quail Coturnix c. coturnix, a partial migrant Galliform species, has driven the release of domestic Japanese Quail Coturnix c. japonica into the wild as game birds. Recent experiments suggest that reproductive isolating mechanisms have not developed to prevent hybridization between European and Japanese Quail. To assess the potential impact of hybridization between the subspecies in the wild, this study aims to compare the migratory characteristics of captive European Quail, domestic Japanese Quail, F1 hybrids and a backcross. In a laboratory experiment, birds hatched in summer and reared under a natural photoperiod were transferred during winter to an artificial photoperiod (light–dark) of 14 : 10 h. Behavioural (migratory restlessness, crowing activity in males) and physiological (sexual development, fat accumulation, body mass) measures were recorded. Domestic Japanese Quail showed no migratory tendency in response to the increased day length. F1 hybrids showed rapid sexual development and few of them exhibited the typical profile of a migrant bird. Backcrosses showed great variation in their response, comparable with those of the European Quail. Therefore, hybridization could lead to an increased proportion of quail showing sedentary rather than migratory behaviour. Furthermore, hybrids that do show migratory behaviour have the potential to facilitate Japanese gene flow into areas where the release of domestic Quail as game birds is not yet practised.

Environmental control and adrenergic regulation of pineal activity in the diurnal tropical rodent, Arvicanthis ansorgei

Like nocturnal rodents, the diurnal tropical rodent Arvicanthis ansorgei shows a daily rhythm in pineal melatonin content. Seasonal and photoperiodic variations in the biosynthetic activity of the pineal gland: arylalkylamine-N-acetyltransferase (AA-NAT), hydroxyindole-O-methyltransferase (HIOMT) activities and melatonin content were measured in male and female A. ansorgei captured near Samaya, Mali, and kept either under artificial laboratory photoperiods [light-dark (LD) cycles: LD 14:10, LD 12:12 or LD 10:14 or caught in the field in Mali and killed at four different times of the year (January, April, June and November). Under artificial photoperiod, the duration of the nocturnal peak of AA-NAT activity and melatonin content increased with the duration of the dark period while the amplitude did not significantly change. In the field, annual variations in the amplitude of the nocturnal melatonin peak were observed with a maximum in April (highest temperature, low humidity and no grass availability, only seeds) and a minimum in November (high humidity, maximum green grass availability). The variations in the amplitude of the melatonin peak were not correlated with changes in AA-NAT HIOMT activities, suggesting that seasonal variations in the amplitude of the melatonin peak are not driven by these enzymes. Daytime injections of the beta-adrenergic agonist, isoproterenol, stimulated melatonin synthesis in January, April and June, but not in November. The annual differences in the amplitude of the melatonin peak as well as the seasonal differences in the response to an adrenergic stimulation suggest that environmental factors other than photoperiod, such as temperature, humidity and consequent food availability, could be important in the regulation of the annual variations in the pineal biosynthetic activity in this species.

Physiological responses in Nile tilapia exposed to different photoperiod regimes

After conditioning Nile tilapia Oreochromis niloticus for 2 weeks, the photoperiod regime of 12 tanks of fish was changed to a 6L : 6D photoperiod while 12 further tanks were retained on the conditioning photoperiod regime (12L : 12D). Blood samples were collected 3 days (first sampling) and 3 months (second sampling) after changing the photoperiod regime. Blood was collected at 6 h intervals from both photoperiod regimes (1000, 1600, 2200 and 0400 hours). At the first sampling time, fish in the 6L : 6D had significantly higher cortisol both in the light and dark phases than levels in fish in the 12L : 12D photoperiod. At the second sampling time, the levels were significantly higher only in the light phase. The levels of cortisol, glucose and Cl− in fish exposed to the 6L : 6D photoperiod, however, were far lower than those of acute stress‐induced levels observed in fish exposed to a stress experiment. Furthermore, there were no significant differences in overall values of all the variables between the photoperiod regimes at the second sampling time. This indicated that the fish exposed to the 6L : 6D photoperiod were not chronically stressed. Significantly higher blood lymphocyte counts were observed in fish exposed to the 6L : 6D compared to those of the 12L : 12D photoperiod during the light phase at the second sampling time. Other variables (glucose, Cl−, haematocrit and neutrophil) did not show a significant difference between the treatments at either sampling time. These results demonstrated that the artificial photoperiod regime did not cause a significant acute or chronic stress response in Nile tilapia.

Photosensitivity in body mass and testicular activity of brahminy myna, Sturnus pagodarum

This study analyzed photoperiodic sensitivity of brahminy myna (Sturnus pagodarum), which is a seasonally breeding bird species. During regression phase of the reproductive cycle (in early September), groups of myna were exposed to artificial photoperiods that were either close to or longer than those brahminy myna experiences at this time in wild at 29 degrees N. Following a 14-week exposure to such photoperiods (hours of light: hours of darkness; 13L:11D, 12L:12D, 11.5L:12.5D and 11L:13D), the birds were subjected to a longer day length (16L:8D) for another 9 weeks to test whether pre-treatment with varying photoperiods had an effect on subsequent long day photostimulation. There was a progressive increase in body mass under different pre-treatment photoperiods, with a faster increase in 11L:13D and 11.5L:12.5D than in 12L:12D and 13L:11D. When subjected to 16L: 8D, however, all groups showed decline in body mass. By contrast, the testes were not stimulated under 11L:13D and 11.5L:12.5D, and only one individual of the groups under 12L:12D and 13L: 11D showed a small testis recrudescence. All birds except one individual of the 13L:11D group, however, showed testis recrudescence when subjected to 16L:8D. These results suggest that body mass and testes have a different profile of photoperiodic response and appear to have two different threshold photoperiods for dissipating the post-reproductive refractoriness.

Reproductive activity in captive female Honey possums, Tarsipes rostratus, assessed by faecal steroid analysis

Hormonal changes associated with reproductive activity in the unique pollen and nectar-feeding marsupial Honey possum, Tarsipes rostratus, have been monitored by the measurement of sex steroids excreted via the faeces. From a radio-metabolism study, 63% of administered [ 14C]oestradiol was excreted in the faeces and 37% via the urine. Peak levels in the faeces were reached 6 h after injection and by a mean 12 h, 95% of steroid was eliminated. The principal metabolic products of progesterone that were identified by chromatographic analysis were the isomers 5α- and 5β-pregnan-3β-ol-20-one with only trace amounts of progesterone and the isomers 5β-pregnan-3β,20β- and 20α-diols. Extended excretory profiles for faecal progestagens (PM) and oestradiol-17β (E 2) are reported for the first time in a marsupial. The profiles from 4 females held in indoor cages with an artificial photoperiod suggest that long days inhibit reproductive activity in this species, as is the case in a number of other marsupials. One female appeared to resume cycling after a 5-month period and the time between peak levels of both E 2 and PM suggest that the length of the oestrous cycle in the Honey possum is approximately 25 days. The PM profile suggests that the corpora lutea secrete low levels of progesterone for approximately the first 19 days after ovulation, followed by increased rates of excretion during the final 6 days.