Combinations Of Photoperiod Research Articles

Growth and development of Virginia type groundnut cultivars under Mediterranean conditions

The growth and development of groundnut (Arachis hypogaea L.) are under the influence of complex environmental factors. Understanding of the growth responses of the groundnut to environmental factors may improve the application of better management practices and develop better cultivars to overcome the problems causing reductions in yield. A two-year field experiment was conducted to determine the growth and development response of groundnut genotypes to environmental factors in the eastern Mediterranean region of Turkey in 2001 and 2002. Time from sowing to physiological maturity (R8) ranged from 2513°Cd to 2588°Cd in 2001 and from 2514°Cd to 2573°Cd in 2002 while total calendar days varied between 147 and 153 and between 156 and 161 depending on genotypes in 2001 and 2002, respectively. Dry matter accumulation in each part of the plants continued until maturity although accumulation rate differed depending on plant age. Combination of suitable temperature and photoperiod during the reproductive stages resulted in continuous and abundant reproductive plant parts, which led to delayed harvest and increased unmarketable pods. The slower growth rate due to the cooler conditions during early stages caused slower biomass accumulation in successive stages indicating the importance of initial crop growth for final yield. Therefore, the genotypes having high initial growth rate, less reproductive organs, and shorter growing period should be developed for the Mediterranean conditions by breeders. The management studies should also deal with increased initial growth rate and reduced number of flowers, pegs or pods per plant. Based on our results, groundnut has a great yield potential under the Mediterranean conditions. However, further breeding and management studies are needed to improve the yield and profitability and reduce the complications arisen from the Mediterranean climate.

Environmental effects on asexual reproduction rates of the scyphozoan Aurelia labiata

Problem outbreaks of jellyfish and warming of the Earth's climate are both being reported at unprecedented rates. Models forecast continued changes in temperature, salinity, and solar radiation (insolation) in the world's oceans as consequences of global warming. Many species with a swimming jellyfish stage also have a benthic stage that asexually produces buds and new jel- lyfish (ephyrae). This perennial benthic stage probably determines the numbers of jellyfish in the population. In this study, polyps of the moon jellyfish Aurelia labiata from Puget Sound, Washington, USA, were tested in 9 combinations of temperature (7, 10, 15°C) and salinity (20, 27, 34) in the dark, and in 9 combinations of photoperiod (12, 8, and 4 h d -1 ) and light intensity (1 screen, 2 screens, opaque) at ambient salinity (27) and temperature (15°C). Another experiment tested polyps in treat- ments of 10, 15, and 20°C. Survival of the initial polyps in all treatments was high (83 to 100%). Tem- perature, salinity, and their combination dramatically affected the numbers of ephyrae produced (from nearly 0 at 7°C to 42 ephyrae polyp -1 at 15°C), the percentages of ephyrae out of total asexual reproduction (≤12% at 7°C to 89% at 20°C), and the delay before ephyra production (> 81 d at 7°C but only 39 to 46 d at 15°C). Thus, all results showed that more jellyfish were produced with increasing temperature. Long photoperiod and highest light intensity greatly accelerated strobilation, with polyps in 12 h light strobilating 30 to 40 d before those in other treatments. Polyps receiving the most light strobilated most frequently. In situ conditions showed that light increased much more rapidly than temperature before strobilisation, suggesting that light may be the more important signal. I sug- gest that the light-sensitive hormone melatonin, or a precursor like serotonin, coordinates the timing of strobilation in A. labiata with the seasonal light cycle.

Effects of plant growth substances on the conchocelis phase of Alaskan Porphyra (Bangiales, Rhodophyta) species in conjunction with environmental variables1

The effect of plant growth substances (PGSs) on conchocelis growth of Alaskan Porphyra (P. abbottiae V. Krishnam., P. pseudolanceolata V. Krishnam., P. pseudolinearis Ueda) was investigated. Growth was measured under different combinations of PGS concentrations (0, 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 ppm), PGS type (gibberellic acid, kinetin, and indole‐3‐acetic acid), temperature (7, 11, and 15°C), and photoperiod (16:8 light:dark [L:D] cycle and 8:16 L:D cycle). Plant growth substances effectively promoted the growth of Porphyra conchocelis. Depending on culture conditions, growth rates were increased relative to controls 6.9%–31.7% for P. abbottiae, 4.7%–25.7% for P. pseudolanceolata, and 8.9%–35.1% for P. pseudolinearis. Maximal growth of P. abbottiae occurred with 0.8 ppm kinetin, 15°C, and short‐day conditions (8:16 L:D). Porphyra pseudolanceolata exhibited maximal growth with 0.4 ppm indole‐3‐acetic acid, 7°C, and long days (16:8 L:D). Indole‐3‐acetic acid also effected maximal growth of P. pseudolinearis at 0.4 ppm, 15°C, and long‐day conditions (16:8 L:D). For P. abbottiae and P. pseudolinearis, intermediate PGS concentrations (0.4–1.6 ppm) had the greatest growth‐stimulating effects, whereas for P. pseudolanceolata, higher growth generally occurred at lower concentrations (0.1–0.8 ppm). Kinetin and indole‐3‐acetic acid had more influence on the conchocelis phase than gibberellic acid. The PGS concentrations greater than 1.6 ppm had a diminishing effect on growth, especially in P. pseudolanceolata. For P. abbottiae and P. pseudolinearis, higher temperatures resulted in higher growth rates, in contrast to P. pseudolanceolata, which grew faster at the lower temperatures.

Additive effects of advanced temperature and photoperiod regimes and LHRHa injection on ovulation in Atlantic salmon (Salmo salar)

In order to evaluate manipulation of spawning time as a potential means to extend 0+ Atlantic salmon (Salmo salar) smolt production in Tasmania, Australia, female salmon were exposed to a natural/simulated natural (42°S) photoperiod or an advanced (L:D 9:15) photoperiod from the austral summer solstice (20 December) under natural or advanced (~6 °C below natural temperature) temperature conditions. In late summer (26 February) injections of a commercial LHRHa preparation or vehicle (propylene glycol) commenced. Regular ovulation checks were conducted and ova were fertilised using milt from LHRHa-injected males held under matching photo-thermal conditions. Plasma levels of 17β-estradiol (E2) and testosterone (T) were monitored and reproductive success (cumulative % ovulation, % fertilisation and % survival to the eyed-egg stage) was recorded. Ovulations commenced first (09 March) in LHRHa-treated fish that experienced advanced photoperiod and thermal regimes whereas sham-treated fish exposed to natural photoperiod and temperature conditions where the last to ovulate (22 May–08 June). Treatment-related sequential changes in the timing of ovulations were reflected by sequential advances in the timing of peaks in plasma levels of E2 and T. The fertilisation of ova from LHRHa-treated fish that experienced advanced photoperiod and thermal regimes was significantly reduced (~52%) relative to all other treatments (>80%) but there were no significant treatment-related differences in the survivals of eggs to the eyed stage (~50–90%). Consequently, a maximum advance in the timing of median ovulation of 71 days and commercially acceptable eyed-egg yields were generated, demonstrating that combinations of photoperiod, thermal and hormone treatments may be employed to significantly extend spawning and thereafter increase the availability of 0+ smolts for grow-out.

Maternal photoperiod effect on and geographic variation of diapause incidence in Cotesia plutellae (Hymenoptera: Braconidae) from China

Effects of maternal photoperiod on the diapause trait of Cotesia plutellae in two populations, one from Hangzhou (30°14′ N), Zhejiang Province, and the other from Changchun (43°52′ N), Jilin Province, China, were examined in the laboratory by exposing the mother generation (G0) to 3 day-lengths (8L-16D, 12L-12D, and 16L-8D) at 25°C, and exposing their offspring (G1) to 2 day-lengths (8L-16D, 11L-13D) at 4 temperatures (13, 15, 17, 20°C). All three diapause-inducing factors had a significant influence on the incidence of diapause. Both populations could be induced to enter diapause under pertinent conditions. Long day length in G0 decreased the incidence of diapause and lowered the critical temperature for diapause-induction in G1. There were significant differences in the incidence of diapause between the two populations in almost all combinations. Compared to the southern Hangzhou population, the northern Changchun population produced a higher proportion of diapause individuals, and had higher critical temperatures for diapause-induction in all 6 photoperiod combinations used in G0 and G1 except for the one in which short day length (8L-16D) was used in both generations.

Effects of photoperiod and temperature on preimaginal development and summer diapause of Chrysocharis pubicornis (Zetterstedt) (Hymenoptera: Eulophidae), a pupal parasitoid of leafminers (Diptera: Agromyzidae)

The preimaginal development of Chrysocharis pubicornis was studied at different temperatures and 14L:10D photoperiod. The lower developmental threshold was 7.4 and 7.2°C, and the thermal constant was 297.4 and 307.5 degree-days for males and females, respectively. The effects of combinations of different temperatures and photoperiods on larval diapause induction and termination were also examined. Larval development showed a short-day type response affected by temperature. The percentage of individuals entering diapause increased with the temperature and photoperiod. The critical photoperiod for diapause induction was between 12 and 14 h at 25°C, whereas at 15 h and 20°C the diapause rate did not reach 50% within the photoperiod range tested. Regardless of the photoperiod, diapause terminated at 15°C but was maintained at 25°C. At 20°C, 90% of individuals terminated diapause at 12 h photoperiod but only 16% at 16 h photoperiod. A significant effect of the photoperiod on the post-diapause emergence pattern of wasps was observed at 15°C. From these results, it is considered that summer diapause enables C. pubicornis to synchronize its occurrence with that of the garden pea leafminer, Chromatomyia horticola.

Duration from vine emergence to flowering suggests a long-day or rate of change of photoperiod response in white yam ( Dioscorea rotundata Poir.)

The objective of this study was to quantify the effect of photoperiod on the duration from vine (shoot) emergence to flowering in white or Guinea yam ( Dioscorea rotundata). The duration from vine emergence to flowering in two clonal varieties of yam (TDr 131 and TDr 99-9) was recorded at 10 different sowing dates/locations in Nigeria. Durations to flowering varied from 40 to >88 days. Mean daily temperature and photoperiod between vine emergence and flowering varied from 25 to 27 °C and 13.1 to 13.4 h day −1, respectively. Both clones had similar responses to temperature, with base and optimum temperatures of 12 and 25–27 °C, respectively. Thermal durations to flowering were strongly related ( r 2 > 0.75–0.83) to absolute photoperiod (h) at vine emergence as well as to rate of change of photoperiod (s day −1) at vine emergence. The response to absolute photoperiod suggests that white yams are quantitative LDPs, flowering sooner in long than short days. Yams also flowered earlier when the rate of change of photoperiod was positive but small, or was negative. It is suggested that yams may use a combination of photoperiod and rate of change in order to fine tune flowering time.

Influence of Light Intensity, Photoperiod, and Temperature on the Efficacy of Two Aphelinid Parasitoids of the Greenhouse Whitefly

In short-term laboratory experiments, we studied the influence of light intensity, photoperiod, and temperature on the feeding and oviposition activity of two aphelinid parasitoids, Encarsia formosa Gahan and Eretmocerus eremicus Rose and Zolnerowich, on the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). E. eremicus parasitized significantly more whitefly hosts than E. formosa in all treatment combinations of light intensity and photoperiod at 24 and 20°C. At 24°C, both E. formosa and E. eremicus parasitized approximately twice as many whitefly hosts at the high light intensity (112–114 W/m2)–long daylength (L 16:D 8 h) treatment than at the low light intensity (12–14 W/m2)–short daylength (L 8:D 16 h) treatment. In most instances at 20 and 24°C, significantly more dead whitefly hosts were recorded in leaf cages introduced with parasitoids than leaf cages with no parasitoids, indicating that host feeding occurred. Both E. formosa and E. eremicus parasitized significantly more whitefly hosts under the simulated summer (i.e., high light intensity [82.0–83.6 W/m2]; long daylength [L 16:D 8 h], 24°C) treatment than the winter (i.e., low light intensity [10.8–11.1 W/m2]; short daylength [L 8:D 16 h], 20°C) treatment. In addition, significantly more dead whitefly hosts were observed in leaf cages introduced with E. eremicus than E. formosa under the winter treatment, suggesting that E. eremicus killed more whitefly hosts through host feeding than E. formosa. This was not the case for the other treatment combinations. E. eremicus contributes more to greenhouse whitefly mortality than E. formosa by a combination of greater parasitism and host feeding and therefore is recommended for use in winter months with day temperatures ≥ 20°C, in addition to later in the season, where it is currently being used.

Nymphal and adult performance of genetically determined types of Nezara viridula (L.) (Heteroptera: Pentatomidae), under different temperature and photoperiodic conditions

The southern green stink bug, Nezara viridula (L.), has several genetically determined types, three being the most common in Brazil: G (f. smaragdula - green body), O (f. torquata - green body with lateral and median lobes of the head and anterior margin of the pronotum yellow), and Y (f. aurantiaca - gold or orange body). Nymphal and adult performance of these types was studied at 15ºC/10hL, 22ºC/12hL, and 29ºC/14hL. Mean total nymph mortality in all types at 15ºC/10hL was high (ca. 80%), especially for type G (98%); at 22ºC/12hL, the greatest mortality (55%) occurred in type G, and at 29ºC/14hL in type Y (65%). In general, at combinations of higher temperatures and longer photoperiods, nymphs developed faster. Adult longevity of type G decreased from ca. 88 days at 15ºC/10hL to ca. 57 days at 22ºC/12hL and 29ºC/14hL; for type O, adult longevity varied from ca. 81 days at 22ºC/12hL to ca. 55 days at 29ºC/14hL; type Y showed the shortest lifespan, in particular at the extremes of temperatures/photoperiods (< 20 days). Types G and Y did not reproduce at 15ºC/10hL, and type Y did not reproduce at 29ºC/14hL; type O reproduced at all three abiotic conditions. These results demonstrate that type O is the most adapted to the cooler temperature and shorter photoperiod, which explains its greater abundance in south Brazil.

The seasonal forms and reproductive potential of the common pistachio psylla, Agonoscena pistaciae (Hem., Psylloidea)

Abstract: Two distinct seasonal forms were found for the common pistachio psylla, Agonoscena pistaciae, the most serious insect pest of cultivated pistachio trees, Pistacia vera in Iran. The two forms are different morphologically as well as biologically. The summer form is of light colour and readily mates and starts egg laying 1–2 days after emergence, whereas, the winter form is larger, generally darker and in reproductive diapause. The first form is observed under long photoperiod, while the second form is induced under a combination of short photoperiod and low temperature. The combination of long photoperiod and warm temperature enhanced post‐emergence ovarian development in the winter form, showing a close inverse correlation between pre‐oviposition period and increasing temperatures. Both forms of A. pistaciae are adapted to a wide temperature range of 20–30°C for reproduction, and the fecundity of psyllid adults of either summer‐ or winter forms was found to be very high under experimental conditions.

Photoperiod during stem elongation in wheat: is its impact on fertile floret and grain number determination similar to that of radiation?

Increasing duration of stem elongation by exposure to short photoperiod would result in higher spike dry weight at anthesis, which is positively associated with the number of fertile florets and grains in wheat. However, it is not easy to determine whether photoperiod effects on fertile florets and grains are only mediated by assimilate supply to the growing spike when spike weight variation is attained only with photoperiod treatments. The aim of this study was to determine whether photoperiod effects on number of fertile florets and grains may be direct, that is, not mediated by assimilate supply, by comparing the magnitude of photoperiod effects with those of shading the canopy. Spike dry weight at anthesis was changed through the factorial combination of different photoperiod (natural and 6 h extended photoperiod) and shading (un-shaded and 67 ± 3% shaded) treatments during stem elongation of Buck Manantial, a cultivar known for its photoperiod sensitivity in this phase. Both treatments modified spike dry weight at anthesis and the number of fertile florets and grains, independently. When duration of stem elongation was lengthened by exposure to natural photoperiod and when incident radiation was high, spike dry weight at anthesis increased by 33% (NP+0 v. NP+6) and 27% (un-shaded v. shaded), respectively. The number of fertile florets increased similarly to spike dry weight (34% NP+0 v. NP+6 and 28% un-shaded v. shaded) resulting in higher number of grains. Most photoperiod effects on the number of fertile florets and, consequently, on the number of grains, were mediated by assimilate supply to the growing spike as the same relationship between the number of fertile florets and spike dry weight at anthesis was observed for photoperiod and shading treatments (R2 = 0.99, P<0.05).

Hatching of cladoceran resting eggs: temperature and photoperiod

Summary 1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages.2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 °C. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination.3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species.4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 °C should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n = 100) can be selected from the total hatchling assemblage.

Interactive effects of photoperiod and temperature on diapause induction and termination in the yellow‐spotted longicorn beetle, Psacothea hilaris

Abstract. The interactive effects of temperature (20 °C or 25 °C) and photoperiod (LD 12 : 12 h or LD 15 : 9 h) on diapause induction and termination are investigated in the west‐Japan type yellow‐spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae). Larval diapause of P. hilaris is induced under three diapause‐inducing conditions (20 °C–SD, 20 °C–LD and 25 °C–SD), and the diapause larvae are transferred to one of four conditions (20 °C–SD, 20 °C–LD, 25 °C–SD or 25 °C–LD) for observation of pupation, which indicates termination of diapause. The intensity of diapause induced under the three conditions increases in the order 20 °C–SD &lt; 25 °C–SD &lt; 20 °C–LD, when assessed by the time course of pupation after the transfer. On the other hand, the effectiveness of the temperature–photoperiod combinations to terminate diapause is in the order 25 °C–SD (ineffective) &lt; &lt; 20 °C–LD &lt; 25 °C–LD &lt; 20 °C–SD. Among the temperatures (5, 10, 15 and 20 °C) examined, 15 °C is the most effective in terminating diapause under the short day; diapause in most larvae appears to have been completed in 15 days.

Photothermal impact on maize performance: a simulation approach

Crop simulation models can be robust tools to help develop an understanding of a plant’s response to a given set of weather and soil conditions and the interaction with various crop management scenarios. This study was conducted to simulate controlled-environment conditions using the CERES-Maize model to obtain a quantitative understanding of different maize cultivar responses to a range of temperature and photoperiod combinations. Nine-day length treatments ranging from 8 h to 16 h, together with minimum temperature ( T min) treatments ranging from 5 °C to 35 °C and maximum temperature ( T max) treatments ranging from 15 °C to 45 °C, were applied to nine maize ( Zea mays L.) cultivars. Increasing T max up to 35 °C at any given T min enhanced biomass production for all cultivars; a further increase of T max above 35 °C had a negative impact on biomass. Increasing temperature also accelerated developmental rates for both anthesis and maturity. An identical mean temperature obtained from various T min or T max combinations resulted in a different crop performance, indicating specific responses to either high or low values of T min or T max. The highest potential yield levels were found at rather low temperature combinations of a T max of 20 °C and a T min of 10 °C; yield varied from 10.2 t ha −1 to 23.2 t ha −1 for these conditions, mainly caused by extremely long growing seasons. Photoperiod showed no effect across all treatments, due to a low sensitivity to changes in day length for the cultivars used in this study. It can be concluded that crop simulation models can help provide an understanding of weather and crop interactions for a complex environment that are rather difficult to conduct under controlled-environment conditions and are resource intensive.

Bands of root hairs are produced in tomato (Lycopersicon esculentum) in response to specific combinations of thermoperiods and photoperiods

Tomato (Lycopersicon esculentum) seedlings were grown in non‐aerated culture solution in a controlled environment under 10 different combinations of photoperiod and thermoperiod. It was found that the pattern of distribution of root hairs was controlled by the photoperiod and thermoperiod. Under a diurnal rhythm consisting of a 16/8 h photoperiod, at temperatures of 25°C/15°C, regions of the root had bands of hairs that were separated by hairless regions. After 5 days under these conditions, four bands of hairs were most commonly found. Other combinations of light and temperature also gave rise to bands of root hairs, but the bands were fewer and less defined. A lower night temperature, together with 8 h of darkness, switched off root‐hair production. These findings are consistent with the hypothesis that all epidermal cells in tomato are “switched on” for hair production, but that this state can be altered by specific environmental conditions.

Dependence of photoperiodic response of growth cessation on the stage of development in Picea abies and Betula pendula seedlings

Dependence of photoperiodic response of growth cessation on the stage of development was examined in seedlings of Norway spruce ( Picea abies (L.) Karst.) and silver birch ( Betula pendula Roth) in greenhouses with 20 °C day and 10 °C night temperatures. Different combinations of photoperiod and stage of development were created by repeating sowing five times with 2 week intervals during the summer. During the experiment light conditions were natural but the daily temperature sum accumulation was regulated to be constant. Eight origins of spruce and seven origins of birch from different latitudes (60–67°N) in Finland were used. In the first growing season both Norway spruce and silver birch seedlings from the first sowings required a longer time for growth cessation than seedlings from the later sowings. However, because the seedlings from the first sowings ceased their growth on an earlier calendar date, the night length at the time of growth cessation was shorter for the seedlings from the first sowings. The results suggest that the variation in the timing of growth cessation of Norway spruce and silver birch seedlings during the first growing season was explained jointly by night length and stage of development. Seedlings from northern origins stopped their growth with shorter night length than those from southern origins. The effects of latitude and average temperature sum of the original growing site on the critical night length of growth cessation in the first growing season were stronger in Norway spruce than in silver birch. In the second growing season the sowing time did not affect the timing of the formation of the terminal buds, but slightly affected the timing of height growth cessation of Norway spruce and silver birch seedlings.

The effect of photoperiod and temperature on the reproduction of European sea urchin Paracentrotus lividus

The effects of water temperature and light regimes on gonadal development in the sea urchin Paracentrotus lividus were evaluated in two 12-week periods, one in spring–summer and one in winter–spring. Four different combinations of photoperiod and temperature regimes (18–26 °C) were tested in each. Sea urchins were fed a prepared diet. Food intake, growth, gonadosomatic index, biochemical composition and gametogenetic stages were measured. Results show that water temperatures between 18 and 22 °C enhance growth and gonadal development. Long days (illumination) reduce the rates of gametogenesis while short days increase reproductive development.

Distribution, abundance and phenology of two species of Liagora (Nemaliales, Rhodophyta) in northern Spain

Liagora viscida and L. distenta grow on small boulders in rockpools at Campiello (Asturias, north-west Spain). This coast forms the northern limit of the geographical distribution of L. distenta in the north-east Atlantic. Gametophytes of both species were only evident from June to October. From June onwards, they increased in abundance, reaching a maximum that never exceeded 15% cover. Significant correlations were found for L. viscida and L. distenla between percentage cover and both sea water temperature and photoperiod. The entire population disappeared at the end of summer, after carpospore release. Gametophytic plants of L. viscida appeared in early June and all plants examined were females bearing carposporophytes. No male thalli were observed. In L. distenla, formation of the carpogonial branch took place in mid-June. Male thalli of L. distenla were observed between mid-June and early September. Under laboratory culture conditions, both species formed carpospores that germinated into filamentous tetrasporophytes. No tetrasporangia were observed but monosporangia were frequent under different combinations of temperature and photoperiod. Monospores germinated into further filamentous sporophytes. These data, and the fact that both species reappear every year in the same sites, suggest that L. dislenla and L. viscida have a L. Jarinosa-type life history.

Maturation and spawning performance of pond-rearedPenaeus merguiensisin different combinations of temperature, light intensity and photoperiod

The combined effects of temperature (23 and 27 °C), light intensity (1100 and 2 lux or ≈ 21.5 and 0.04 μEinst m−2 s respectively) and photoperiod (10 h light/14 h dark and 14 h light/10 h dark) on ovarian maturation and spawning performance of ablated pond-reared Penaeus merguiensis were investigated in a 51-day experiment. The results showed that temperature was the most influential factor, followed by light intensity, whereas the effect of photoperiod was minor. As the maturation process progressed, the effects of temperature and light intensity became stronger while that of photoperiod became less significant. Temperature significantly affected all the reproductive parameters assessed. Prawns in the 27 °C treatments outperformed those in the 23 °C treatments (P < 0.05). The effect of light intensity was found to have a significant effect (P < 0.05) only on the proportion of spawners (prawns that spawned) and spawning rate. More prawns spawned at a higher rate under dim light (2 lux) than under strong light (1100 lux). Photoperiod affected only the proportion of prawns reaching stage III of ovarian development (P < 0.05). There were interactions between temperature and light intensity affecting the proportion of prawns reaching stage III and, although not significantly, the proportion of spawners (P = 0.177), fecundity (P = 0.134) and survival (P = 0.061). Overall, it is recommended that a combination of 27 °C, 2 lux and 10 h light/14 h dark is suitable for the maturation of pond-reared P. merguiensis. There were indications that temperature can be used to control the rate of ovarian maturation. Also, it is possible to increase light intensity up to 1100 lux in P. merguiensis hatcheries if prawns are ablated.

Shifting the natural spring–summer breeding season of the Australian freshwater crayfish Cherax quadricarinatus into the winter by environmental manipulations

Ninety sexually mature Cherax quadricarinatus females were exposed to various combinations of photoperiod and temperature for 2 months during the summer. Females were randomly assigned to either “winter” “semi-winter” or “summer” simulation treatments. In the “winter” treatment, crayfish were exposed to a simulated winter photoperiod (gradual decrease from 14L:10D to 10L:14D, 4 weeks at short day length followed by gradual increase to 14L:10D) and temperature (gradual decrease from 27 to 15 °C, held for 4 weeks, and then gradual increase to 27 °C). In the “semi-winter” treatment, crayfish were exposed to a simulated winter photoperiod and a summer temperature (27–29 °C). In the “summer” treatment, the crayfish were exposed to summer water temperatures and a photoperiod of 14L:10D. Following the 2 months of conditioning, the females were stocked for 7 months in small groups with males under environmental conditions similar to those of the “summer” treatment. All females were individually tagged and molting and spawning events were monitored. Females exposed to “semi-winter” conditioning in the summer, demonstrated a threefold increase in the rate of first spawning during the winter (December–February) compared with the other females. Crayfish breeders can easily implement these findings since shifting the breeding season into the winter only requires shortening of the photoperiod in the summer. The stocking of ponds in the spring with large nursed juveniles that hatched from eggs spawned in the winter, would allow the attainment of market size at the end of the limited growout season in temperate zones.