光照强度与光周期对虎斑乌贼胚胎发育的影响

为探究光照对虎斑乌贼受精卵孵化的影响,确定其胚胎发育的最佳光照条件,本研究采用单因子试验方法,分析了不同光照强度(10、30、50、70、90 μmol·m^-2·s^-1)和光周期L∶D(24 h∶0 h、18 h∶6 h、12 h∶12 h、6 h∶18 h、0 h∶24 h)对虎斑乌贼胚胎发育的影响.结果表明: 不同光照强度对虎斑乌贼胚胎发育的孵化率、卵黄囊断裂率、培育周期、初孵幼体体质量与胴长均影响显著;而对孵化周期和幼体出膜7 d后存活率无显著影响.其中孵化率、培育周期、初孵幼体体质量与胴长随着光照强度的增强先增大后减小,而卵黄囊断裂率则逐渐增大.最适光照强度为30 μmol·m^-2·s^-1,此光照强度下孵化率为(90.0±4.1)%,卵黄囊断裂率为(7.3±1.5)%,培育周期为(25.50±0.35) d,孵化周期为(8.10±0.89) d,初孵幼体体质量为(0.213±0.011) g,胴长为(1.013±0.022) cm,出膜7 d后存活率为(97.1±4.0)%.不同光周期对虎斑乌贼胚胎发育的孵化率、培育周期、孵化周期均影响显著,而对卵黄囊断裂率、初孵幼体体质量、胴长和幼体出膜7 d后存活率无显著影响.其中孵化率和孵化周期随着光照时间的增加呈现先增大后减小的变化.最适光周期为LD(12 h12 h),此光周期下孵化率达(88.7±1.8)%,卵黄囊断裂率为(8.7±1.8)%,培育周期为(25.00±0.50) d,孵化周期为(7.00±3.20) d,初孵幼体体质量为(0.209±0.005) g,胴长为(0.998±0.026) cm,出膜7 d后存活率为(96.8±7.1)%.说明弱光照强度30 μmol·m^-2·s^-1和半日光照强度L∶D(12 h∶12 h)更有利于虎斑乌贼的胚胎孵化.在实际生产中,应避免阳光直射,采取适当的遮光措施.     

Schooling behaviour of juvenile Pacific bluefin tuna Thunnus orientalis depends on their vision development

The effects of vision development and light intensity on schooling behaviour during growth in juvenile Pacific bluefin tuna Thunnus orientalis were investigated using both behavioural and histological approaches. The schooling behaviour of three age groups [25, 40 and 55 days post hatching (dph)] of juvenile T. orinetalis were examined under various light intensities. Subsequently, schooling variables, such as the nearest neighbour distance (D(NN) ) and the separation swimming index (I(SS) ), were also measured under different light intensities. Furthermore, retinal indices of light adaptation in juvenile fish at each experimental light intensity and visual acuities in six stages (25-55 dph) of juveniles were examined histologically. During growth, the light intensity thresholds of I(SS) decreased from 5 to 0·05 lx, and D(NN) under light conditions (>300 lx) also decreased from 9·2 times the standard length (L(S) ) to 1·2 times L(S) . The thresholds of light intensities for the light adaptation of retinas in juveniles (25-55 dph) similarly decreased from 5 to 0·05 lx with growth. In addition, the visual acuities of juveniles developed from 0·04 to 0·17 with decreasing D(NN) . These data clearly indicate that the characteristics of schooling behaviour strongly correspond to the degree of vision development. Juvenile T. orinetalis also appear to be more dependent on cone rather than rod cells under low light intensity conditions, resulting in a relatively high light intensity threshold for schooling. These results suggest that juveniles can adapt to darker conditions during growth by developing improved visual capabilities.     

Effects of light intensity and addition of carotene rich Dunaliella salina live cells on growth and antioxidant activity of Solea senegalensis Kaup (1858) larval and metamorphic stages

Senegal sole Solea senegalensis larval and metamorphic stages were exposed to a range of light intensities (200, 1000 and 2000 lx) in cultures with or without supplementation of β-carotene-rich live Dunaliella salina cells. Antioxidant biomarkers such as superoxide dismutase (SOD), catalase (KAT), total glutathione peroxidase (t-GPX) and malondialdehyde (MDA) were determined in larval and metamorphic stages. Growth was not affected ( P > 0·05) either by light intensity or D. salina supplementation. Survival after metamorphosis was also unaffected by D. salina supplementation (mean ± s . e . 81·0 ± 2·5% against 80·6 ± 2·9% those fed the control algal diet) or light intensity (mean ± s . e . 74·3 ± 4·9% for 200 lx, 85·1 ± 2·7% for 1000 lx and 82·8 ± 5·2% for 2000 lx, respectively). Light intensity affected ( P < 0·05) KAT and t-GPX throughout development. SOD was only affected in metamorphosing larvae. The highest KAT and t-GPX activities were detected when the lowest light intensity (200 lx) was used. Light had no effect ( P > 0·05) on MDA at any stage. Supplementing the diet with D. salina did not affect SOD, KAT or t-GPX and there was no interaction ( P > 0·05) with light intensity. MDA was the only biomarker whose activity was significantly ( P < 0·05) reduced when D. salina was supplemented to the larval rearing tanks. The effect of D. salina supplementation was only detected in metamorphosing larvae, whose MDA levels were noticeably higher than in earlier stages. These results are evidence of the antiperoxidative effect of β-carotene from live algae in the larval rearing process of marine fishes.     

Schooling behaviour and retinomotor response of juvenile Pacific bluefin tuna Thunnus orientalis under different light intensities

Schooling behaviour and histological retinal light adaptation in juvenile Pacific bluefin tuna Thunnus orientalis were examined under various light intensities to determine the effect of light intensity on behaviour. After monitoring the schooling behaviour of juveniles 35–36 and 45–46 days post hatching, schooling variables such as nearest neighbour distance and separation swimming index were measured under different light intensities. Furthermore, retinal indices of light adaptation were investigated histologically for each experimental light intensity. Under intensities >5 lx, schooling variables in the two juvenile growth stages were nearly constant, allowing schooling. In contrast, the schooling variables indicated that the fish gradually swam more widely and randomly with decreasing light intensities <5 lx. The retinal indices also showed a shift from light adaptation to dark adaptation at light levels <5 lx. From 5 to 0·01 lx, retinal adaptation and fish schooling behaviour changed with light intensity. These data suggest that the schooling behaviour of juvenile Pacific bluefin tuna is greatly affected by retinal adaptation.     

大蒜对菲律宾蛤仔早期生长发育的影响

实验了不同大蒜汁浓度(0、2、4、8、16、32 mg/L)对菲律宾蛤仔受精卵孵化率,幼虫生长、存活、变态及稚贝生长与存活的影响,总结了室内大规模人工育苗过程中大蒜防病效果。结果表明:随着大蒜汁浓度的增加,孵化率降低;大蒜汁浓度达到16mg/L,胚胎发育延迟;达到32mg/L,受精卵不能孵化为正常幼虫。浮游期间,幼虫的生长受大蒜汁抑制,幼虫的存活率则随着大蒜汁浓度增加先升高后降低;幼虫的变态率随着大蒜汁浓度的增加先升高后降低,以16mg/L为最适浓度;变态规格随着大蒜汁浓度增加而减小。室内培育期间,稚贝生长与存活随着大蒜汁浓度的增加先升高后降低,以8mg/L为最适浓度;室内大规模人工育苗过程中,使用浓度为8-10mg/L大蒜汁可以起到较好的防病效果。     

To hatch or not to hatch? Egg hatch response to larval density and to larval contact in a treehole mosquito

Abstract.

• 1 We investigated the effect on egg hatch of exposure to: (1) varying larval density, and (2) larval contact in Aedes triseriatus Say (Diptera: Culicidae). For 2 days in the laboratory we submerged eggs into a treehole water medium containing 0 (control), 4, 12 or 24 larvae that could either contact the eggs directly or were separated from them by a screen. Following treatment, abundance of microorganisms on the egg surfaces, a food source for newly hatched larvae and a proposed hatching stimulus, was assessed by counts made from serial dilutions of samples.
• 2 We discovered a complex hatching response to larval contact and to larval density, and an interaction between these two factors in their effect on microbial growth. Hatching was inhibited in the 0-larva control, even though microorganisms grew abundantly on the eggs. Hatch rate, as well as microbial counts, were high for eggs in direct contact with 4 larvae. As density increased in the larval contact treatment, microorganisms disappeared from the egg surfaces and hatch rate declined.
• 3 When protected from larval grazing, eggs supported numerous microbial colonies irrespective of larval density. In contrast to the contact treatment group, egg hatch increased with increasing larval density. These observations suggest that the combination of microbial growth and a larval factor stimulates hatch. This hatching response may have evolved because both abundant microorganisms and numerous larvae reflect a habitat of good quality.

     

Effect of light periodicity and intensity on the growth and survival of Heterobranchus longifilis Val. 1840 (Teleostei: Clariidae) larvae after 14 days of rearing

Heterobranchus longifilis Val. 1840 larvae were reared under two light intensities, 30 lux and 915 lux, and at varying photoperiods. Results show that maximum survival (82.5 ± 6.5% respectively) at 30 lux was obtained at continuous illumination [24 h light (L)], while the minimum (65 ± 21.2%) was at the 6 h L : 18 h dark (D) treatment. Survival at 24 h D averaged 71.3 ± 6.3%, with no significant difference (P < 0.05) in growth of larvae. Maximum larval survival at 915 lux was 87.5 ± 17.7% at the 18 h L treatment. Growth was not significantly different (P < 0.05) in the treatments. Comparison of the two light intensities showed that survival was better at a photoperiod above 12 h irrespective of intensity, while growth was significantly better at the 915 lux intensity.     

幼虫密度对马铃薯块茎蛾生长发育及繁殖的影响

室内观察了块茎中不同虫口密度(5、10、15、20、25、30头/块茎)对马铃薯块茎蛾Phthorimaea operculella(Zeller)生长发育、后代发育和繁殖的影响。结果显示:幼虫密度显著影响马铃薯块茎蛾的生长发育及繁殖。对其生长发育影响的结果表明:幼虫的发育历期(7.1～9.1d)、蛹的历期(8.8～9.9d)、雌雄成虫的历期(分别为6.4～12.9d,6.7～11.6d)随幼虫密度的增加而延长;幼虫存活率(70.3%～93.3%)、蛹的羽化率(69.8%～91.7%)随幼虫密度的增加显著下降;单头蛹重(9.2～11.4mg)、单雌产卵量(136.8～166.0粒)、成虫的雌∶雄比(0.54～2.17)随幼虫密度的增加而下降。对其后代发育及繁殖的影响的结果表明:卵的发育历期(3.0～4.4d)、幼虫的发育历期(6.2～10.8d)、蛹的历期(8.1～10.0d)、雌雄成虫的历期(分别为7.4～11.8d,6.6～10.5d)、世代发育历期(24.4～36.1d)随幼虫密度的增加而从延长;卵的孵化率(73.1%～79.0%)、幼虫存活率(55.0%～96.8%)、蛹的羽化率(63.3%～93.3%)、世代的存活率(25.6%～71.5%)随虫口密度的增加而下降;单头蛹重(8.9～9.9mg)、单雌产卵量(93.5～155.6粒)、成虫的雌∶雄比(0.45～2.20)随虫口密度的增加而下降;种群趋势指数(I)(7.44～76.43)随幼虫密度的增加而下降。马铃薯块茎蛾的饲养密度建议以1头/13.0～26.0g块茎为宜。     

Effets du retard dans la première alimentation sur le développement de la larve planctotrophe de l'oursin Paracentrotus lividus

The growth of the skleleton and changes in biochemical constituents (proteins, carbohydrates and lipids) were observed in embryos (days 0 and 1) and larvae (2-8 days) of the sea urchin Paracentrotus lividus that were starved (C 0) or fed low (1,000 cells of Hymenomonas elongata, C 1) or high (5,000 cells, C 5). Different batches of C 1 and C 5 larvae were fed first the 2nd, 3rd, 4th or 5th day after fertilization. Initiation of feeding 24 h after hatching slowed down the rate of increase in length of the larval appendages. A differential growth of skeletic rods (somatic and postoral rods) and variations in proteins weights shows the existence of a mixotrophic phase between endotrophic and planktotrophic phases. Best development occured in larvae which were first fed at the lower food level 24 h after hatching. On the 2nd and the 3rd day the somatic/postoral rod ratio is ≥1. This higher ration can be used to estimate the age of natural populations of larvae.     

Carry‐over effects of multiple stressors on benthic embryos are mediated by larval exposure to elevated UVB and temperature

Damaging effects of UVB in conjunction with other stressors associated with global change are well‐established, with many studies focused on vulnerable early life stages and immediate effects (e.g., mortality, developmental abnormalities). However, for organisms with complex life cycles, experiences at one life stage can have carry‐over effects on later life stages, such that sublethal effects may mediate later vulnerability to further stress. Here, we exposed embryos in benthic egg masses of the New Zealand intertidal gastropod Siphonaria australis to treatments of either periodic stress (e.g., elevated UVB, salinity, and water temperature mimicking tidepool conditions in which egg masses are commonly found during summer) or control conditions (low UVB, ambient salinity, and water temperatures). Although there was high mortality from stressed egg masses, 24% of larvae hatched successfully. We then exposed the hatching larvae from both egg mass treatments to different combinations of water temperature (15 or 20 °C) and light (high UVB or shade) 12 h per day for 10 days. The most stressful larval conditions of 20 °C/high UVB resulted in low survival and stunted growth. Carry‐over effects on survival were apparent for shaded larvae exposed to elevated temperature, where those from stressed egg masses had 1.8× higher mortality than those from control egg masses. Shaded larvae were also larger and had longer velar cilia if they were from control egg masses, independent of larval temperature. These results demonstrate that previous experience of environmental stress can influence vulnerability of later life stages to further stress, and that focus on a single life stage will underestimate cumulative effects of agents of global change.     

The combined effects of temperature and salinity on hatching success and the survival,growth, and development of the larval stages of Metapenaeus bennettae (Racek & Dall)

During the spawning season of the estuarine prawn Metapenaeus bennettae (Racek & Dall), laboratory and field experiments were conducted to examine the combined effects of temperature and salinity on hatching success of eggs and the survival, growth and development of larvae. Response surface analysis showed that optimal levels of temperature and salinity for maximum hatching success varied depending on conditions during spawning. Similarly, temperature and salinity conditions that produced maximum survival and growth of larvae depended on conditions during rearing prior to experimental temperature/salinity treatments. At the onset of feeding, larvae showed the lowest tolerance to changes in temperature and salinity. Supplementary feeding experiments in the laboratory, and survival rates in field experiments indicated that starvation was a more potent factor than the effects of temperature and salinity in determining survival through the protozoeal larval stages. Late larval stages were relatively indifferent to the effects of temperature and salinity. It is suggested that, during early development, adaptive response to the prevailing physical conditions enhances survival in an estuarine environment.     

Phototactic responses of unfed walleye pollock,Theragra chalcogramma larvae: comparisons with other measures of condition

Synopsis The capability of unfed walleye pollock, Theragra chalcogramma, larvae to swim horizontally towards light was used as a sensitive, sublethal measure of larval condition. At 9°C, positive phototaxis and swimming ability of larvae was fully developed by 4–6 d after hatching, then decreased steadily until death by 12 d after hatching. This measure of larval condition corresponded closely with previously established benchmarks of larval condition, including first feeding, yolksac absorption, point of no return and death by starvation. The presence and timing of behavioral deficits associated with starvation, such as decreased ability to swim, feed and avoid predators, may have significant effects on the ability of larvae to vertically migrate, avoid predators and find and capture food.     

Feeding, morphological changes and allometric growth during starvation in miiuy croaker larvae

We investigated the effects of the timing of first feeding (larvae in F0, F1, F2, F3 and S were first fed on day 3, 4, 5, 6 days after hatching (DAH) and unfed, respectively) on feeding, morphological changes, survival and growth in miiuy croaker larvae at 24°C. The fed larvae initiated feeding on 3 DAH and reached point of no return (PNR) on 6 DAH. Larvae in F0 and F1 groups survived apparently better than F2 group at the end of the experiment on 36 DAH. High larval mortality occurred from 3 to 7 DAH in all feeding groups, accounting for 40% (F0, F1 and F2 groups) to 90% (F3 and S groups) of the total mortality. Larvae in F0 and F1 groups grew better than F2 group throughout the experiment. Eye diameter, body height, head height and mouth gape of the first feeding larvae were more sensitive to starvation than other morphometrics and could be used as indicators for evaluating their nutritional status. Results indicated that delayed first feeding over 1 day after yolk exhaustion could lead to poor larval survival and growth. To avoid starvation and obtain good growth in culturing, larvae feeding should be initiated within 1 day after yolk exhaustion at 24°C.     

Early ontogeny of Ancherythroculter nigrocauda and effects of delayed first feeding on larvae

Development of embryos and larvae in Ancherythroculter nigrocauda Yih et Woo (1964) and effects of delayed first feeding on larvae were observed after artificial fertilization. The fertilized eggs were incubated at an average temperature of 26.5°C (range: 25.7–27) and the larvae reared at temperatures ranging from 21.8 to 28°C. First cleavage was at 50 min, epiboly began at 7 h 5 min, heartbeat reached 72 per min at 24 h 40 min and hatching occurred at 43 h 15 min after insemination. Mean total length of newly hatched larvae was 4.04 ± 0.03 mm (n = 15). A one‐chambered gas bladder was observed at 70 h 50 min, two chambers occurred at 15 days, and scales appeared approximately 30 days after hatching. Larvae began to feed exogenously at day 4 post‐hatch at an average temperature of 24°C. Food deprivation resulted in a progressive atrophy of skeletal muscle fibres, deterioration of the larval digestive system and cessation of organ differentiation. Larval growth under food deprivation was significantly affected by the time of first exogenous feeding. Starved larvae began to shrink, with negative growth from day 6 post‐hatch. The point of no return (PNR) was reached at day 11 after hatching. Mortality of starved larvae increased sharply from day 12 after hatching.     

Impact of Daily Thermocycles on Hatching Rhythms,Larval Performance and Sex Differentiation of Zebrafish

In the wild, water temperature cycles daily: it warms up after sunrise, and cools rapidly after sunset. Surprisingly, the impact of such daily thermocycles during the early development of fish remains neglected. We investigated the influence of constant vs daily thermocycles in zebrafish, from embryo development to sexual differentiation, by applying four temperature regimens: two constant (24°C and 28°C) and two daily thermocycles: 28:24°C, TC (thermophase coinciding with daytime, and cryophase coinciding with night-time) and 24:28°C, CT (opposite to TC) in a 12:12 h light:dark cycle (LD). Embryo development was temperature-dependent but enhanced at 28°C and TC. Hatching rhythms were diurnal (around 4 h after lights on), but temperature- and cycle-sensitive, since hatching occurred sooner at 28°C (48 hours post fertilization; hpf) while it was delayed at 24°C (96 hpf). Under TC, hatching occurred at 72 hpf, while under CT hatching displayed two peaks (at 70 hpf and 94 hpf). In constant light (LL) or darkness (DD), hatching rhythms persisted with tau close to 24 h, suggesting a clock-controlled “gating” mechanism. Under 28°C or TC, larvae showed the best performance (high growth and survival, and low malformations). The sex ratio was strongly influenced by temperature, as the proportion of females was higher in CT and TC (79 and 83% respectively), contrasting with 28°C and 24°C, which led to more males (83 and 76%). Ovarian aromatase (cyp19a) expression in females was highest in TC and CT (6.5 and 4.6 fold higher than at 28°C, respectively); while anti-müllerian hormone (amh) expression in males increased in testis at 24°C (3.6 fold higher compared to TC) and particularly at 28°C (14.3 fold increase). Taken together, these findings highlight the key role of environmental cycles during early development, which shaped the daily rhythms in fish embryo and larvae, and ultimately influenced sex differentiation.     

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s^-1 m^-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s^-1 m^-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.     

Effects of the ecdysteroid agonists RH 5849 an RH 5992, alone and in combination with a juvenile hormone analogue, pyriproxyfen, on larvae ofSpodoptera exigua

Biological activity assays with RH 5849 and RH 5992 indicated that both compounds affected growth and development of last-instar larvae ofSpodoptera exigua (Hübner) (Lepidoptera: Noctuidae) in a dose-dependent manner. Within the first 24 h after treatment by continuously offering leaves dipped in a water solution of ≥50 mg/l RH 5849 and ≥0.5 mg/l RH 5992, symptoms of a prematurely induced larval moult and head capsule apolysis were visible. Intoxicated larvae died shortly afterwards, showing signs of unsuccessful ecdysis. LC₅₀-values of RH 5849 and RH 5992 for fifth-instarS. exigua larvae were 110 and 2.5 mg/l, respectively. Pyriproxyfen alone affected the larval stage and disturbed normal metamorphosis. One supernumerary larval instar occurred occasionally. LC₅₀-value for pyriproxyfen was 1.7 mg/l. Larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, continued to grow until they attained a size and weight about 2–3 times that of the controls. This growth was accompanied by at least one and sometimes two supernumerary moults. Concerning thein vivo imaginal wing disc growth and development, only in larvae treated with 10 and 50 mg/l RH 5849 or 0.5 mg/l RH 5992, tracheole migration was observed earlier than in the controls. When applying 300 mg/l RH 5849 or 3–7 mg/l RH 5992, the discs remained small and no signs of tracheole migration were observed. In larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, tracheole migration was not prematurely induced and a pupal cuticle was produced in the discs of larvae, undergoing a supernumerary moult. No clear signs of evagination were observed.     

Effects of salinity on growth and survival of African sharptooth catfish (clarias gariepinus) larvae

Growth and survival of replicate batches of African sharptooth catfish (Clarias gariepinus) larvae were monitored in 0, 2.5, 5.0, 7.5 and 10 ppt salinity. No significant differences in mortality or growth rate were evident between 0 and 5 ppt salinity. At 7.5 ppt mortality rate was higher and larval growth rate declined in comparison to the lower salinities. At 10 ppt all larvae died within 48 hours. The condition factor of the larvae similar between 0–2.5 ppt and displayed a declining trend between 2.5–7.5 ppt. Osmoconcentratkm of blood plasma of C. gariepinus in fresh water was 280 ± 20 mOsm/kg which is equivalent to 9.5 ppt salinity. It was concluded that 0–2.5 ppt is the optimal sclinity range for larval rearing and that short-term exposure to higher salinities (2.5–7.5 ppt) could be effective in the treatment of ectoparasitic diseases.     

Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night

Background

Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS.

Methods

Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30).

Results

A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions.

Conclusions

Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.     

Effects of prehatching salinity and initial larval biomass on survival and duration of development in the zoea 1 of the estuarine crab, Chasmagnathus granulata, under nutritional stress

The effects of individual larval biomass, and salinity experienced during embryogenesis (i.e., prehatching salinity) on starvation tolerance and growth of zoea 1 of the estuarine crab (Chasmagnathus granulata) were evaluated in laboratory experiments. Freshly hatched zoeae 1 were obtained from broods maintained at three salinities (15‰, 20‰ and 32‰), and cultured at 20‰ under different initial feeding periods and subsequent food deprivation (“point of reserve saturation” experiment: PRS) or under initial periods of food deprivation and subsequent feeding (point of no return experiment: PNR). Another group of larvae were used for determination of biomass (dry weight, carbon, and nitrogen) of zoea 1.Larval survival and duration of development depended on the length of feeding period: no larvae reached the second instar under complete starvation; survival was higher and duration of development shorter as the feeding period lengthened. After different initial feeding periods (PRS experiment), zoeae 1 that hatched from eggs incubated at the prehatching salinities of 15‰ and 20‰ showed higher survival and shorter duration of development than those at 32‰. Prehatching salinity also affected the amount of reserves accumulated during the first 2 days after hatching, with larvae from 15‰ and 20‰ showing the highest percentage of total accumulation of carbon and nitrogen. Initial larval biomass did not affect survival, but it had a slight effect on duration of development, with larger larvae (in terms of biomass) developing faster. After different initial starvation periods (PNR experiment), prehatching salinity did not affect survival, but it affected duration of development: larvae from 15‰ and 20‰ reached the second instar earlier. Variability in survival and duration of development was explained in part by among-brood variability in initial larval biomass: larvae with higher biomass showed higher survival and shorter duration of development. Thus, C. granulata, survival and duration of development under food stress depend on the interaction between environmental conditions experienced before and after hatching (pre- and posthatching factors, respectively).