Hatching Of Larvae Research Articles

Energetics and metabolism of yellowtail kingfish ( Seriola lalandi Valenciennes 1833) during embryogenesis

A study was undertaken to measure changes in oxygen consumption and metabolite concentration (ammonia, free amino acids, glucose, glycogen, ninhydrin positive substances and protein) in embryos of yellowtail kingfish ( Seriola lalandi) incubated at different temperatures (17, 19, 21 and 23 °C). The oxygen uptake at hatch and total oxygen consumed during embryogenesis was negatively correlated with temperature, and resulted in Q 10 values less than 1. This was attributed to the fact that embryos and first hatch larvae have been reported to be smaller at warmer incubation temperatures and therefore consumed less oxygen. Free amino acids were present in high concentrations immediately after spawning (188 ± 15.3 nmol ind − 1 ) and were dominated by the neutral amino acids alanine, glycine, isoleucine, leucine, serine, and valine. The free amino acid pool was rapidly depleted until hatch (20–40 nmol ind − 1 ), after which the pool was dominated by glycine, serine, valine and arginine/taurine (unresolved). The loss of positive buoyancy around the time of hatch was likely to be correlated with the decrease in free amino acid content during embryogenesis. The sequence of metabolic fuel use during embryogenesis is likely to be similar to that observed in other marine fish species with pelagic eggs, namely that carbohydrates, lipid and protein are of relatively minor importance compared to the catabolism of free amino acids for energy. Eggs incubated at 17, 19 and 21 °C had similar profiles of metabolite concentration during embryogenesis, however, eggs incubated at 23 °C were found to have a considerably different pattern of substrate utilisation, possibly indicative of abnormal physiological development at a temperature above that which is routinely encountered in the wild.

Life cycle of the coleopter Bruchidius raddianae and the seed predation of the Acacia tortilis Subsp. raddiana in Tunisia

Seeds of Acacia tortilis (Forsskal) Hayne ssp. raddiana (Save) Brenan, a savannah tree of great potential for forestry and an excellent browse for game and livestock, is heavily infested by the bruchid beetle Bruchidius raddianae Anton & Delobel. The development from egg to beetle, and the various development stages were investigated using Scanning Electron Microscopy (SEM). The adult B. raddianae lays eggs on the green pod in the autumn. The first instar larva hatches from five to seven weeks and develops outside the host seed. From the second instar onwards development took place inside the host seed. Pupation takes about three weeks, late in the summer. The beetle of B. raddianae is univoltine and the newly emerged adult makes an exit hole to leave the seed. During the development from first instar lava to imago, all embryonic tissue is destroyed. This results in a weakness of its soil seed stock, which reduces the possibilities of natural regeneration of the species. To cite this article: S. Derbel et al., C. R. Biologies 330 (2007).

Egg hatching and survival time of soil-dwelling insect larvae: A partial differential equation model and experimental validation

Insect herbivores that have soil-dwelling larval stages usually lay eggs directly or indirectly into the soil. Following egg hatch, emergent larvae must locate host plant roots to avoid starvation and this represents the most vulnerable part of the life cycle. We present a model for this aspect of the life cycle, specifically modelling the egg development rate and survival time of the clover root weevil, Sitona lepidus. The model is based on a partial differential equation, developed from age-structure models that are widely used in ecology. The model incorporates stochastic random variation caused by environmental fluctuation and genetic variation in a population, and treats chronological time and biological age as two independent variables. The average developmental rate and the impact of randomness are described by a first-order and a second-order derivative term, respectively. The significance of this model is that it can combine two biological events (egg development and larval survival time) into a single functional event, a potentially important feature for soil-dwelling insects because their concealed habitat does not permit all biological events to be observed. The model was tested against experimental observations of egg development and larval survival time under different soil conditions, firstly by considering egg development and larval survival time as independent biological events and secondly by combining both into a single functional event. Model simulations and experimental observations were in close agreement in all cases. To further test whether the model could be applied to other insect taxa and incorporate more than two biological events, we compared model simulations with published experimental results for the cereal leaf beetle ( Oulema duftschmidi). Simulations of egg hatching and the larval development through several instars compared favourably with all experimental observations, demonstrating that the model has multiple applications.

Influence of climate variability on whitefish (Coregonus lavaretus) year-class strength in a deep, warm monomictic lake

The year-class strength (YCS) of Blaufelchen (Coregonus lavaretus) in deep Upper Lake Constance was analysed for a 52-year period, from 1947 to 1998. Despite strong anthropogenic influences on the species' population dynamics due to cultural eutrophication and oligotrophication, intense fishing, and large-scale stocking, the influence of climate variability associated with the North Atlantic Oscillation (NAO) is apparent in the data set. This influence is significant although large-scale stocking of cold-bred larvae was performed to avoid a mismatch of larvae with their food. The importance of stocking on YCS, however, is unclear and was only detectable when analysing a subset of the data. In addition to climate variability a yet unidentified factor related to zooplankton suitability as food for fish larvae, and density-dependent mortality probably related to cannibalism do significantly influence YCS. The NAO seemed to influence YCS twofold, through temperature effects on egg development time and on larval growth rate. The first of these two mechanisms is related to the NAO via a time lag of 1 year due to the specific mixing dynamics of warm monomictic Lake Constance. Hence, a warm winter in the year before spawning results in earlier hatching of larvae, that is, hatching is decoupled from the actual meteorological conditions. This should make the larvae very prone to mismatch the dynamics of their food. However, we found no evidence for such a mismatch in this 52-year data set.

The efficiency of extracts of Dahlstedtia pentaphylla (Leguminosae, Papilionoidae, Millettiedae) on Boophilus microplus (Canestrini, 1887) in artificially infested bovines

Tests were conducted to assess the efficiency of the roots of Dahlstedtia pentaphylla (Taub.) Burk. (Leguminosae, Papilionoideae, Millettiae) plant against infestations of Boophilus microplus (Canestrini, 1887). These tests were performed on 30 bovine animals in the Paraíba Valley, State of São Paulo, Brazil, divided into three groups (control, extract diluted at 1:10 mL and extract diluted at 1:20 mL), after artificial infestation with some 4000 larvae/animal on days −21, −14, −7, −1, 0, 7 and 14. The extract of D. pentaphylla was obtained by dehydration, spraying and extraction in absolute ethanol, at a proportion of one part of root powder to three parts of ethanol, this being taken as standard (100%). This standard extract was then diluted in water at one part of extract to 10 and 20, for spraying on the bovines. The best result obtained (an efficiency rate of 76.10%) was seen 3 days after the application of the extract at a concentration of 1:10 mL. The extract showed no effect in inhibition of the laying or hatching of larvae on engorged females, these being collected from the bovines after treatment, and kept in the laboratory.

Phenotypic links in complex life cycles: conclusions from studies with decapod crustaceans

I review studies on decapod crustaceans to draw conclusions about the importance of effects of past environmental conditions on development, phenotype, performance, and survival in animals. I consider 3 critical points of the life cycle: the allocation of reserves into eggs, the hatching of larvae, and metamorphosis from the larval to the juvenile phase. Biomass allocated to eggs varies among females as a response to changes in environmental conditions. These variations are propagated to the larval stages, influencing the biomass at hatching, subsequent larval developmental pathways, and survival during periods of limited starvation. Suboptimal conditions experienced by embryos increase the loss of mass during embryogenesis; size or biomass of the juvenile is either positively or negatively correlated with initial biomass. Positive correlations may be the normal pattern; negative correlations occur when individuals hatched with low initial biomass follow developmental pathways that lead to increased biomass at metamorphosis. In estuarine crabs, salinity experienced by embryos leads to salinity acclimation in early larval stages. Phenotypic links originate as transgenerational effects that propagate to the juvenile stages. There are least 3 types of effects: disruption of physiological processes; direct adaptive responses; and indirect consequences of adaptive mechanisms. All types appear within a species; they are produced as a response to a single environmental factor. Variability in phenotype remains latent and is expressed in terms of survival according to the environmental conditions experienced by a particular stage. The fate of individuals is thus affected by interactions between their immediate developmental processes and their environmental history.

Toxicity of tetrabromobisphenol A (TBBPA) in zebrafish (Danio rerio) in a partial life-cycle test

Toxicological effects of the widely used flame retardant, tetrabromobisphenol A (TBBPA) were assessed in a partial life-cycle test with zebrafish (Danio rerio). Exposure of adult fish during 30 days to water-borne TBBPA in nominal concentrations ranging from 0 (control) to 1.5 microM was followed by exposure of the offspring in early life stages up to 47 days posthatching (dph) to the same concentrations. Adults exposed to 3 and 6 microM showed severe disorientation and lethargy shortly after beginning of exposure and were euthanized. Because semistatic exposure resulted in fluctuating water concentrations, pooled fish samples were chemically analyzed for internal dose assessment. Egg production was decreased in fish exposed to TBBPA concentrations of 0.047 microM and higher, and a critical effect level of 7.2 microg/g lipid with a lower 5% confidence limit of 3.9 microg/g lipid for 50% decreased egg production was calculated. Histology of adult ovaries indicated a relative increase of premature oocytes in two surviving females exposed to 1.5 microM. Hatching of TBBPA-exposed larvae was decreased except in animals exposed to 0.375 microM. In the highest exposure concentration, early posthatching mortality was high (81%) in larvae and the surviving juveniles showed a significant predominance of the female phenotype. Exposure of eggs from control parents up to 6 microM TBBPA resulted in increasing malformation and pericardial fluid accumulation from 1.5 microM; at higher concentrations, all embryos failed to hatch. The presented results indicate decreased reproductive success in zebrafish at environmentally relevant TBBPA concentrations.

Effect of Air Humidity on the Egg Viability of Predatory Mites (Acari: Phytoseiidae, Stigmaeidae) Common on Rubber Trees in Brazil

Rubber pest mites, Calacarus heveae and Tenuipalpus heveae, reach economic damage levels at the end of the rainy season and the beginning of the dry season in Brazil. Therefore, low humidity adaptation might be an important characteristic for predatory mites to successfully control pest organisms. This study determined the effect of the relative humidity (RH) levels of 30-100% on the hatching of larvae of Amblyseius acalyphus, Euseius citrifolius, Iphiseiodes zuluagai, Metaseiulus camelliae, Agistemus floridanus and Zetzellia malvinae at 25 +/- 0.5 degrees C. These predatory mites are common on rubber trees in the state of São Paulo and might be used for introduction in the major rubber tree production regions in the state of Mato Grosso. At 70% RH or higher, viability was 70% or higher for all species, indicating that their performance might be higher during the rainy season than during the dry season. Eggs of E. citrifolius and M. camelliae presented higher viability at the lower relative humidity levels than those of other species, indicating that these species might have higher chance to persist in the dry season. It is suggested that M. camelliae should be further evaluated for introduction in the state of Mato Grosso, considering that this mite is not yet present in that area.

Lepidosaphes ussuriensis

<i>Lepidosaphes ussuriensis</i>

Maternal and paternal influences on early life history traits and processes of Baltic cod Gadus morhua

Embryo survival, larval standard length, yolk-sac area, yolk utilization and resistance to starvation were significantly influenced by the female parent and the interaction between both parents of Baltic Sea cod Gadus morhua in a gamete factorial cross of 3 females and 5 males in all possible combinations. The proportion of variance in embryonic survivorship that was due to maternity during incubation was significant during the first 4 d, but was insignificant during the 5 to 9 d interval. During the 5 to 9 d interval, the male–female interaction was significant. Standard lengths at hatch and 5 d post hatch and specific growth rate of unfed yolk-sac larvae were strongly influenced by the female. Equivalent amounts of variation in larval resistance to starvation were explained by maternity and bi-parental interaction. Paternity alone did not explain a significant amount of variation for the traits or processes examined. The bi-parental interactions reported demonstrate a female’s choice of mate could significantly influence the early life survivorship of Baltic cod offspring.

The use of tannic acid to remove adhesiveness from pikeperch, Sander lucioperca, eggs

The studies conducted in 2003–2004 focused on the possibilities of applying a tannic solution to remove adhesiveness from pikeperch eggs. Spawners were caught in Lake Pątnowskie (central Poland) and then transported to the Goslawice Fish Farm. After initial selection, the fish were weighed, measured and stimulated with human chorionic gonadotropin. Gametes were obtained 5 days after the first injection. The weight and diameter of the eggs, and the commercial fecundity of individual females were determined. The eggs were fertilized with the dry method. After the addition of water, the eggs were mixed for 4 min, and then divided into 20 g portions. After determining the number of eggs in the various portions, the adhesiveness removal procedure was performed. Three concentrations of tannic acid solution (500, 1000, 1500 mg L−1) and three exposure times (0.5, 2, 5 min) were applied. The eggs were incubated in Weiss jars. The studies indicated that both the solution concentration and the exposure time significantly (P<0.05) impacted pikeperch egg hardening, the degree of adhesive removal and embryo survival. The tannic acid solution concentration of ≤500 mg L−1 applied for 0.5–2 min was not effective; the eggs clumped and it was impossible to separate them even with intensive mixing. Better results were obtained using higher tannic acid concentrations and/or by lengthening exposure time. The adhesiveness of pikeperch eggs disappeared completely after 5 min exposure to tannic acid solution concentrations of 500–1500 mg L−1 or after 2 min exposure to solution concentrations of 1000–1500 mg L−1. In these variants, the embryo survival rate to the eyed-egg stage was 78.0–84.0% (2003) and 82.3–84.7% (2004). However, high tannic acid concentration had a negative impact on the pikeperch larvae hatching. The greatest decrease in survival rate was observed in groups exposed to a tannic acid solution of 1500 mg L−1 for 2 and 5 min periods. Thus, the optimum method for removing pikeperch egg adhesiveness was to apply a solution of tannic acid at a concentration of 500 mg L−1 for 5 min or 1000 mg L−1 for 2–5 min.

Effects of incubation temperature on development and yolk sac conversion efficiencies of spotted wolffish (Anarhichas minor Olafsen) embryos until hatch

Two egg batches of spotted wolffish, Anarhichas minor Olafsen, were incubated at 4, 6 and 8°C. Embryo samples were fixed and compared on each 100th daydegree until hatching (up to 1000 daydegrees). Embryos, yolk sacs and chorions were dissected and the sizes, wet and dry weights were recorded separately. Comparisons of gross morphologies and measured parameters showed increasing and generally significant differences with time between the incubation temperatures. Lower temperatures produced longer and more differentiated larvae at hatch with a smaller yolk sac. Even though some unexpected deviations were registered among batches and experimental groups, it was clear that temperature affected embryo survival and time of hatching. Overall survival was best at 6°C, in agreement with results from earlier studies. Yolk conversion efficiencies measured around the hatching point were generally high, ranging from 60% to 78%, varied between the two batches and probably reflected the developmental variations between embryos and larvae at the respective ages (daydegrees). The hatching process was apparently an energy-demanding period; yolk conversion efficiencies of unhatched embryos of similar age at each temperature were always higher. Temperature is one environmental factor that can be manipulated in hatcheries to induce hatching of viable larvae at an optimal stage of differentiation with respect to first-feeding success and early survival.

Effect on Breeding Performance and Egg Quality of Clarias batrachus (Linn.) at Various Doses of Ovatide During Spawning Induction

An experiment was conducted to evaluate Ovatide doses (0.5, 1.0, 1.5 and 2.0 ml·kg body weight of female) on breeding performance and egg quality of Clarias batrachus. The breeding performance was judged on the basis of the total weight of stripped eggs, spawning fecundity and stripping response. To judge the egg quality, the per cent fertilization, hatching, deformity and normal larvae were considered. The results indicated that the total weight of stripped eggs and spawning fecundity were the highest (p &lt; 0.05) when females were injected 1 ml of Ovatide per kg body weight (BW) compared to those injected with other dose levels. The lowest stripping response was observed with injection of 0.5 ml Ovatide per kg BW. There was difficulty in stripping at 0.5, 1.5 and 2.0 ml doses, but at 1 ml dose, it was smooth. At the 1 ml dose, the percentages of fertilization and hatching were 83 and 71 % respectively, which were the highest (p &lt; 0.05) among all treatments. Increasing Ovatide doses above 1 ml led to over ripening of ova, which resulted in increased per cent deformed larvae. More normal larvae were produced from the females when injected the 1 ml dose. One ml of Ovatide per kg body weight was found optimum for best breeding performance and egg quality in C. batrachus.

The Molecular Basis of Odor Coding in the Drosophila Larva

We have analyzed the molecular basis of odor coding in the Drosophila larva. A subset of Or genes is found to be expressed in larval olfactory receptor neurons (ORNs). Using an in vivo expression system and electrophysiology, we demonstrate that these genes encode functional odor receptors and determine their response spectra with 27 odors. The receptors vary in their breadth of tuning, exhibit both excitation and inhibition, and show different onset and termination kinetics. An individual receptor appears to transmit signals via a single ORN to a single glomerulus in the larval antennal lobe. We provide a spatial map of odor information in the larval brain and find that ORNs with related functional specificity map to related spatial positions. The results show how one family of receptors underlies odor coding in two markedly different olfactory systems; they also provide a molecular mechanism to explain longstanding observations of larval odor discrimination.

Influência da salinidade na incubação de ovos do robalo-peva (Centropomus parallelus Poey, 1860)

The robalo-peva is an estuarine-dependent species that has great potential for aquaculture. Thus, it is very important to determine the effect of salinity on its early life history. The present study evaluated the influence of different salinity levels 15, 20, 25, 30 and 35 on egg hatching and quality of larvae. Experimental units were beakers with 800 mL of water at 26ºC of temperature. Parameters used in statistical analysis were rates of hatching and of deformed larvae by means of the &chi;2 non-parametric test (&alpha;=0.05). There was a significant dependence between salinity and the evaluated parameters. The best results in hatching rate were obtained at 35 and 30, probably due to the positive effect on eggs flotation. Deformed larvae were observed (18 to 43%) in all salinity levels. Taking into account both parameters, hatching and deformed larvae, the range 30 to 35 could be recommended as the most appropriate for incubation of robalo-peva eggs

Field evaluation of anthelmintic drug sensitivity using in vitro egg hatch and larval motility assays with Necator americanus recovered from human clinical isolates

A field-applicable assay for testing anthelmintic sensitivity is required to monitor for anthelmintic resistance. We undertook a study to evaluate the ability of three in vitro assay systems to define drug sensitivity of clinical isolates of the human hookworm parasite Necator americanus recovered from children resident in a village in Madang Province, Papua New Guinea. The assays entailed observation of drug effects on egg hatch (EHA), larval development (LDA), and motility of infective stage larvae (LMA). The egg hatch assay proved the best method for assessing the response to benzimidazole anthelmintics, while the larval motility assay was suitable for assessing the response to ivermectin. The performance of the larval development assay was unsatisfactory on account of interference caused by contaminating bacteria. A simple protocol was developed whereby stool samples were subdivided and used for immediate egg recovery, as well as for faecal culture, in order to provide eggs and infective larvae, respectively, for use in the egg hatch assay and larval motility assay systems. While the assays proved effective in quantifying drug sensitivity in larvae of the drug-susceptible hookworms examined in this study, their ability to indicate drug resistance in larval or adult hookworms remains to be determined.

Effects of temperature on development of vedalia beetle, Rodolia cardinalis (Mulsant)

Abstract The effect of temperature on the development of the vedalia beetle, Rodolia cardinalis (Mulsant) (Coleoptera: Coccinellidae), fed Icerya purchasi Maskell (Homoptera: Margarodidae) under controlled laboratory conditions was studied. Adults exposed to temperatures of 25, 28, 31, 34, and 37 °C for 72 h showed 95–100% survival, however egg production was significantly reduced at 34 and 37 °C. In addition, eggs maintained at 34 °C showed reduced hatch and survival of larvae, and eggs held at 37 °C failed to hatch. The duration of each developmental stage and survival of each stage were measured at 10, 14, 18, 22, and 25 °C. There was no egg eclosion at 10 °C. The developmental time from egg to adult emergence decreased from 79 to 18 days for temperatures from 14 to 25 °C. The sex ratio was unaffected by these temperatures. The lower developmental temperature threshold of R. cardinalis was estimated to be 10.8 °C and the degree–day accumulation was calculated as 279 for development from egg to adult eclosion. These results will guide further research designed to optimize management of vedalia populations in the San Joaquin Valley of California.

Ontogeny of corticotropin-releasing factor and of hypothalamic–pituitary–interrenal axis responsiveness to stress in tilapia ( Oreochromis mossambicus; Teleostei)

The ontogeny of the corticotropin-releasing factor (CRF) system and of the ability of the hypothalamic–pituitary–interrenal (HPI) axis to respond to stressors (capture or confinement), or to cortisol treatment was investigated in tilapia ( Oreochromis mossambicus). In 2 days post hatching (dph) larvae, the first developmental stage used for immunohistochemistry, CRF-immunoreactivity (ir) was observed in the nucleus preopticus (npo), and in two hypothalamic nuclei (nlt and nrl). In this stage, CRF- and AVT-ir was found in the neural part of the pituitary, and endocrine cells in the pars distalis and pars intermedia contained POMC-derived peptides. In the ventral telencephalon, CRF-ir cells were first observed 5 dph, whereas projections from these cells into the anterior part of the latero-dorsal telencephalon (Dla) from 7 dph onwards. CRF, ACTH, α-MSH, and cortisol were quantified by radioimmunoassays in homogenates of the anterior-cranial region of the larvae containing brain, pituitary, and headkidneys. CRF contents increased from 43 ± 3 to 1070 ± 70 pg/larvae between 5 and 110 dph. Larvae of age 5, 12, 24, and 42 dph were captured sequentially from a group. All life stages were able to rapidly increase their cortisol content in response to this stressor (ANOVA: P < 0.001). Overall, the developmental stage affected cortisol content (ANOVA: P < 0.001), but developmental stage did not influence the cortisol reaction to stress (ANOVA: P > 0.162). Whole brain CRF content did not change during the 20 min stress period and the relationship between CRF-producing neurons and the initial HPI stress response in early life stages remains to be established. Cortisol feeding of 18 and 29 dph larvae for periods ranging from 2 to 24 days resulted in elevations of the CRF content ( P < 0.003) in comparison to controls. In 18 dph larvae cortisol feeding abolished the cortisol response to capture stress as observed in control fed larvae ( P < 0.008). We propose that cortisol induced upregulation of CRF takes place in the telencephalon and is restricted to a time period during larval development, characterised by the absence of glucocortoid receptor (GR) expression in the telencephalic Dm region in these larvae. Finally, the stress response to 24 h confinement was compared between saltwater adapted and freshwater adapted juveniles (age 77 dph). Confinement stress (24 h) affected cortisol and CRF content (ANOVA: P < 0.001, P < 0.008, respectively), but not ACTH content. Interactions were observed between salinity and confinement regarding cortisol and α-MSH contents (ANOVA: P < 0.02), but not regarding CRF and ACTH contents. The increase in cortisol levels induced by confinement was remarkably high in freshwater adapted larvae (five times higher than in saltwater adapted larvae). Regarding the cortisol response it is concluded that during and after the period of mouth breeding tilapia larvae respond to capture stress in a similar fashion (onset and height) as adults. Previously, we reported that the initial plasma cortisol response to capture stress in adult tilapia occurred independently from changes in plasma ACTH levels. The current finding that also brain CRF contents do not alter during the initial cortisol response in larvae further indicates that the initial cortisol response in this species may be regulated independently from CRF and ACTH.

Effects of storage and incubation temperature on the viability of eggs, embryos and larvae in two strains of an African catfish, Heterobranchus longifilis (Siluriformes, Clariidae)

Two experiments, dealing with short-term storage of ova and thermal conditions to optimize gamete and eggs management in hatcheries of the African catfish, Heterobranchus longifilis, were carried out. In the first experiment, ova collected by stripping from two strains of H. longifilis were stored for intervals up to 8 h at two temperature regimes: in a domestic refrigerator (3–5°C) and at ambient room temperature (20.5–22°C). In the second experiment, eggs were incubated from fertilization to hatching at different experimental temperatures (21, 25, 29, 32 and 35°C) to determine the effects of temperature on the kinetics of white egg appearance, hatching times and hatching quality. Gamete storage at warmer temperatures significantly prolonged viability irrespective of the strain used. In fact, the hatching rate for ova stored at 20.5–22 and 3–5°C for 5 h ranged between 75.2–79.3% and 6.5–9.4% respectively. Loss of viability was most noticeable after 6 h storage at ambient room temperature. Post-storage viability significantly declined after 2 h exposure to the domestic refrigerator temperature. No hatching of normal larvae took place after 8 h post-storage time. Results from the second experiment showed that time to maximum whitening of eggs was both strain- and temperature-dependent. The time to maximum mortality of eggs was shorter in the Layo strain (LS) than in the Noun strain (NS), regardless of incubation temperature. The appearance of white eggs was shorter with increasing incubation temperatures. Hatching times decreased with increasing temperature, regardless of strain. Hatching took place from 21 to 27 h and 19 to 24 h after fertilization at temperature of 29°C, respectively, for NS and LS. The length of the hatching period was remarkably shorter for LS than NS at any tested incubation temperature, except 35°C. No hatching took place at 21°C. The highest proportion of normal larvae occurred at 25 and 29°C, respectively, for NS and LS. Hatching rate was highest at 25 and 29°C, respectively, for NS and LS. There was a significantly higher proportion of deformed larvae at 35°C regardless of the strain.

Hormonal coordination of molting and female reproduction by ecdysteroids in the mole crab Emerita asiatica (Milne Edwards)

The measurement of hemolymph ecdysteroids using radioimmunoassay (RIA) indicates a biphasic increase during intermolt and premolt stages of the mole crab Emerita asiatica. The gradual rise during intermolt stage corresponds to vitellogenic activities in the ovary; whereas a distinctive premolt peak is characteristic of molting crustaceans. Injection experiments with 20-hydroxyecdysone (20E) during different molt cycle stages revealed the onset of precocious premolt changes, as determined by the epidermal retraction and setal development. Injection of 20E augmented protein synthesis in the ovary, hepatopancreas and integumentary tissues. Quantification of ecdysteroids in different developmental stages of ovary also indicated a progressive increase of ovarian ecdysteroids. Interestingly, the ovarian ecdysteroids after reaching a peak at C 3 stage, start declining drastically to reach the lowest level at D 3–4 stage. This decline in the ovarian ecdysteroids is inversely related to rising hemolymph ecdysteroids during these active premolt stages. The hatching of the embryos, attached to the pleopods of the ovigerous females also occurs under a high titer of hemolymph ecdysteroids. In support, 20E injection at C 3 stage crabs indicated a significant reduction in time duration of pleopodal embryonic development leading to hatching of zoea larvae. Understandably, the augmented hemolymph ecdysteroid titer helps in the synchronization of embryo hatching and the premolt changes, as occurring under the normal premolt conditions.