Early Postlarvae Research Articles

Limpet larvae (Patella aspera Röding, 1798), obtained by gonad dissection and fecundation in vitro, settled and metamorphosed on crustose coralline algae

AbstractThe limpet Patella aspera Röding, 1798, is a native species from the Macaronesian region whose fishing is regulated. The early life of limpets, including the settlement process, is poorly known thus far. The current study evaluated different substrates to induce settlement in P. aspera, including microalgae strains (Halamphora coffeaeformis, Navicula incerta and Pavlova sp.) and crustose coralline algae (CCA) obtained from limpet shells. The results showed that gametes obtained by dissection and matured artificially using alkalinized seawater baths can produce viable larvae able to metamorphose to juveniles. Feeding was not required during larval development, suggesting lecithotrophy. Early postlarvae were identified by the shedding of the velum, and juveniles were identified by teleoconch and active grazing behaviour. The presence of CCA shortened the timing for settlement and increased the ratio of juveniles. The type and abundance of CCA can influence settlement success. Moreover, the results suggested that settlement and metamorphosis in true limpets (Patellogastropoda) might be triggered by a two-step mechanism, i.e. a first cue influencing the shift between swimming and crawling activity and a second cue determining settlement and metamorphosis to early postlarvae and juveniles.

Insights into the microbiota of larval and postlarval Pacific white shrimp (Penaeus vannamei) along early developmental stages: a case in pond level.

Increasing studies have revealed strong links among gut microbiota, health status, and shrimp development, but they mainly focus on the microbiota of Pacific white shrimp, Penaeus vannamei, during life stages from juveniles to adults. Little is known about shrimp microbiota dynamics at early developmental stages. In this study, with an aim to profile shrimp microbiota and its dynamics at stages nauplius, zoea, mysis, and early postlarva, we conducted a survey for the successful breeding processes in a commercial hatchery in China, sampled 33 samples including larval/postlarval shrimp, suspended substance in rearing water (SSRW), and nutrition supplements (i.e., algae and brine shrimp larvae) at stages N5, Z2, M2, and P2. The associated bacterial communities were sequenced and comparatively analyzed using high-throughput sequencing of bacterial 16S rRNA genes. Our case study results showed that bacterial community structures and compositions were strikingly different at stages N5, Z2, and P2, indicating the shift of microbiota at the three stages. Many taxa within Gamma-, Alphaproteobacteria, and Flavobacteriia classes were observed to be stage-specifically abundant and identified as taxonomic biomarkers potentially used to differentiate among shrimp at different early developmental stages. Summing up, these results shed light on larval/postlarval microbiota and its dynamics at different early developmental stages, highlighting the potential roles of shrimp development in microbiota formation and shifting.

Fine-scale succession patterns and assembly mechanisms of bacterial community of Litopenaeus vannamei larvae across the developmental cycle

BackgroundMicrobiome assembly in early life may have a long-term impact on host health. Larval nursery is a crucial period that determines the success in culture of Litopenaeus vannamei, the most productive shrimp species in world aquaculture industry. However, the succession patterns and assembly mechanisms of larval shrimp bacterial community still lack characterization at a fine temporal scale. Here, using a high-frequency sampling strategy and 16S rRNA gene amplicon sequencing, we investigated dynamics of larval shrimp bacterial community and its relationship with bacterioplankton in the rearing water across the whole developmental cycle in a realistic aquaculture practice.ResultsAlpha-diversity of larval shrimp bacteria showed a U-shaped pattern across the developmental cycle with the stages zoea and mysis as the valley. Correspondingly, the compositions of dominant bacterial taxa at the stages nauplius and early postlarvae were more complex than other stages. Remarkably, Rhodobacteraceae maintained the overwhelming dominance after the mouth opening of larvae (zoea I~early postlarvae). The taxonomic and phylogenetic compositions of larval bacterial community both showed stage-dependent patterns with higher rate of taxonomic turnover, suggesting that taxonomic turnover was mainly driven by temporal switching among closely related taxa (such as Rhodobacteraceae taxa). The assembly of larval bacteria was overall governed by neutral processes (dispersal among individuals and ecological drift) at all the stages, but bacterioplankton also had certain contribution during three sub-stages of zoea, when larval and water bacterial communities were most associated. Furthermore, the positive host selection for Rhodobacteraceae taxa from the rearing water during the zoea stage and its persistent dominance and large predicted contribution to metabolic potentials of organic matters at post-mouth opening stages suggest a crucial role of this family in larval microbiome and thus a potential source of probiotic candidates for shrimp larval nursery.ConclusionsOur results reveal pronounced succession patterns and dynamic assembly processes of larval shrimp bacterial communities during the developmental cycle, highlighting the importance of the mouth opening stage from the perspective of microbial ecology. We also suggest the possibility and potential timing in microbial management of the rearing water for achieving the beneficial larval microbiota in the nursery practice.EV4FFVE7Wr7jezsPpZE3f6Video

Scanning Electron Microscopic Aids for Identification of Larval and Post-Larval Bivalves

The identification of bivalve larvae and early postlarvae in plankton and benthic samples has long been a challenge, hampering both basic and applied research efforts in marine, estuarine, and freshwater environments. The usefulness of published optical micrographs of the early life-history stages of bivalves is limited because of the great morphological similarity of the imaged articulated shells, particularly at the early (straight-hinge) developmental stages. While a number of techniques have been refined in recent years and show promise for use in routine identifications of larval and post-larval bivalves (e.g., single-step nested multiplex polymerase chain reaction; in situ hybridization protocols through color coding with taxon-specific, dye-labeled DNA probes; coupled fluorescence in situ hybridization and cell sorting; and image analysis techniques using species-specific shell birefringence patterns under polarized light), no adequate comprehensive reference source exists that accurately depicts the morphology and morphometry of the shells of larval and post-larval stages of target bivalve species in a consistent format to assist in identification of such stages. To this end, scanning electron micrograph (SEM) sequences are presented of the disarticulated shell valves of laboratory-reared larval and post-larval stages of 56 species of bivalve molluscs from a wide spectrum of marine, estuarine, and freshwater habitats. Emphasis is placed on the usefulness of the morphology and morphometrics of consistently-oriented, disarticulated shell valves and associated hinge structures in discriminating the early life-history stages of these various bivalve species. Although the scanning electron micrograph sequences presented accurately depict the gross morphologies/ morphometrics and hinge structures of the disarticulated shell valves of the larvae and/or postlarvae of the 56 species of bivalves, it is important to emphasize that a scanning electron microscope is not necessary to observe even fine hinge structures associated with the early ontogenetic stages of these species. Such structures are readily visible using a wide range of optical compound microscopes equipped with high-intensity reflected light sources, although the disarticulated shell valves must be viewed in several planes of focus to discern the often subtle details seen clearly in the scanning electron micrographs. These morphological characters provide researchers with invaluable aids for the routine identification of the early life-history stages of these species isolated from plankton and benthic samples.

Psychrobacter sp. 17-1 enhances growth and survival in early postlarvae of white shrimp, Penaeus vannamei Boone, 1931 (Decapoda, Penaeidae)

The effects of Psychrobacter sp., isolated from the gut of shrimp Penaeus vannamei Boone, 1931, on growth, digestive enzyme activities, total protein content, osmotic stress resistance, immunity and disease resistance of postlarvae were investigated. For enzymatic activities assays whole postlarvae were homogenized. Shrimp subjected to Psychrobacter sp. treatment showed higher weight (40%) and length (5.6%) than that observed in untreated animals. Compared to the untreated control group, levels of protease and amylase activities in postlarvae, were higher in the probiotic group. Postlarvae treated with Psychrobacter sp. showed significantly increase in the survival compared to the untreated ones after osmotic stress. Nitric oxide metabolite levels and the enzymatic activities of phenoloxidase, superoxide dismutase and peroxidase from treated postlarvae were significantly higher than untreated postlarvae. Increased survival was also found after challenge with Aeromonas sp. This is the first study that demonstrates the probiotic effect of Psychrobacter sp. in P. vannamei postlarvae.

Early benthic juvenile Parvulastra exigua (Asteroidea) are tolerant to extreme acidification and warming in its intertidal habitat

Habitat warming and acidification experienced by intertidal invertebrates are potentially detrimental to sensitive early post-larvae of benthic marine invertebrates. To determine the potential impact of acidification and warming on a conspicuous component of the temperate intertidal fauna of the southern hemisphere, the response of newly metamorphosed juvenile (ca. 450μm diameter) sea stars (Parvulastra exigua) to increased acidification and temperature was investigated with respect to conditions recorded in the habitat (−0.4–0.6pH units, +2-4°C), in all combinations of stressors. In situ monitoring was used to generate data on environmental conditions. The pHNIST of the tide pools varied from 7.54 (pCO2 2045μatm) at predawn to 8.91 (pCO2 28μatm) in the afternoon and temperature varied from 10°C at night to 24°C during the day, conditions that fluctuated from baseline sea surface conditions of pH8.2 and 16°C. P. exigua was used as a model tolerant intertidal species to generate insights into stress tolerance of the early benthic life stage. After a 4-week incubation in experimental conditions, negative effects on juvenile development and growth were only observed at pHNIST 7.2 (−1.0units/pCO2 4430–4601μatm; Ωcal 0.6, Ωar 0.4). Our results indicate that juvenile P. exigua is physiologically acclimatised to tolerate extreme conditions indicating that it may be robust to near future (ca. 2100) change in ocean conditions. Although it is difficult to know how tide pools will change in the future, pulses of the deleterious level of acidification (pHNIST 7.2) may occur in the intertidal in future night time low tides.

Application of Spirulina for Feeding Larvae of Green Tiger Shrimp, Peneaus semisulcatus

This experiment was carried out in Bandargah Station in Bushehr province. Peneaus semisulcatus larvae were fed on Spirulina platensis as supplementation microalgae. In order to use Spirulina platensis in this study, we have to produce biomass and dry production of this microalga. Determination of length and survival rate of Peneaus semisulcatus larvae was carried out as the objective of the study. Treatments including Z plus (as a supplementation without spirulina), M.C.F (as an imported enriched spirulina), the powder combination of Spirulina platensis with Z plus and Spirulina platensis as live food were compared to Cheatocerus microalgae as a control. The experiment was carried out from nauplii stage to early post larvae. The results of the experiment indicated that the powder combination of Spirulina platensis with Z plus treatment has the most survival rate (76.5%). The maximum of length (4.3 mm) observed in control (Cheatocerus spp). The maximum mortality was observed in zoa stage in Spirulina microalgae treatment, because the spiral filamentous of Spirulina sp. was large.

Effect of three bacterial isolates from a commercial hatchery on early red abalone (Haliotis rufescens) postlarvae

Three bacterial strains, GHrC11, GHrC13 and GHrC15, were isolated from an abalone postlarval culture system in a commercial farm at Baja California, Mexico. The strains were phenotypically characterized and sequenced (16S rDNA). Strain GHrC11 was a Gram-positive coccobacillum, while strains GHrC13 and GHrC15 were Gram-negative bacilli. Strain GHrC11 was identified as Exiguobacterium sp. The strains GHrC13 and GHrC15 were identified as Vibrio splendidus. The effects of these strains for the development of early abalone postlarvae (2 days old) were evaluated following a completely randomized design with three replicates using 5-mL-volume Petri dishes as experimental units. The experiment considered two different bacterial concentrations of each strain (103 and 105 cells ml−1) and two controls (with and without the benthic diatom Navicula incerta). After 10 days of experimentation, the highest mortality (90 ± 5.8 %) and the lowest growth rate (4.1 ± 0.1 μm day−1) were recorded for the strain GHrC11. In contrast, the lower mortality (16.7 ± 3.3 %) and the highest growth rate (11.2 ± 0.9 μm day−1) corresponded to the control fed N. incerta. Our results suggest that pathogenic effects of these bacterial strains were stronger than any potential benefits derived from the ingestion of bacteria by early abalone postlarvae. In conclusion, the most pathogenic strain was GHrC11, and the intensity of pathogenicity could be ordered as Exiguobacterium sp. > V. splendidus (C13) > V. splendidus (C15).

Ontogenetic changes of innate immune parameters from eggs to early postlarvae of white shrimp Litopenaeus vannamei (Crustacea:Decapoda)

To date, little is known about the immune system during early ontogeny for crustaceans with high commercial value, such as white shrimp (Litopenaeus vannamei). The aim of this study was to characterize several immunological parameters during ontogeny (from eggs to early postlarvae) of L. vannamei under farming conditions. Phenoloxidase activity showed the highest peak 3.6±0.4×10−2U μg−1 at the first nauplius stage, followed by a continuous decrease until dropping to 14% of the peak value in early postlarval (PL) stages. Superoxide dismutase activity reached the highest peak 9.9±0.3×10−3Uμg−1 after metamorphosis to the protozoea stage, then to half that value after metamorphosis to mysis stage and kept dropping until reaching a minimum of 0.5±0.4×10−3Uμg−1 in PL stages. In larval stages peroxidase activity showed a maximum of 2.5±0.4×10−6Uμg−1 after metamorphosis to mysis, and a gradual increase was observed in PL stages until attaining the highest value 4.6±0.8×10−6Uμg−1. Generation of superoxide anion showed a progressive increase after spawning in an evident relationship with growth, reaching the highest value of 7.0±0.4×10−6Uμg−1 in PL-7. To our knowledge, this is the first study that characterizes immunological parameters through the first stages of ontogeny of L. vannamei under farming conditions.

PEMELIHARAAN POST LARVA (PL4-PL9) UDANG VANNAMEI (Penaeus vannamei) DI HATCHERY PT. BANGGAI SENTRAL SHRIMP PROVINSI SULAWESI TENGAH

White shrimp culture have been developed in some part of brackish water pond area in Indonesia, either in extensive, semi intensive or intensive technology and it resulted increasing on Indonesian shrimp culture production. At post larval stages, the pleopods become fully developed and functional. The animals grow very fast in terms of size and are able to swim freely although early post larvae are still planktonic. This research was done to know post larval rearing in Hatchery of PT. Banggai Sentral Shrimp. Preparation of basic facilities such as larval rearing tanks, water supply and aeration system is one of the most important activities in hatchery operation. Good water quality should be strictly maintained especially during this phase of larva rearing.

Naturally-occurring stable isotopes as direct measures of larval feeding efficiency, nutrient incorporation and turnover

Stable isotopes are non-hazardous markers that have been widely-used in assessing energy flow within aquatic ecosystems. Hatchery systems are also highly amenable to this approach, as they represent controlled mesocosms with a limited number of food sources and short planktonic food chains with rapid and measurable bioaccumulation of the heavier stable isotopes of carbon and nitrogen at each trophic step. Differences in the natural isotopic composition of dietary components may be used to provide direct integrated measures of ingestion, nutrient incorporation and growth through development under normal feeding and environmental conditions, in either the laboratory or the hatchery. Simple isotopic mixing models allow estimation of relative utilisation of inert diets and live feeds, and individual components of compound feeds. Such experiments have investigated the effectiveness of co-feeding regimes, optimal timing of live food transitions (e.g. from rotifers to Artemia), presentation of inert diets, optimal size/age for weaning and incorporation of specific dietary components. Furthermore, time series measurement of changes in tissue isotopic signature ( δ 15N, δ 13C) enables modelling of growth dilution and tissue turnover components of isotopic change driven by nutritional sources. These measures need to take into account the difference in isotope values that is typically observed between the diet and consumer (isotopic discrimination factor, Δ). In marine larvae and early postlarvae, Δ 13C and Δ 15N have been found to range widely, from 0.4–4.1‰ and 0.1–5.3‰ respectively. The observation of such a high level of variation within species and life stages indicates a strong effect of diet quality on isotopic discrimination. Elucidating mechanisms underlying such observations, and much greater resolution in larval nutritional studies, can be achieved by application of rapidly-developing techniques for compound specific stable isotope analysis in tracing the transfer of dietary sources of carbon and nitrogen into tissue components. Fast growing aquatic larvae represent excellent model organisms exhibiting rapid transitions in isotopic composition in response to diet, rapidly-changing feeding behaviour and transitions in trophic level with ready ingestion of modifiable experimental diets in short and controlled food chains. Thus results of studies of the effects of diet composition, developmental stage, growth rates or environmental conditions on stable isotope incorporation will be of broad relevance not only in terms of larval nutrition but can also more broadly inform the design and interpretation of ecological studies.

Acquisition of particle processing capability in the oyster Crassostrea gigas: ontogeny of the mantle pseudofeces rejection tracts

Effective particle processing by oysters, in their typically turbid habitats, requires an efficient mechanism of pseudofeces rejection, accomplished by the characteristic oyster mantle rejection tracts. The ontogenetic development of these tracts was studied by means of scanning electron microscopy (SEM) for late larval, postlarval, and juvenile Crassostrea gigas (Thunberg 1793), using hatchery-reared specimens. Pediveliger larvae had a marginal mantle rejection tract, which becomes the inner fold of the 3 mantle folds in postlarval and adult oysters. An ephemeral, secondary marginal ciliary tract was observed in 1.30 mm early postlarvae; this was absent in later postlarval stages. Specimens 2.70 mm in size had a 'tractless' mantle surface, constituting a potentially critical stage with respect to pseudofeces rejection and hence particle processing. The organization of the much more complex adult system, consisting of multiple radial tracts and a marginal collecting tract comprised of 2 contiguous sub-tracts, was not complete until specimens were 10 to 24 mm. The complete re-organization of the mantle rejection system suggests that this is a phylogenetically new character in the Ostreidae. Furthermore, it points to an additional potentially critical event in the acquisition of particle processing capability, especially when considered in the light of previous data on gill development in this species, notably for individuals recruiting in natural habitats.

The effect of larval age on morphology and gene expression during ascidian metamorphosis

Metamorphosis is both an ecological and a developmental genetic transition that an organism undergoes as a normal part of ontogeny. Many organisms have the ability to delay metamorphosis when conditions are unsuitable. This strategy carries obvious benefits, but may also result in severe consequences for older larvae that run low on energy. In the marine environment, some lecithotrophic larvae that have prolonged periods in the plankton may begin forming postlarval and juvenile structures that normally do not appear until after settlement and the initiation of metamorphosis. This precocious activation of the postlarval developmental program may reflect an adaptation to increase the survival of older, energy-depleted larvae by allowing them to metamorphose more quickly. In the present study, we investigate morphological and genetic consequences of delay of metamorphosis in larvae of Herdmania momus (a solitary stolidobranch ascidian). We observe significant morphological and genetic changes during prolonged larval life, with older larvae displaying significant changes in RNA levels, precocious migration of mesenchyme cells, and changes in larval shape including shortening of the tail. While these observations suggest that the older H. momus larvae are functionally different from younger larvae and possibly becoming more predisposed to undergo metamorphosis, we did not find any significant differences in gene expression levels between postlarvae arising from larvae that metamorphosed as soon as they were competent and postlarvae developing from larvae that postponed metamorphosis. This recalibration, or convergence, of transcript levels in the early postlarva suggests that changes that occur during prolonged larval life of H. momus are not necessarily associated with early activation of adult organ differentiation. Instead, it suggests that an autonomous developmental program is activated in H. momus upon the induction of metamorphosis regardless of the history of the larva.

Complete and partial replacement of Artemia nauplii by Moina micrura during early postlarval culture of white shrimp (Litopenaeus schmitti)

Growth rate, soluble protein content, osmotic stress and digestive enzyme activity were studied in early Litopenaeus schmitti postlarvae under different feeding regimens, by partially or completely replacing Artemia nauplii with Moina micrura. Growth was significantly higher in the postlarvae fed with a mixture of M. micrura, Artemia nauplii and algae (0.030 mg dry weight (dw) larva−1 day−1, 17.4 ± 2.1% day−1), together with the postlarvae fed on Artemia nauplii and algae (0.027 mg dw larva−1 day−1, 18.3 ± 1.9% day−1). Complete replacement of Artemia nauplii by M. micrura produced the lowest growth rate (0.018 mg dw larva−1 day−1, 14.3 ± 1.6% day−1) and induced the highest protease and α-amylase activities and lower soluble protein contents. No significant difference among the treatments could be detected in postlarval resistance to osmotic stress. Based on the growth results, soluble protein content, enzymatic activity and osmotic stress resistance, we determined that the partial replacement of Artemia nauplii by M. micrura did not affect the growth, the soluble protein content and the nutritional state in the postlarvae of L. schmitti. To our knowledge, this is the first reported use of M.micrura as feed for early postlarvae of L. schmitti.

Effect of artificial and natural diets on energy allocation in Litopenaeus setiferus (Linnaeus, 1767) and Litopenaeus vannamei (Boone, 1931) early postlarvae

The amounts of energy channeled into growth ( P), maintenance ( R), excretion ( U) and exuviae ( E v) were quantified in six dietary treatments during early postlarval development in Litopenaeus setiferus and Litopenaeus vannamei reared at 28±1 °C and 35±1‰ salinity. The six diet combinations were: (1) freshly hatched Artemia nauplii, (2) freshly hatched Artemia nauplii supplemented with algae, (3) microparticulate commercial diet (MCD), (4) MCD supplemented with algae, (5) Artemia nauplii partially substituted (50%) by MCD and (6) Artemia nauplii partially substituted (50%) by MCD supplemented with algae. Oxygen consumption, ammonia excretion and dry weight were measured from postlarvae day 1 (PL 1) to PL 10 (1 to 10 days after metamorphosis). Energy distribution in both species was affected by diet with significantly higher proportion of energy allocated into production (1.49 J day −1 for L. setiferus and 1.77 J day −1 for L. vannamei) when animals were fed a mixed diet. The proportion of assimilated energy channeled into production ( P/As) was greater when both species were fed mixed diet and was lower when fed on MCD alone or MCD plus algae. On the contrary, the proportion of assimilated energy used in respiration ( R/A) was higher for both species when fed on MCD alone or MCD plus algae, with the lowest values in animals fed on the mixed diet. Low values of net growth efficiency ( K 2) were found in both species when the main food was MCD (alone or supplemented with algae), with the highest K 2 when animals were fed the mixed diet. Results show that divergences between these two species during early postlarval stages only appear when animals were in a poor physiological condition due to an inefficient diet. Artemia nauplii, partially substituted by MCD with a supplement of algae, integrated a high-quality diet for both species producing high net growth efficiency.

An alternative culture system for the hatchery production of abalone without using livefood

Stott's Abalone Postlarval Production System (SAPPS) was developed to replace livefood as the primary means of settling and growing out abalone seed. Culture plates are initially sprayed with microalgal powder/agar gel solution to induce larval settlement. Abalone seed are then raised on an artificial diet/agar gel solution which is sprayed directly onto the culture plates. This study was conducted to test SAPPS on a commercial scale against the diatom biofilm method and two further trials were conducted to investigate the optimum feeding frequency and agar concentration for SAPPS. A total of 100,000 larval Haliotis diversicolor aquatilis were induced to settle onto 90 mucus conditioned commercial rearing plates (5 racks×18 plates each) in 1500-l tanks to test two treatments; diatom biofilm method and SAPPS. The trial was conducted over a 6-week period and the temperature averaged 24.2±1.0 °C. Settlement was similar on all plates in the two treatments. The settlement rate per plate was 17,820±8460 for the diatom biofilm and 17,280±6390 for SAPPS. The postlarval growth rate on the SAPPS plates was over 50% higher than the growth rate on the diatom plates. The final length of postlarvae was significantly higher ( p<0.05) on SAPPS plates (3281±573 μm) than on diatom biofilm plates (2231±314 μm). Furthermore, the survival of postlarvae was also five times higher on SAPPS (51.7%) compared with diatom biofilm (10.6%). SAPPS plates were heavily colonized by marine bacteria which may have acted as a food source for early postlarvae and assisted in the breakdown of polysaccharides. The whole body protein of juveniles was 17.2% in SAPPS compared to 13.3% in diatom biofilm which may suggest that artificial diet was a more balanced and complete nutrient source than diatom biofilm. Smaller scale trials were conducted over 25 days to determine optimum concentration of agar (2.5, 5.0, 7.5 and 10.0 mg/ml) and also to determine specific feed frequency (daily, every second day and every third day). There was no significant difference ( p>0.05) in survival rate in both trials. However, the growth rate of postlarvae at 2.5 mg/ml agar was significantly lower than the other treatments and the leaching rate (% weight loss of food) was double that of agar concentrations 5.0–10.0 mg/ml. Growth rate was highest ( p<0.05) in the feed frequency experiment for postlarvae fed daily and lowest for those fed every third day. The results suggested that agar concentration was optimal at between 5.0 and 10.0 mg/ml with plates being sprayed daily. SAPPS has potential to be used in industry depending on the development of a mechanized, cost-efficient system for spraying the plates.

Moult cycle-related changes in feeding rates of larval krill Meganyctiphanes norvegica and Thysanoessa spp.

Knowledge of crustacean moulting is derived mainly from benthic decapods, which often show profound changes in physiology and behaviour through the moult cycle. In contrast, euphausiids are suggested to be little impaired by moulting, enabling a swarming pelagic life. The aim of this study was to quantify moult cycle-related changes in the feeding activity of 2 euphausiids, Meganyctiphanes norvegica and Thysanoessa spp. Late furcilia larvae and early postlarvae were kept individually over 6 to 7 wk and fed with either a high or low concentration of Artemia salina nauplii or particulate fish food. The intermoult period, similar to9 d for M norvegica and similar to8 d for Thysanoessa spp., increased with body weight, but did not differ with food source. Moulting was partially synchronised, with up to 50 % of the individuals moulting within 48 h of each other. Daily feeding rates on A, salina decreased on the day before moulting, but increased during the next few days with highest values on Days 1 to 3 after moulting. The deviation from the mean feeding rate over the whole moult was more pronounced at the higher food concentration, reaching up to 40 %. Likewise, the defecation volume was reduced on the moulting day and the following day to similar to50 % of the mean, but increased to 180 % of the mean on Day 3 after moulting. Thus, the moult cycle induces significant changes in feeding rates of larval euphausiids with a similar succession of events and intensity as observed in decapods. Feeding rates, extrapolated from spot measurements on a few individuals, are unlikely to represent average values over the whole moult cycle, especially when populations moult synchronously. We propose a protocol to increase the precision of field estimates on feeding rates.

Citrate synthase and pyruvate kinase activities during early life stages of the shrimp Farfantepenaeus paulensis (Crustacea, Decapoda, Penaeidae): effects of development and temperature

Energy metabolism in early life stages of the shrimp Farfantepenaeus paulensis subjected to temperature reduction (26 and 20 °C) was determined using the activities of citrate synthase (CS) and pyruvate kinase (PK). At both temperatures, weight-specific activity of CS decreased throughout the ontogenetic development from protozoea II (PZ II) to postlarva XII–XIV (PL XII–XIV). PK activity reached a pronounced peak in PL V–VI, followed by a further decrease in PL XII–XIV. Temperature reduction produced variation in oxygen consumption rates ( QO 2), ammonia–N excretion and in enzyme activities. Ammonia–N excretion was higher at 20 °C in mysis III (M III), PL V–VI and PL XII–XIV, resulting in substantially lower O:N ratios in these stages. QO 2 was increased in protozoea II (PZ II) and mysis I (M I) at 26 °C, while no difference in QO 2 was detected in the subsequent stages at either temperature. This fact coincided with higher CS and PK activities in M III, PL V–VI and PL XII–XIV at 20 °C compared with 26 °C. Regressions between individual enzyme activities and dry weight exhibited slope values of 0.85–0.92 for CS and 1.1–1.2 for PK and temperature reduction was reflected by higher slope values at 20 than at 26 °C for both enzymes. Weight-specific CS activity was positively correlated with QO 2 at 20 and 26 °C, and may thus be used as an indicator of aerobic metabolic rate throughout the early stages of F. paulensis. The variation in enzyme activities is discussed in relation to possible metabolic adaptations during specific ontogenetic events of the F. paulensis life cycle. Here, the catalytic efficiency of energy-metabolism enzymes was reflected in ontogenetic shifts in behaviour such as larval settlement and the adoption of a benthic existence in early postlarvae. In most cases, enhanced enzyme activities appeared to counteract negative effects of reduced temperature.

Larvae and early post-larvae of Penaeus monodon (Fabricius) experimentally infected with white spot syndrome virus (WSSV) show no significant mortality.

The pathogenicity of white spot syndrome virus (WSSV) was tested with different developmental stages of Penaeus monodon, i.e. nauplius, protozoeae, mysis, early post-larvae (PL1-10), late post-larvae (PL11-20) and juveniles. WSSV challenge was done by immersion and oral routes. No disease occurred in the larvae and early post-larvae but they were positive for WSSV by nested polymerase chain reaction (PCR) assay. Significant mortality was observed in late post-larvae and juveniles and both single and nested PCR assays gave positive results with these samples. The results demonstrated that WSSV virulence in P. monodon increases with advancing stages of development and that WSSV infection does not result in disease for larvae and post-larvae younger than PL10.

Identification of settling and early postlarval stages of mussels ( Mytilus spp.) from the Pacific coast of North America, using prodissoconch morphology and genomic DNA

Detailed inventories of the benthos and field studies of the settlement and recruitment processes of marine benthic invertebrates require accurate identification of newly settled larvae and early juvenile stages. We provide morphological criteria, visible under a good quality dissecting stereomicroscope, by which to discriminate between species of the settling larval and early postlarval stages (∼250 to 700 μm shell length) of mussels of the genus Mytilus on the west coast of Vancouver Island and Southern California. Compared to the bay mussel (M. trossulus), the sea mussel (M. californianus) has: (i) a shallower and flatter umbo, the latter corresponding to a significantly less pronounced prodissoconch I (PI) curvature and (ii) a greater PI length; as well as (iii) a wider separation between the provincular lateral teeth (PLT). The PLT distance is a new term denoting the separation between the midpoint of two reddish pigment spots of the provinculum (larval hinge apparatus) region of settling larvae and early postlarvae of Mytilus spp. from the East Pacific Coast. These spots mark the larger provincular lateral teeth, situated at either end of the provinculum. We confirmed the validity of morphological criteria by comparing PCR products of genomic DNA of provisionally identified postlarvae. Furthermore, measurements of PI lengths and PLT distance from well-preserved postlarvae of sea mussels (M. californianus) and of bay mussels (M. galloprovincialis) from Southern California indicate that the PI morphology and morphometry, and PLT distance criterion apply for that region as well. The criteria presented here can also apply to the advanced (competent) veliger stages, as the latter may settle (i.e. become the “settling” stage) upon encountering a suitable substrate. Our present and previously published work provide economical and effective identification methods that can be used to discriminate among early life history stages (∼250 μm to 5.0 mm shell length) of Mytilus spp. along the west coast of North America.