Postlarval Stages Research Articles

Composition of inshore ichthyoplankton community in the Canary islands from a spatial and seasonal perspective: Inshore ichthyoplankton of the Canary Islands

Early life stages of fish are insufficiently studied in most regions around the globe, and consequently, there is an important gap in knowledge on the life cycle of most teleosts. In the Canary Islands (Eastern Central Atlantic), most studies on ichthyoplankton communities are based on traditional net tows in open waters that provide information about early larval stages of pelagic species in the area, while nearshore benthic fish remain highly understudied. In this study, light traps were employed for the first time to assess post-larval stages of neritic fish in this archipelago. A two-year survey was carried out to collect nearshore fish larvae every 6 months at 11 localities from El Hierro, Tenerife and Lanzarote. A total of 3940 fish larvae classified into 13 orders, 28 families and 44 species were collected. These results provide a wide description of the composition of the inshore ichthyoplankton off the Canary Islands, across islands and seasons. Main environmental factors (SST, sea floor orography, oceanographic phenomena …) influencing the population dynamics of this community are discussed. Additionally, the ichthyoplankton assemblages were assessed from the intra-annual perspective, analyzing the species composition and abundances by months and seasons, and providing new insights into reproduction cycles of many common benthic fishes at shallow marine ecosystems of the islands. This study is important to further understand the life cycles of some of the most common fish species in the Canary Islands, unraveling main environmental factors that affect the success of their offspring that sustain populations.

Abrolophus from Australasia, and the mysterious Mypongia (Trombidiformes: Parasitengona: Erythraeidae)

An undetermined species of Abrolophus Berlese was intercepted in quarantine by Australian biosecurity on kiwifruit imported from New Zealand. Here, we show that these are the Australian species Abrolophus ripicola (Womersley, 1934), a species known from the post-larval stages only. We present evidence that the larva of A. ripicola is probably the taxon Mypongia brevipes Southcott, 1961, which belongs to a monotypic genus with unique morphology that is placed in a different subfamily to Abrolophus. The larval and post-larval stages we examined share a similar morphology, most notably a reduction of the prodorsal shield and much reduced leg setation. Three M. brevipes larvae were intercepted on kiwifruit imported from New Zealand, and with an additional larval specimen from South Australia, these four specimens represent the first collections of this taxon since its description. Further circumstantial evidence supporting the conspecificity of the two taxa includes a female specimen of A. ripicola collected from Myponga, the type locality of M. brevipes, and larval stages of an undescribed Mypongia collected together with the post-larval stages of an undescribed Abrolophus, from the same locality in South Africa. Keys are provided for the post-larval stages of Abrolophus species in Australia (6 spp.), Papua New Guinea (Abrolophus novaeguinensis (Gunther, 1941)) and New Zealand (Abrolophus zelandicus Luxton, 1989).

Comparative analysis of transcriptomics and metabolomics provides insights into the mechanisms of VPAHPND invasion and hepatopancreatic damage in Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) poses significant threats to the global shrimp farming industry; however, its molecular mechanisms remain largely unknown. Previous research has primarily focused on comparisons between infected and non-infected states, limiting our understanding of VPAHPND mechanisms. We integrated transcriptomic and metabolomic analyses to investigate the pathogenic mechanism underpinning AHPND in highly vulnerable post-larvae (PL) stage shrimp. By comparing shrimp infected with VPAHPND, those infected with non-VPAHPND, and uninfected shrimp (controls), we identified different VPAHPND infection responses, including significant cytoskeleton and metabolic reprogramming changes. Specifically, VPAHPND infection disturbed lipid, glutathione, and bile acid metabolism, while a key regulatory factor Farnesoid X Receptor (FXR) in these pathways was down-regulated. These findings suggest that VPAHPND manipulates host metabolism to enhance infectivity, leading to severe and irreparable hepatopancreas damage. Our study highlights the molecular interactions between VPAHPND and shrimp, and provides potential targets to mitigate the impact of AHPND in aquaculture.

A comprehensive molecular phylogeny of the terrestrial Parasitengona (Acariformes, Prostigmata) provides insights into the evolution of their metamorphosis, invasion into aquatic habitats and classification

Parasitengona (velvet mites, chiggers and water mites) is a highly diverse and globally distributed mite lineage encompassing over 11,000 described species, inhabiting terrestrial, freshwater and marine habitats. Certain species, such as chiggers (Trombiculidae), have a great medical and veterinary importance as they feed on their vertebrate hosts and vector pathogens. Despite extensive previous research, the classification of Parasitengona is still contentious, particularly regarding the boundaries between superfamilies and families, exacerbated by the absence of a comprehensive phylogeny. The ontogeny of most Parasitengona is distinct by the presence of striking metamorphosis, with parasitic larvae being heteromorphic compared to the predatory free-living deutonymphs and adults. The enigmatic superfamily Allotanaupodoidea is an exception, with larvae and active post-larval stages being morphologically similar, suggesting that the absence of metamorphosis may be either an ancestral state or a secondary reversal. Furthermore, there is disagreement in the literature on whether Parasitengona had freshwater or terrestrial origin. Here, we inferred phylogenetic relationships of Parasitengona (89 species, 36 families) and 307 outgroups using five genes (7,838 nt aligned). This phylogeny suggests a terrestrial origin of Parasitengona and a secondary loss of metamorphosis in Allotanaoupodoidea. We recovered the superfamily Trombidioidea (Trombidioidea sensu lato) as a large, well-supported, higher-level clade including 10 sampled families. We propose a new classification for the terrestrial Parasitengona with three new major divisions (epifamilies) of the superfamily Trombidioidea: Trombelloidae (families Audyanidae, Trombellidae, Neotrombidiidae, Johnstonianidae, Chyzeriidae); Trombidioidae (Microtrombidiidae, Neothrombiidae, Achaemenothrombiidae, Trombidiidae, Podothrombiidae); and Trombiculoidae (=Trombiculidae sensu lato). Adding them to previously recognized superfamilies Allotanaupodoidea, Amphotrombioidea, Calyptostomatoidea, Erythraeoidea, Tanaupodoidae and Yurebilloidae.

NPC Intracellular Cholesterol Transporter 1 Regulates Ovarian Maturation and Molting in Female Macrobrachium nipponense.

NPC intracellular cholesterol transporter 1 (NPC1) plays an important role in sterol metabolism and transport processes and has been studied in many vertebrates and some insects, but rarely in crustaceans. In this study, we characterized NPC1 from Macrobrachium nipponense (Mn-NPC1) and evaluated its functions. Its total cDNA length was 4283 bp, encoding for 1344 amino acids. It contained three conserved domains typical of the NPC family (NPC1_N, SSD, and PTC). In contrast to its role in insects, Mn-NPC1 was mainly expressed in the adult female hepatopancreas, with moderate expression in the ovary and heart. No expression was found in the embryo (stages CS-ZS) and only weak expression in the larval stages from hatching to the post-larval stage (L1-PL15). Mn-NPC1 expression was positively correlated with ovarian maturation. In situ hybridization showed that it was mainly located in the cytoplasmic membrane and nucleus of oocytes. A 25-day RNA interference experiment was employed to illustrate the Mn-NPC1 function in ovary maturation. Experimental knockdown of Mn-NPC1 using dsRNA resulted in a marked reduction in the gonadosomatic index and ecdysone content of M. nipponense females. The experimental group showed a significant delay in ovarian maturation and a reduction in the frequency of molting. These results expand our understanding of NPC1 in crustaceans and of the regulatory mechanism of ovarian maturation in M. nipponense.

An efficient method for raising larvae of sakura shrimp Lucensosergia lucens to the post-larva stage

An efficient method for raising larvae of sakura shrimp Lucensosergia lucens to the post-larva stage

Resistance to initial starvation in stage I larvae of the American lobster Homarus americanus H. Milne Edwards, 1837 (Decapoda: Astacidea: Nephropidae)

Abstract Greater embryo mass confers an advantage in the face of sub-lethal starvation for larvae of the American lobster, Homarus americanusH. Milne Edwards, 1837. We reared larvae in the laboratory and recorded body size, molt increment, stage duration, and mortality during the three larval instars and postlarval stages. Larvae were either fed continuously or subjected to starvation periods immediately after hatching. Larval mass increased with embryo mass suggesting that energetic advantages of heavier embryos are conferred to the larvae. Stage I larvae hatched from clutches with heavier embryos and had lower mortality after five days without food. Stage I duration decreased with increasing embryo mass in treatments with initial periods without food of three, four, and five days. We also observed greater size increase at first molt and larger postlarval size in some treatments. Our results suggest that larger embryos produce larvae that are more resistant to starvation, which may provide a survival advantage when experiencing variable food supply due to the patchy distribution of their planktonic prey.

Analysis of Elimination Effects of Inbreeding on Genotype Frequency in Larval Stages of Chinese Shrimp.

Marine animals possess genomes of considerable complexity and heterozygosity. Their unique reproductive system, characterized by high fecundity and substantial early mortality rates, increases the risk of inbreeding, potentially leading to severe inbreeding depression during various larval developmental stages. In this study, we established a set of inbred families of Fenneropenaeus chinensis, with an inbreeding coefficient of 0.25, and investigated elimination patterns and the manifestations of inbreeding depression during major larval developmental stages. Reduced-representation genome sequencing was utilized to explore the genotype frequency characteristics across two typical elimination stages. The results revealed notable mortality in hatching and metamorphosis into mysis and post-larvae stages. Inbreeding depression was also evident during these developmental stages, with depression rates of 24.36%, 29.23%, and 45.28%. Segregation analysis of SNPs indicated an important role of gametic selection before hatching, accounting for 45.95% of deviation in the zoea stage. During the zygotic selection phase of larval development, homozygote deficiency and heterozygote excess were the main selection types. Summation of the two types explained 82.31% and 89.91% of zygotic selection in the mysis and post-larvae stage, respectively. The overall distortion ratio decreased from 22.37% to 12.86% in the late developmental stage. A total of 783 loci were identified through selective sweep analysis. We also found the types of distortion at the same locus could change after the post-larvae stage. The predominant shifts included a transition of gametic selection toward normal segregation and other forms of distortion to heterozygous excess. This may be attributed to high-intensity selection on deleterious alleles and genetic hitchhiking effects. Following larval elimination, a greater proportion of heterozygous individuals were preserved. We detected an increase in genetic diversity parameters such as expected heterozygosity, observed heterozygosity, and polymorphic information content in the post-larvae stage. These findings suggest the presence of numerous recessive deleterious alleles and their linkage and suggest a major role of the partial dominance hypothesis. The results provide valuable insights into the mechanisms of inbreeding depression in marine animals and offer guidance for formulating breeding strategies in shrimp populations.

The missing metamorphosis: DNA barcoding reveals that Allotanaupodoidea larvae are strikingly similar to post-larval stages</p >

Parasitengona is a diverse group of Prostigmata, including mites with life cycles that include important morphological changes between larva and deutonymph, an evolutionary novelty not shared by its closely related taxa (Halacaridae, Pezidade or Anystidae). Allotanaupodoidea is a superfamily of Parasitengona, known solely by the post-larval instars, that differs from the remaining Parasitengona mainly due to the lack of trichobothria in the prodorsal shield. Allotanaupodoidea has a single family Allotanaupodidae with six species distributed in two subfamilies, Allotanaupodinae Zhang & Fan, 2007 and Paratanaupodinae Zhang & Fan, 2007, with one and two genera, respectively. In the present study, we describe the larva of Allotanaupodus winksi Zhang & Fan, 2007 from New Zealand associated with the deutonymph by means of cytochrome oxidase I barcoding. The description reveals a remarkable resemblance between larval and post larval specimens of A. winksi, a condition approached among Parasitengona only by Calyptostomatidae.

Development of Serotonergic and Dopaminergic Neuronal Networks of the Central Nervous System in King Crab, Paralithodes camtschaticus.

This article presents recent findings as regards distribution of cells producing serotonin and dopamine in the larval central nervous system at different developmental stages, including four pelagic larval stages (zoea I-IV), a semibenthic postlarval stage glaucothoe (megalopa), benthic juveniles, and adult red king crabs, Paralithodes camtschaticus, made by using immunocytochemistry and confocal laser scanning microscopy. We have shown that the serotonergic and dopaminergic neurons are present long before the onset of metamorphosis. In the red king crab b larval nervous system, the changes become particularly pronounced during the first metamorphosis from zoea IV to glaucothoe, which may be related to the development of the segmental appendages and maturation of motor behaviors in decapods. This work presents the distribution and dynamics of the development of serotonergic and dopaminergic neuronal networks in king crab show, the potential roles of serotonin and dopamine in the modulation of olfactory and visual processing in the early stages of larval development, and also the mechanosensory and chemosensory processing in the glaucothoe stage during settlement and in their transition from a pelagic to benthic lifestyle.

Epimorphic development in tropical shallow-water Nymphonidae (Arthropoda: Pycnogonida) revealed by fluorescence imaging

BackgroundExtant lineages of sea spiders (Pycnogonida) exhibit different types of development. Most commonly, pycnogonids hatch as a minute, feeding protonymphon larva with subsequent anamorphic development. However, especially in cold water habitats at higher latitudes and in the deep sea, some taxa have large, lecithotrophic larvae, or even undergo extended embryonic development with significantly advanced postlarval hatching stages. Similar biogeographic trends are observed in other marine invertebrates, often referred to as “Thorson’s rule”.ResultsTo expand our knowledge on the developmental diversity in the most speciose pycnogonid genus Nymphon, we studied the developmental stages of the two tropical representatives N. floridanum and N. micronesicum., We compared classical scanning electron microscopy with fluorescence-based approaches to determine which imaging strategy is better suited for the ethanol-fixed material available. Both species show epimorphic development and hatch as an advanced, lecithotrophic postlarval instar possessing the anlagen of all body segments. Leg pairs 1–3 show a considerable degree of differentiation at hatching, but their proximal regions remain coiled and hidden under the cuticle of the hatching instar. The adult palp and oviger are not anteceded by three-articled larval limbs, but differentiate directly from non-articulated limb buds during postembryonic development.ConclusionsFluorescence imaging yielded more reliable morphological data than classical scanning electron microscopy, being the method of choice for maximal information gain from rare and fragile sea spider samples fixed in high-percentage ethanol. The discovery of epimorphic development with lecithotrophic postlarval instars in two small Nymphon species from tropical shallow-water habitats challenges the notion that this developmental pathway represents an exclusive cold-water adaptation in Nymphonidae. Instead, close phylogenetic affinities to the likewise more direct-developing Callipallenidae hint at a common evolutionary origin of this trait in the clade Nymphonoidea (Callipallenidae + Nymphonidae). The lack of functional palpal and ovigeral larval limbs in callipallenids and postlarval hatchers among nymphonids may be a derived character of Nymphonoidea. To further test this hypothesis, a stable and well-resolved phylogenetic backbone for Nymphonoidea is key.

Growth performance and survival rate of vannamei shrimp (Litopenaeus vannamei) post-larva stages in a super intensive cultivation system with varied densities

Vannamei shrimp (Litopenaeus vannamei) holds significant economic importance in Shrimponesia as a prominent shrimp commodity. The post-larval stage often encounters challenges, primarily due to the shrimp's limited ability to adapt and survive in a new environment. Stocking density is a crucial factor influencing the growth and production performance of vannamei shrimp culture. This study aims to assess the optimal stocking density for achieving optimal growth and survival in L. vannamei. A 40-day maintenance trial was conducted at UD Mina Rahayu Kalianda to investigate the impact of different stocking densities on water quality in the maintenance media. The study utilized containers with varying stocking densities: treatment A (1 shrimp/L), treatment B (1.5 shrimp/L), and treatment C (2 shrimp/L), each with three replications. The findings revealed survival rates (SR) of 83.33% for treatment A, 62.78% for treatment B, and 58.33% for treatment C. Mean Body Weight (MBW) values were recorded as 1.2592 g/shrimp for treatment A, 1.1216 g/shrimp for treatment B, and 0.7728 g/shrimp for treatment C. Average Daily Growth (ADG) results showed 0.0313 g/shrimp for treatment A, 0.0279 g/shrimp for treatment B, and 0.0192 g/shrimp for treatment C. Based on the study, the recommended stocking density for white vannamei shrimp is 40 shrimp/L, demonstrating improved growth and survival rates for this species.

Evaluation of starvation status in the early developmental stages of black rockfish (Sebastes schlegelii) based on morphological and histological characteristics.

Assessing the nutritional status and identifying major causes of mortality in larvae experiencing varying degrees of starvation are crucial for establishing appropriate feeding protocols and enhancing the welfare of hatchery-reared fish. The black rockfish Sebastes schlegelii is an important species in aquaculture and stock enhancement efforts in China, Japan, and Korea. This study aimed to identify optimal diagnostic morphometric indicators of starvation in newly hatched (0-6 days post-hatch, DPH) and postlarval stages (27-37 DPH) of this valuable fish species through histological analyses. Our findings revealed that certain morphometric parameters, including body length, the ratios of eye diameter to head height, body height to body length, and abdomen height to body height, exhibit sensitivity to starvation during both larval and postlarval stages. Particularly, the ratios of body height to body length and abdomen height to body height emerged as the most sensitive morphometric indicators of starvation. Histological examinations of the digestive system revealed rapid alterations in the morphology of hepatic parenchymal cells, accompanied by a significant decrease in the number of lipid cells in the liver during episodes of food deprivation. Starvation induced cellular degeneration in the digestive organs, manifested by reduced heights of epithelial cells and mucosal layers in the intestine, oesophagus, and stomach, along with degeneration and separation of muscle fibers. Among these variables, the height of the intestinal submucosa and muscle layer emerged as the most sensitive indicators reflecting nutritional conditions in newly hatched larvae. In contrast, the height of intestinal striated borders and mucosal folds proved to be the most sensitive indicators in the postlarval stage. Furthermore, the height of intestinal epithelial cells and the number of lipid vacuoles in enterocytes exhibited high sensitivity to food deprivation in both newly hatched larvae and postlarvae. These findings underscore the varying resilience of fish to starvation during different developmental phases and highlight the utility of morphological sensitivity characteristics as reliable diagnostic indices for assessing nutritional status in relation to starvation or suboptimal feeding during the early developmental stages of black rockfish in hatchery-reared processes.

Selection and characterization of ssDNA aptamer targeting Macrobrachium rosenbergii nodavirus capsid protein: A potential capture agent in gold-nanoparticle-based aptasensor for viral protein detection.

The giant freshwater prawn holds a significant position as a valuable crustacean species cultivated in the aquaculture industry, particularly well-known and demanded among the Southeast Asian countries. Aquaculture production of this species has been impacted by Macrobrachium rosenbergii nodavirus (MrNV) infection, which particularly affects the larvae and post-larvae stages of the prawn. The infection has been recorded to cause mortality rates of up to 100% among the affected prawns. A simple, fast, and easy to deploy on-site detection or diagnostic method is crucial for early detection of MrNV to control the disease outbreak. In the present study, novel single-stranded DNA aptamers targeting the MrNV capsid protein were identified using the systematic evolution of ligands by exponential enrichment (SELEX) approach. The aptamer was then conjugated with the citrate-capped gold nanoparticles (AuNPs), and the sensitivity of this AuNP-based aptasensor for the detection of MrNV capsid protein was evaluated. Findings revealed that the aptamer candidate, APT-MrNV-CP-1 was enriched throughout the SELEX cycle 4, 9, and 12 with the sequence percentage of 1.76%, 9.09%, and 12.42%, respectively. The conjugation of APT-MrNV-CP-1 with citrate-capped AuNPs exhibited the highest sensitivity in detecting the MrNV capsid protein, where the presence of 62.5 nM of the viral capsid protein led to a significant agglomeration of the AuNPs. This study demonstrated the practicality of an AuNP-based aptasensor for disease diagnosis, particularly for detecting MrNV infection in giant freshwater prawns.

Reproductive Performance and Larval quality of Freshwater Prawn Broodstock of different water resources

The present study was conducted to compare the reproductive performance and offspring quality of adults of the giant freshwater prawn, Macrobrachium rosenbergii broodstock from four different sites (1) Ganga riverine wild breeders (GW) (2) Ganga riverine pond-reared (GP) breeders (3) Gandak riverine wild breeders (gp); and (4) Gandak riverine pond-reared breeders (gw) were grown out in culture ponds and collected as broodstock at the end of grow-out culture period. M. rosenbergii females were individually stocked for 120 days in three 1500L freshwater recirculation system tanks and fed a commercial diet. Ovarian development, molting and spawning events were checked daily. In addition a number of egg and larval quality parameters were determined. The breeding frequency, fecundity, egg laying success rate, egg dimensions and egg hatchability were not significantly different between animals from the four different sources. However, there were significant differences in terms of offspring quality between the different broodstock sources. Individual dry weight, larval development rate, time to reach the post-larval stage, post-larval survival and tolerance to ammonia toxicity were all better in offspring originating from all broods did not significantly differ in terms of breeding frequency, fecundity and egg dimensions. However, larval quality of Ganga riverine wild and Ganga riverine pond-reared breeders was markedly better than that of Gandak riverine wild reared stock and Gandak riverine pond-reared stock in terms of larval development, survival and post larval production. These results indicate that broodstock sourcing deserves proper attention in hatchery operations of M. rosenbergii. It furthermore proves that domesticated (pond-reared) animals are not necessarily inferior as breeders as compared to wild-sourced animals. The results may also point out the potential to selectively breed stocks with improved characteristics adapted to the local culture environment.

Photographic characterisation of acidification-induced larval malformations in the European lobster Homarus gammarus (Linnaeus, 1758) (Decapoda: Astacidea: Nephropidae)

Abstract Occurrence of developmental malformations is of interest since they potentially influence organismal performance and fitness. We report an increased incidence (⁓ 46 fold) of physical malformations in the larvae of the American lobster Homarus Gammarus (Linnaeus, 1758) in response to seawater acidification (–0.58 pH units relative to nominal pH 8.0). We observed three malformations under the influence of seawater acidification previously undescribed in lobster larvae: a flared carapace, twisted tail, and cross claw. Larvae reared under seawater acidification exhibit significantly lower survivorship (by ⁓14%) and the occurrence of a malformation decreases survivorship (12.7%). Larvae with four types of malformations did not progress through development to reach post-larval stages. Namely, these malformations were a flared carapace, curled carapace, twisted tail, and cross claw. Results from this study provide photographic documentation of various lobster larval malformations that ultimately affect individual success and can be applied for quality-control in hatcheries.

Ontogenetic dynamics of the nudibranch epithelium in Onchidoris muricata (O.F. Müller, 1776)

The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the epithelium, muscles, and elements of connective and nerve tissue. The integument acts as a physical barrier between the external environment and the internal environment that serves to protect and maintain the body of the animal. The body of nudibranch mollusks undergo significant changes during ontogenesis, with the subepidermal space changing as the mollusk grows. As the extracellular subepidermal matrix is modified, the number of collagen fibers increases, muscles and nerves develop, and calcite spicules appear and grow. Yet, specific knowledge pertaining to the transformation of the epithelium is absent. In the present work, the ontogenetic dynamics of the surface epithelium of nudibranch mollusks are traced for the first time using Onchidoris muricata (O. F. Müller, 1776) during the postlarval stages of development. Ontogenetic changes in the epithelium of O. muricata were studied using a complex set of morphological methods. According to our data, the degree of modification to the epithelium in ontogenesis depends on individual body parts and is not consistent throughout. First x-cells were recognized as the probable precursors to sclerocytes.

¿Where do migratory fish spawn in a neotropical Andean basin regulated by dams?

Spawning sites play a key role in the reproduction of fish allowing populations to endure over time. The Nechí River is an important spawning area for potamodromous fish species where one of the threats is dam construction. In order to determine the importance of the Nechí River as a spawning site in the Magdalena River basin, sampling was conducted during the low-water-to-high-water season transition period between 2018 and 2019 at seven sampling sites. The average density of ichthyoplankton was 42.4 ind.10m-3 (SD = 7.1). Of the individuals in the post-larval stage, seven migratory species were identified, and two additional taxa were identified to genus; Prochilodus magdalenae, Megaleporinus muyscorum, and Pseudoplatystoma magdaleniatum presented the greatest density. At the temporal level, the greatest density of larvae of potamodromous species was observed in the first high-water season of 2019 with a total of 5.7 ind.10m-3(SD = 1.044), of which the most representative at the seasonal level were the Cauca River, Magdalena River, and Nechí River before it flows into the Cauca River. There were significant differences in the frequency of embryos and vitelline larvae of the potamodromous species in the interaction of the sampling sites and high-water seasons, as well as with the density of post-larvae. The average drift distance of the spawning areas is roughly 52.1 km. A positive association was found between the volume of turbined water and the presence of ichthyoplankton in the Porce River site, after discharge from the Porce III Hydroelectric Plant. The Nechí River is an important spawning site and there seems to be an association between the increase in ichthyoplankton densities and the distance to the dam (Porce III) as long as there are floodplains along the course of the river.

Sex biased expression of Fem-1 in larval stages suggests its function in early sex differentiation of Litopeneaus vannamei

The Pacific white shrimp Litopenaeus vannamei (L. vannamei) is an economically important species worldwide. As females exhibit a faster growth rate than males, it is crucial to understand the mechanism of sex determination and differentiation for the purpose of mono-sex breeding in shrimp. The feminization-1 gene (Fem-1) serves as a sex-determining gene in Caenorhabditis elegans, and the Fem-1 family is implicated in sex development in several crustaceans. In this study, three Fem-1 family members, namely LvFem-1a, LvFem-1b, and LvFem-1c, were identified and characterized in L. vannamei. Based on genetic sex marker, individuals were separated by sex during the early developmental stages. The expression profiles of these genes were analyzed in female or male larvae. Significant differences between females and males were observed during the early stages of development. In Zoea III or earlier stages, the expressions levels in males were significantly higher than those in females. Intriguingly, there was a shift towards higher expression in females during the mysis and post-larval stages. These findings indicate that the Zoea III stage may be crucial for sex differentiation in shrimp. In addition, the analysis of gene expression across various ovarian stages and tissues was conducted. Results showed that all three genes were highly expressed in the ovary, with particularly elevated levels in ovarian development stage II. These findings suggest that the Fem-1 genes play a critical role in early ovary development. This study is the first research focusing on the sex-specific expression of sex differentiation genes in shrimp. The obtained results provide new insights into to the role of the Fem-1 gene family in sex differentiation and gonadal development.

Seasonal variation of euphausiid life stage and taxonomic composition near the upwelling site northeast of Taiwan

Euphausiids are commercial fishery targets and one of the primary preys of an important component of marine food webs. However, knowledge about the natural life history of euphausiids in the East China Sea is limited. To describe the seasonal variation of euphausiids abundance, diversity, life stage, and taxonomic composition, we visited a site northeast of Taiwan (25.5°N, 121.9°E) in 21 cruises from May 2010 to September 2016. This site is known for an all-year-round upwelling due to the impingement of Kuroshio onto the continental shelf break. We found that the overall euphausiids abundance and diversity tended to be higher in summer to autumn (June to November) compared with spring. In terms of life stages, we found that larval stages (furcilia and calyptopis) predominated in spring when upwelling was prominent, while post-larval stages (juvenile and adult) dominated in summer and autumn when upwelling was weak, and stratification was strong. Moreover, we found that, in spring and summer, Euphausia nana was the dominant species accounting for 90% of total euphausiid abundance, whereas in autumn, Pseudeuphausia latifrons was the dominant species occupying 36% of total abundance. This study provides the foundation to better understand the ecological roles of euphausiids under the influences of upwelling northeast of Taiwan.