Postlarval Stages Research Articles

Molecular cloning and expression pattern of the juvenile hormone epoxide hydrolase gene from the giant freshwater prawn Macrobrachium rosenbergii during larval development and the moult cycle

Juvenile hormone epoxide hydrolases (JHEHs) are regulators of moulting, development and metamorphosis in insects, but we have limited understanding of the roles of these crucial hormonal regulator in crustaceans. In this study, the giant freshwater prawn Macrobrachium rosenbergii was used as a model organism to investigate the role of JHEH in larval development and moulting. We cloned and characterized a JHEH gene from M. rosenbergii (designated as MrJHEH). The full-length cDNA of MrJHEH was 1,682 bp in length, encoding 460 amino acids, and the deduced MrJHEH protein possesses typical features of JHEH family. The phylogenetic analysis revealed that MrJHEH clustered with homologues from crustaceans. Investigation of tissue distribution revealed the abundant expression of MrJHEH in the hepatopancreas. Developmental expression studies showed that the MrJHEH mRNA was expressed throughout the embryo to post-larval stages, with higher expression at late larval stages. Analysis of the moult cycle showed that the expression of MrJHEH mRNA was significantly elevated at the pre-moult stage as compared with the inter-moult level. Both exogenous 20-hydroxyecdysone (20E) injection and eyestalk ablation (ESA) significantly induced the transcription of MrJHEH in cephalothoraxes. These data suggest that MrJHEH is indispensable for the regulation of larval development and ecdysteroidogenesis of M. rosenbergii.

Population growth and mass production of brackish water cladoceran Eurycercus beringi sp. nov. under different diet and salinity regime, and its role in P. indicus larval rearing

The growth performance and mass production of Eurycercus beringi sp. nov., comes under cladocera isolated from Adyar creek, Chennai fed with different diets includes Chlorella sp, Nannochloropsis sp, Chaetoceros sp, Thalassiosira sp, Tetraselmis sp, Dunaliella sp and Isochrysis sp, rice bran and baker’s yeast as monospecific and mixed diets (1:1) have been investigated. The species reproduce parthenogenetically attained a size range of 300- 1098μm and tolerate salinity range of 3–35‰ with fecundity range of 2–7 numbers with minimum maturation period of 3–6 days depending on quality of feed with minimum aeration. Salinity found to play a significant role in survival with maximum survival at 25 ‰. There is a significant difference (p<0.05) in survival at lower and higher salinity. The highest fecundity was observed in the treatment fed with Chlorella and Nannochloropsis sp followed by Chlorella and Thalassiosira sp (1-3×105 cells/ml) i.e. 8 and 7 number of individual/broodstock respectively where as the species attained maturity within 3 days in the treatment fed with Chlorella sp followed by combination of Chlorella and Chaetoceros sp (4 days) and Chlorella and Thalassiosira sp as monospecific diet (4 days each). Mass culture of E. beringi sp. nov. at 100 nos/L was carried out using microalgae, rice bran and baker’s yeast revealed a maximum density 5887 ± 109 nos/L recorded at 30 ‰ within 7 days when fed with mixed diets of Chlorella and Nannochloropsis sp followed by rice bran with baker’s yeast (4586 ± 167 nos/L). Partial replacement of Artemia nauplii with E. beringi sp. nov. (1:1) with highest survival (65 ± 3 %) during early post larval stages of Penaeus indicus revealed its potential to use as live feed in larval rearing. The study highlighted the scope of E. beringi sp. nov. to use as live feed during the larval rearing of brackishwater finfish and shellfishes.

Effect of microencapsulated phenolic compound extracts of Maclura tinctoria (L.) Steud on growth performance and humoral immunity markers of white leg shrimp (Litopenaeus vannamei, Boone, 1931) juveniles

Aim of study: The effect of microencapsulated phenolic compound extracts of Maclura tinctoria (MTBE) on growth performance and humoral immunity markers of the white leg shrimp Litopenaeus vannamei juveniles (0.5 ± 0.2 g initial weight) was studied.Area of study: M. tinctoria was collected from Hampolol, Campeche, and Arroyo del Agua, Culiacan, Sinaloa, Mexico.Material and methods: Three MTBE inclusions (0.5, 1, and 2.5 g MTBE/kg, Purina®) were compared with a control commercial feed (Purina®) during 30 days. Nine phenolic acids, nine flavonols, four dihydro-flavonoids, four flavones, and seven unidentified phenolic compounds were determined fin the MTBE using a Perkin Elmer® HPLC chromatograph and diode array-detection.Main results: The mean concentrations of total phenolic compounds, total flavonoid compounds, and condensed tannins were 198.05 ± 5.59 mg gallic acid equivalent (GAE) g-1 dw, 78.57 ± 1.80 quercetin equivalent g-1, and 28.32 ± 0.33 mg epicatechin equivalent g-1, respectively. The ferric reducing antioxidant power and the total antioxidant capacity, respectively, averaged 28.32 mg GAE mL-1 and 10.9 mg ascorbic acid equivalent mL-1. Survival, weight gain, and specific growth rate of L. vannamei were similar among the experimental diets. The dietary inclusion of MTBE at 0.5 g/kg of food showed significant higher (p &lt; 0.05) plasma hemocyte lysate protein (1.35 ± 0.055 µg mL-1), prophenoloxidase (0.47 ± 0.15, Abs. 492 nm), and superoxide anion (O2.-) activity (0.21 ± 0.07, Abs. 630 nm).Research highlights: The supplementation of MTBE at 0.5 g/kg of food could be considered as a potential alternative additive for L. vannamei diet in the juvenile production, since it improved the response of the humoral immunity markers at post larval life stages, when cultivated shrimp are more susceptible to be infected by pathogens.

Morphological descriptions of the nymph and adults of Ornithodoros clarki, the larva and nymph of Ornithodoros rondoniensis, with notes on their phylogenetic relationships.

Based on tick specimens collected recently in Mexico, Nicaragua, Panama and Brazil, we provide morphological descriptions of the nymph and adults of Ornithodoros clarki Jones & Clifford, 1972 from the first three countries, and the larva and nymph of Ornithodoros rondoniensis (Labruna, Terassini, Camargo, Brandão, Ribeiro & Estrada-Peña, 2008) from Brazil. Also, an analysis of mitochondrial 16S rDNA sequences was performed to analyze the phylogenetic relationships of these tick species. Adults and nymphs of O. clarki and O. rondoniensis are unique among the Argasidae family by presenting exceptionally large spiracular plates with small goblets, and an integument with smooth polygonal mammillae. However, these two species are morphologically distinct based on specific patterns of coxal folds, idiosomal mammillae and pilosity, and female genital flap. In contrast, the larvae of O. clarki and O. rondoniensis are morphologically identical, except for a general larger size of the former species; this slight difference is corroborated by Principal Component Analysis (PCA) by using 40 morphometric variables. Phylogenetic analyses including 16S rDNA partial sequences of different Ornithodoros taxa from Central and South America indicate that O. rondoniensis from Brazil diverges from O. clarki from Mexico, Nicaragua and Panama. However, phylogenetic distance separating both alleged species is similar or slightly lower than the distances depicted for conspecific populations of a few other Ornithodoros species. Nonetheless, our primary criterion to maintain O. rondoniensis as a valid species is because its adult and nymphal stages do present distinct morphological traits that easily distinguish these postlarval stages from O. clarki.

Revision and phylogeny of the genus Andocaeculus (Acari: Caeculidae) I: the A. weyrauchi species group.

Two new caeculid mite species, Andocaeculus beatrizrosso sp. nov. and Andocaeculus burmeisteri sp. nov., are described and A. weyrauchi (Franz, 1964) is redescribed based on material collected at the type locality. All post-larval stages are described for A. weyrauchi and Andocaeculus beatrizrosso sp. nov. and stochastic variation in the idiosomal and appendages chaetotaxy is considered. A clade of Andocaeculus containing the three species (the A. weyrauchi group) is established based on morphological characters, and confirmed with a Bayesian phylogenetic analysis of sequences from the CO1 marker. As result of the same analysis, the absence of the (st) pair of setae on leg II is proposed as a derived condition for the genus Andocaeculus, and the presence of the φ solenidion on leg IV is a derived condition for some Andocaeculus species of the A. weyrauchi species group.

Effects of Microalgae Chlorella vulgaris Density on the Larval Performances of Fresh Water Prawn Macrobrachium rosenbergii (De Man, 1879)

Background: Microalgae have several potential applications in early stages especially in the hatchery phase of several fish, mollusc and crustacean species. The present study aimed to evaluate the effects of microalgae Chlorella vulgaris at different concentrations on larval performances of Macrobrachium rosenbergii. Methods: Freshly hatched larvae were reared until the metamorphosis of first post larval (PL) stage in plastic aquaria (5 liter, 12ppt and 12L:12D) with a density of 10 larvae/liter under five randomly arranged treatment groups in 3 replicates such as, 0×105 (T1, control) and four different concentrations of C. vulgaris 5×105 (T2), 10×105 (T3), 15×105 (T4) and 20×105 (T5) cells/ml. Larvae were fed Artemia (6 nauplii/ml) six times daily. Result: The results revealed that the addition of microalgae in rearing system significantly enhanced (P less than 0.05) the larval survival and developments than without microalgae. The highest larval survival and faster appearance of PL (in days) was observed in T3 group (60.83%, 24.67 days) followed by T4 (56.91%, 28.33 days) T2 (48.39%, 31.33 days) T5 (40.93%, 32.33 days) and T1 (30.65%, 39 days), respectively. Larvae reared at moderate concentrations of microalgae (T3 and T4) resulted in high dry weight that of extreme low (T2) or high (T5) concentrations of microalgae. This study identified the best concentration of Chlorella vulgaris for the rearing of M. rosenbergii larval and could be applicable for the mass larval production of this species commercially.

To the light side: molecular diversity and morphology of stomatopod larvae and juveniles (Crustacea: Malacostraca: Stomatopoda) from crustose coralline algal reefs in Taiwan

Biology of planktonic stomatopod larvae has long remained poorly understood and often considered “black boxes” in life history studies. From coralline crustose algal (CCA) reefs at Datan, Taoyuan, Taiwan, using light traps recently designed, we collected considerable number of stomatopod larvae and juveniles. Applying DNA barcoding techniques using mitochondrial cytochrome oxidase I (COI) and 16S ribosomal RNA (16S rRNA) gene sequences, 14 morphotypes were revealed to represent 12 distinct species, seven of which identified to species level by comparing against reference sequences available from online source (GenBank), whereas the other five do not cluster with any known sequences. All stomatopod larvae and juveniles were described and illustrated. We report Manningia pilaensis (De Man, 1888) and Levisquilla jurichi (Makarov, 1979) as new records of the stomatopod fauna of Taiwan and confirm the validity of Lysiosquillina maculata (Fabricius, 1793). Based on material we acquired from light traps, which include propelagic antizoea larvae (of L. maculata), and also postlarval and juvenile forms (of various squillid species), both positively phototactic, indicating the current understanding of negative-positive-negative phototactic tendency from early planktonic to postlarval stages through the development of stomatopod larvae, might not be as distinct as previously described.

The presence of multiple copies of the vitellogenin gene in Fenneropenaeus merguiensis (De Man, 1888) (Decapoda: Dendrobranchiata: Penaeidae): Evidence for gene expansion and functional diversification in shrimps

Abstract Vitellogenin (Vg) is the precursor of egg yolk that provides nutrients to embryos of oviparous animals. We identified three Vg genes (FmVg1, FmVg2, and FmVg3) from the banana shrimp Fennerpenaeus merguiensis (De Man, 1888) (Penaeidae). The cDNAs ranged from 7,758 to 7,764 bp, and the encoded protein consisted of 2,553–2,585 amino acid residues. The genome structures of FmVg1, FmVg2, and FmVg3 were highly conserved, containing 15 exons and 14 introns. FmVg1-FmVg2, FmVg1-FmVg3, and FmVg2-FmVg3 shared a moderate 52.25%, 60.77%, and 56.45%, respectively. Phylogenetic analysis further revealed that the FmVg1 class vitellogenins are more conserved among the shrimps. The expression patterns of FmVg1, FmVg2, and FmVg3 were similar in the hepatopancreas at different ovarian developmental stages, whereas the expression trends between FmVg1 and FmVg2/3 in the ovary were remarkably different. During ontogenic development, the expression of these Vg genes all reached the highest levels at the post-larval stage. The three Vg genes also exhibited dynamic expression changes at different molting stages, with the highest expression level detected at the intermolt stage. Our study provides evidence that at least three copies of the Vg gene are present in the banana shrimp. These Vg genes are potentially involved in ovary maturation and larval development, and the divergence in their sequences, structures, and expression dynamics reflects their functional diversification in F. merguiensis. The expression of these Vg genes is therefore tightly regulated spatially and temporally. This is the first report for the molecular characterization of multiple vitellogenin genes in shrimps. Our results indicate that the vitellogenin gene is multi-functional and shows a non-sex specific expression pattern.

Ecological adaptation in European eels is based on phenotypic plasticity

The relative role of genetic adaptation and phenotypic plasticity is of fundamental importance in evolutionary ecology [M. J. West-Eberhard, Proc. Natl. Acad. Sci. U.S.A. 102 (suppl. 1), 6543-6549 (2005)]. European eels have a complex life cycle, including transitions between life stages across ecological conditions in the Sargasso Sea, where spawning occurs, and those in brackish and freshwater bodies from northern Europe to northern Africa. Whether continental eel populations consist of locally adapted and genetically distinct populations or comprise a single panmictic population has received conflicting support. Here we use whole-genome sequencing and show that European eels belong to one panmictic population. A complete lack of geographical genetic differentiation is demonstrated. We postulate that this is possible because the most critical life stages-spawning and embryonic development-take place under near-identical conditions in the Sargasso Sea. We further show that within-generation selection, which has recently been proposed as a mechanism for genetic adaptation in eels, can only marginally change allele frequencies between cohorts of eels from different geographic regions. Our results strongly indicate plasticity as the predominant mechanism for how eels respond to diverse environmental conditions during postlarval stages, ultimately solving a long-standing question for a classically enigmatic species.

Synbiotic containingKappaphycus alvarezii, Spirulinasp.andHalomonas alkaliphilaimproves survival, growth and vibriosis resistance in whiteleg shrimp (Litopenaeus vannamei) post-larval culture

The high losses in shrimp production due to mortality caused byVibrioopportunistic pathogens still constitute a significant challenge in the shrimp industry. Synbiotic feed supplementation appears to be a promising control strategy to maintain healthy shrimp stock. In this study, the effects of synbiotic-containing prebiotic seaweedsKappaphycus alvareziiandSpirulinasp. as well as probioticHalomonas alkaliphilawere evaluated on the survival, growth, and vibriosis ofLitopenaeus vannameiduring the post-larval stage. Five different feeds were tested: commercial feed, prebioticsK. alvareziiandSpirulinasp.-supplemented feed, and synbiotic-supplemented feed usingK. alvarezii, Spirulinasp. and probioticH. alkaliphilawith different concentrations of 108, 109, and 1010CFU.kg−1. Following 14 days after the feeding test, the highest shrimp survival (91.46 ± 0.05%) was obtained in the treatment group fed with synbiotic-supplemented feed containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 109CFU.kg−1(p&lt; 0.05). A 7-day challenge test against opportunistic bacteriaVibrio harveyiiwas then performed using three treatment groups: (1) synbiotic, containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 109CFU.kg−1; (2) prebiotic, with 0.375%K. alvarezii, 0.125%Spirulinasp.; and (3) control, using commercial feed. The highest shrimp survival of (79.9 ± 0.05%) was found in the synbiotic treatment group, followed by the prebiotic and control treatment groups (p&lt; 0.05). Overall results suggested that synbiotic-supplemented feed containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 109CFU.kg−1significantly improved shrimp survival even when challenged withV. harveyii. Thus, this synbiotic can be potentially applied as an alternative biocontrol strategy against vibriosis in intensive shrimp post-larval culture.

&lt;p class="ZootaxaTitle"&gt;&lt;strong&gt;Transformative nototchaetae: larval development and metamorphosis in &lt;em&gt;Chrysopetalum &lt;/em&gt;spp. (Chrysopetalinae: Chrysopetalidae: Annelida)&lt;/strong&gt;&lt;/p&gt;

The morphology of an early nectochaete larva belonging to Chrysopetalum sp. is aligned with that of a planktotrophic larva at a crucial stage of benthic settlement: an entire provisional spinose notochaetal scleritome, large episphere with prostomial nascent sensory structures and larval podia and cirri of the anterior two segments in transition. Morphological sequences of post-larvae and juveniles, common to a number of Chrysopetalum species, indicate that long, slender, provisional, camerate notochaetal spines are replaced during metamorphosis and growth with an entire adult, camerate notochaetal scleritome consisting of broad paleae with internal, longitudinal ribs. The Chrysopetalum sp. six segment larva supports achaetous notopodia I and chaetous notopodia II, each with a pair of dorsal cirri, ie. 4 cirri in total; segment II has acirrose neuropodia. Individuals of post-larvae and juvenile Chrysopetalum species, 8–15 segments, possess a total of 6 cirri on segments I and II: segment I with a pair of tentacular dorsal cirri and the formation of a pair of tentacular ventral cirri, and segment II comprising a pair of dorsal cirri, spinous notochaetae and acirrose neuropodia. During metamorphosis the acirrous neuropodia of segment II are reabsorbed and replaced in stages with a pair of ventral tentacular cirri until the adult state is achieved: achaetous segment 1 with two pairs of tentacular cirri and segment II similar, ie. total of 8 cirri. The cirri arrangement of segments I and II before final metamorphosis in post-larval stages of Chrysopetalum species is, interestingly, that described for adults in the majority of other Chrysopetalinae taxa. Ontogenetic developmental processes of formation and loss of acirrose neuropodia and replacement of spinose larval notochaetae with adult paleae observed in Chrysopetalum species are compared with species of other taxa of the Chrysopetalinae.

On-site detection of nodavirus in post larval (PL) stage of the giant prawn, Macrobrachium rosenbergii: A test to nip the problem in the bud

Macrobrachium rosenbergii nodavirus (MrNV) affects the larval, post-larval, and juvenile stages of M. rosenbergii, the giant freshwater prawn, causing white tail disease (WTD). With its high mortality, WTD is a severe threat to shrimp and prawn farming. We describe the development and optimization of an antibody-based lateral flow assay (LFA) for the early detection of MrNV in the post-larval (PL) stage of M. rosenbergii. The LFA parameters (viz., the detergent concentration, GNPs-antibody conjugate, antibody concentration applied to the test line and membrane porosity) were optimized using the design of experiment (L9 orthogonal array). Under optimized conditions, MrNV could be detected within 20 min with high specificity, reproducibility, and sensitivity (LOD = 104 particles/ng of total RNA). In virus challenge experiments, MrNV could be detected on the seventh day of infection in the PL stage. LFA was validated using infected PL samples collected from the field (hatcheries and nurseries) (n = 80) in conjunction with ‘gold standard’ qRT-PCR test. High sensitivity (100%) and specificity (90%) of LFA, with a Cohen's kappa coefficient of 0.936, suggested ‘good agreement’ between the developed LFA and qRT-PCR. The developed LFA has an immense potential of averting losses by rapid detection of MrNV at PL stage in M. rosenbergii.

Identification of two genes potentially related to myogenesis and muscle growth in Fenneropenaeus chinensis: Activin receptor II and Follistatin-like protein

Activin receptor (ActR) and follistatin-like (FSTL) genes, which are involved in the Myostatin (Mstn) related TGF-β/Smad signaling pathway, play important roles in regulating the muscle generation, development and growth of muscle in vertebrate. Our previous studies have confirmed that Mstn negatively regulates muscle development and growth in Fenneropenaeus chinensis as that in vertebrate. However, the roles of ActR and FSTL in muscle development and growth in invertebrate remains unclear. In the present study, type II ActR(FcActRII) and FSTL (FcFSTL) genes from F. chinensis were cloned and characterized, and their functions on muscle development and growth were investigated. The full-length cDNAs of FcActRII and FcFSTL were 2366bp that encoded 572 amino acids and 2474bp that encoded 717 amino acids, respectively. Sequence analysis revealed that the overall protein sequences of the two genes shared 97% and 96% identities with Penaeus vannamei and 50%-59% and 35%-36% identities with vertebrates, respectively. In the early development stages, muscles firstly appeared in nauplius stage and developed gradually until post larval, and the mRNA expressions of FcActRII increased from gastrula to zoea stage and then decreased from zoea stage to post larval stage while that of FcFSTL was lowest in gastrula stage and increased rapidly in nauplius stage and then expressed stably from nauplius stage to post-larval stage. In the adult shrimp, the two genes were widely distributed in the examined tissues. The FcActRII expression in muscle of L group was significantly lower than that of S group, but the FcFSTL expression showed an opposite result. After down-regulating the expression of FcMstn by RNAi, FcActRII expression was significantly down-regulated while that of FcFSTL was up-regulated. The present study suggested that FcActRII and FcFSTL, regulated by FcMstn, might be involved in myogenesis and muscle growth.

Survival, growth, and radula morphology of Haliotis kamtschatkana postlarvae fed six species of benthic diatoms

Haliotis kamtschatkana is the only abalone native to the Pacific Northwest of North America. Haliotis kamtschatkana populations are in decline, and current restoration efforts in Washington State rely on out-planting hatchery-produced juveniles. Hatchery personnel report highest mortalities in the postlarval stage of H. kamtschatkana, mainly during the first 3 to 6 months. Postlarvae feed on films of benthic diatoms, and the purpose of this study was to test six diatom species (Achnanthes brevipes, Amphora salina, Amphiprora paludosa, Cylindrotheca closterium, Navicula incerta, and Nitzschia laevis) as suitable diets for H. kamtschatkana. Diatom diet suitability might rely on several factors, including diatom characteristics as well as the postlarva's ability to ingest the diatoms. The radula is a crucial feeding structure for gastropods and may display morphological plasticity, but this has never been characterized in H. kamtschatkana. We investigated survival, growth, and radula morphology of H. kamtschatkana postlarvae when fed one of six benthic diatom species for 61 days post-settlement. Amphora salina yielded the highest survival, in a statistically homogenous subgroup with N. incerta, A. paludosa, and C. closterium. Achnanthes brevipes yielded exceptionally low survival, on par with a starvation control. Cylindrotheca closterium yielded significantly better growth than all other diets except A. salina. Radula development was similar to that of other abalone species. The shape and size of the radula did not explain success or failure of any of the diatom diets since the radula morphology of H. kamtschatkana was comparable to other abalone that have succeeded when fed these same diets. We found no relationship between diatom diet and radula morphology. We recommend A. salina as a suitable diet for newly settled H. kamtschatkana postlarvae, and that a combination of A. salina and C. closterium be used to supplement feeding on naturally occurring biofilms.

Early life trophodynamic influence on daily growth patterns of the Alboran Sea sardine (Sardina pilchardus) from two distinct nursery habitats (bays of málaga and almería) in the western Mediterranean Sea

The Alborán Sea sardine (Sardina pilchardus) is the most abundant small pelagic fish in the Mediterranean Sea. Along the northern coast of the Alborán Sea, Málaga and Almería Bay are two important nursery grounds with contrasting oceanographic characteristics. Post-larval stages of S. pilchardus were collected during the late autumn and late winter along with the mesozooplankton community. We examined the influence of feeding behavior on larval growth using environmental variables, daily growth metrics, otolith biometry, stable isotope analysis and trophodynamics. Trophic positions were calculated using mesoozooplankton as potential prey for S. pilchardus. During both seasons, we observed faster growth in larger otoliths that also corresponded to higher trophic positions. Our results indicate that the isotopic signature of larvae is highly influenced by the mesozooplankton community structure. Moreover, the trophic variables showed a significant linear relationship with the estimated ages for all larvae indicating dietary changes throughout ontogenic development.

Functional morphology and post-larval development of the buccal complex in Eubranchus rupium (Nudibranchia: Aeolidida: Fionidae)

Nudibranch molluscs represent an interesting model group to study the evolution of feeding apparatus and feeding modes, being characterized by specialized buccal complex in combination with extremely diverse dietary preferences and multiply prey shifts in evolutionary history. However, the plasticity of the buccal complex morphology in response to diet and specific feeding modes remains understudied. Here we study the general morphology and ontogenesis of the buccal complex in Eubranchus rupium (Nudibranchia: Fionidae). Specific goals are to provide a detailed description of buccal structures morphology in post-larval stages, suggest the feeding mechanism and discuss the phylogenetic value of the morphological characteristics of buccal armature within the genus Eubranchus. Methods included in vivo observations of the feeding process for E. rupium, light microscopic methods, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (cLSM). According to our results, E. rupium is a mechanical driller, boring holes in hydrozoan perisarc and sucking internal content. The mechanical drilling is supplied by functionally uniserial radula with plate-like laterals teeth of exclusively supportive function and by massive buccal musculature. Comparative phylogeny-based analysis suggests that the drilling feeding mode is common for the genus Eubranchus and indicates radular characters may have a high phylogenetic signal. The buccal complex morphology and feeding mode were found to be similar in both adults and post-metamorphic specimens, its general structures occur even in settled veligers. Juveniles and adults compete for food source, but the competition is smoothed due to characteristics of prey species growth and life cycle.

The dynamics of epidermal stratification during post-larval development in zebrafish.

The epidermis, as a defensive barrier, is a consistent trait throughout animal evolution. During post-larval development, the zebrafish epidermis thickens by stratification or addition of new cell layers. Epidermal basal stem cells, expressing the transcription factor p63, are known to be involved in this process. Zebrafish post-larval epidermal stratification is a tractable system to study how stem cells participate in organ growth. We used immunohistochemistry, in combination with EdU cell proliferation detection, to study zebrafish epidermal stratification. For this procedure, we selected a window of post-larval stages (5-8 mm of standard length or SL, which normalizes age by size). Simultaneously, we used markers for asymmetric cell division and the Notch signaling pathway. We found that epidermal stratification is the consequence of several events, including changes in cell shape, active cell proliferation and asymmetrical cell divisions. We identified a subset of highly proliferative epidermal cells with reduced levels of p63, which differed from the basal stem cells with high levels of p63. Additionally, we described different mechanisms that participate in the stratification process, including the phosphorylation of p63, asymmetric cell division regulated by the Par3 and LGN proteins, and expression of Notch genes.

Morphometric and genetic variations of species composers of nike fish assemblages in Gorontalo Bay Waters, Indonesia

Abstract. Sahami FM, Kepel RC, Olii AH, Pratasik SB, Lasabuda R, Wantasen A, Habibie SA. 2020. Morphometric and genetic variations of species composers of nike fish assemblages in Gorontalo Bay Waters, Indonesia. Biodiversitas 21: 4571-4581. Nike is Gobioidei fish at the post-larval and juvenile stages whose habitat is still in seawater before they migrate to the freshwater, grow up, and spawn to fulfill their life cycle as an amphidromous species. This study aims to identify the species composers of Nike fish in Gorontalo Bay waters based on their morphometric and molecular characters. 2,523 samples were collected from the catches of fishermen during three periods of their appearance in Gorontalo Bay waters from January to March 2019. The samples were grouped based on their similarity of melanophore patterns, and morphometric characters of 10 units were then measured. This study found 20 different groups of melanophore patterns; 15 of them were new melanophore patterns. DNA samples from each group of new melanophore patterns were then isolated for molecular analysis. The morphometric analysis grouped the 20 melanophore patterns into three separate clusters that were confirmed through molecular analysis. The results of Gen Cytochrome Oxidase I (COI) sequences indicate that the new melanophore patterns of Nike fish assemblages consisting of six species; five species in the Gobiidae family (i.e. Sicyopterus parvei, S. cynocephalus, S. longifilis, S. lagocephalus, and Stiphodon semoni) and a species in the Eleotridae family (Belobranchus belobranchus).

Expected ocean warming conditions significantly alter the transcriptome of developing postlarval American lobsters (Homarus americanus): Implications for energetic trade-offs

The American lobster (Homarus americanus) is one of the most iconic and economically valuable fishery species in the Northwestern Atlantic. Surface ocean temperatures are rapidly increasing across much of the species' range, raising concern about resiliency in the face of environmental change. Warmer temperatures accelerate rates of larval development and enhance survival to the postlarval stage, but the potential costs at the molecular level have rarely been addressed. We explored how exposure to current summer temperatures (16 °C) or temperature regimes mimicking projected moderate or extreme warming scenarios (18 °C and 22 °C, respectively) for the Gulf of Maine during development influences the postlarval lobster transcriptome. After de novo assembling the transcriptome, we identified 2542 differentially expressed (DE; adjusted p < 0.05) transcripts in postlarvae exposed to 16 °C vs. 22 °C, and 422 DE transcripts in postlarvae reared at 16 °C vs. 18 °C. Lobsters reared at 16 °C significantly over-expressed transcripts related to cuticle formation and the immune response up to 14.4- and 8.5-fold respectively, relative to those reared at both 18 °C and 22 °C. In contrast, the expression of transcripts affiliated with metabolism increased up to 7.1-fold as treatment temperature increased. These results suggest that lobsters exposed to projected warming scenarios during development experience a shift in the transcriptome that reflects a potential trade-off between maintaining immune defenses and sustaining increased physiological rates under a warming environment. This could have major implications for post-settlement survival through increased risk of mortality due to disease and/or starvation if energetic demands cannot be met.

Larval development of a new hybrid Malaysian mahseer (Barbonymus gonionotus ♀ × Tor tambroides ♂)

Hybrid Malaysian mahseer is a crossbreed between the male Malaysian mahseer, Tor tambroides and female silver barb, Barbonymus gonionotus through induced breeding. The study was carried out to observe the morpho-histological development of the F1 hybrid Malaysian mahseer larvae for the entire duration of its larval stage. Newly hatched larvae were reared in three 120 L aquaria at a stocking density of 5 larvae per liter. Larval development was observed daily from 1 to 9 DAH (day after hatching) and at 2-day intervals until 25 DAH by means of light and scanning electron microscopy (SEM), and histology. Newly hatched larvae had tiny body with closed mouth and simple gut formation. The hybrid larvae commenced exogenous feeding by 3 DAH using the taste buds and neuromasts to detect the presence of foods. Larval eyes were underdeveloped in early stage. They became fully functional as early as 9 DAH with larval TL and BW of 8.36 ± 0.24 mm and 4.3 ± 0.14 mg, respectively. By 7 DAH the stomach and intestinal tract were completely developed while complete tissue layers (mucosa, submucosa, muscularis and serosa) were visible in the larval gut by 18–21 DAH indicating the end of the larval stage. The post larval stage of the hybrid Malaysian mahseer was short and completed by 21–25 DAH when the scales fully covered its body. The rapid completion of larval stages and morphological features took after the maternal brood-fish, Barbonymus gonionotus but with larger scales. These positive attributes in larval development could be of interest to the aquaculture industry.