Pre-hatching Stage Research Articles

The volume and shape of bitterling eggs are more strongly influenced by germ cell autonomy than by the surrounding somatic cells.

There is great variation in the size and shape of teleost eggs from species to species. The size of the teleost egg depends on the amount of yolk accumulated in the egg, which is an important factor directly affecting the survival of hatchlings. Egg shape also contributes significantly to spawning ecology and survival during the prehatching stage. In this study, we used bitterlings, which show a wide variety of egg volumes and shapes, to elucidate whether these factors are determined by germ cells or somatic cells. Reciprocal transplantations of germ cells between two bitterling species revealed that the egg volume was identical to that of the germ cell donor species in both combinations. The egg shape was also very similar to that of the species providing the germ cells. These results suggest that the volume and shape of teleost eggs are greatly influenced by germ cell autonomy.

Mapping of corticotropin-releasing factor, receptors, and binding protein mRNA in the chicken telencephalon throughout development.

Understanding the neural mechanisms that regulate the stress response is critical to know how animals adapt to a changing world and is one of the key factors to be considered for improving animal welfare. Corticotropin-releasing factor (CRF) is crucial for regulating physiological and endocrine responses, triggering the activation of the sympathetic nervous system and the hypothalamo-pituitary-adrenal axis (HPA) during stress. In mammals, several telencephalic areas, such as the amygdala and the hippocampus, regulate the autonomic system and the HPA responses. These centers include subpopulations of CRF containing neurons that, by way of CRF receptors, play modulatory roles in the emotional and cognitive aspects of stress. CRF binding protein also plays a role, buffering extracellular CRF and regulating its availability. CRF role in activation of the HPA is evolutionary conserved in vertebrates, highlighting the relevance of this system to help animals cope with adversity. However, knowledge on CRF systems in the avian telencephalon is very limited, and no information exists on detailed expression of CRF receptors and binding protein. Knowing that the stress response changes with age, with important variations during the first week posthatching, the aim of this study was to analyze mRNA expression of CRF, CRF receptors 1 and 2, and CRF binding protein in chicken telencephalon throughout embryonic and early posthatching development, using in situ hybridization. Our results demonstrate an early expression of CRF and its receptors in pallial areas regulating sensory processing, sensorimotor integration and cognition, and a late expression in subpallial areas regulating the stress response. However, CRF buffering system develops earlier in the subpallium than in the pallium. These results help to understand the mechanisms underlying the negative effects of noise and light during prehatching stages in chicken, and suggest that stress regulation becomes more sophisticated with age.

ВПЛИВ ПОХІДНИХ ТІОСУЛЬФОКИСЛОТ НА МОРФОЛОГІЧНІ ВЛАСТИВОСТІ ЗАРОДКІВ В’ЮНА НА ПОЧАТКОВИХ СТАДІЯХ РОЗВИТКУ

By means of morphological studies, it was established that the influence of thiosulfonate solutions of different structure doesn’t show an inhibition of blastomere division and germ layer formation of the freshwater bony fish, namely weatherfish (MisgurnusfossіlisL). However, under the effect of potassium nitrobenzenethiosulfonate (NTK), at the pre-hatching stage (36thdevelopment stage), that is responsible for the establishment of erythrocyte circulation, external gills predevelopment and the appearance of pigmentation, we observed a delay for approximately 13-16 hours with the imminent vascular pathology. The pronounced changes of cardio-vascular system, which manifested itself in vasodilation, were spotted later on after the NTK influence.The results showed evidence of thiosulfate acid’s derivatives, namely NTK, being promising, highly efficient, non-toxic antithrombotic and antiplatelet remedies.

Establishment of cell lines from individual zebrafish embryos.

With the increasing use of fish as model species for research, cell cultures derived from caudal fin explants as well as pre-hatching stage embryos have provided powerful in vitro tools that can complement or serve as an ethically more acceptable alternative to live animal experiments. The widely-used protocols to establish these lines require, as a starting point, homogeneous pools of embryos or viable adult fish which are large enough for collecting sufficient fin tissue. This excludes the use of fish lines with adverse phenotypes or lines that exhibit mortality at early developmental stages and so can only be propagated as heterozygotes. Specifically, when no visually overt mutant phenotype is detectable for identifying homozygous mutants at early embryonic stages, it is then impossible to sort pools of embryos with the same genotypes to generate cell lines from the progeny of a heterozygote in-cross. Here, we describe a simple protocol to generate cell lines on a large scale starting from individual early embryos that can subsequently be genotyped by polymerase chain reaction. This protocol should help to establish fish cell culture models as a routine approach for the functional characterization of genetic changes in fish models such as the zebrafish. Furthermore, it should contribute to a reduction of experiments which are ethically discouraged to avoid pain and distress.

English

Miticidal action of hexythiazox has been investigated against three mites, Citrus Rust Mite, Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae), False Spider Mite, Brevipalpus californicus (Banks) (Acari: Tenuipalpidae) and Citrus Brown Mite, Eutetranychus orientalis Klein (Acari: Tetranychidae), infesting citrus trees in the region of Al Qassim, Saudi Arabia. Three concentrations of hexythiazox, half of the recommended dose (HRD), the recommended dose (RD) and double recommended dose (DRD) were used against the selected mite species at immature and adult stages. Mortality data was recorded after regular intervals of a day till seven days of post-treatment application. Larvicidal action of the pesticide was observed in terms of post spray percentage of egg hatching. Trails regarding mortality of immature and adult mites were carried out under laboratory and field conditions. A maximum of 72.88% and 64.41% mortality was observed in immature mites of P. oleivora at RD under laboratory and field conditions respectively. The highest mortality of adult mites at RD was recorded again in P. oleivora that was 18.97 and 20.39% under laboratory and field conditions respectively, showing that mortality percentage was insignificant in adults. Under the same conditions, mortality of mites observed at HRD was non-significant and there was negligible increase in mortality when concentration was increased from RD to DRD. Success of hatching for the treated eggs of the three selected mites was observed in the range of 5.00 to 12.50% at the recommended dose. This indicated that hexythiazox has the significant potential of inhibiting hatching process. For the successful control over citrus mites, the appropriate time of spray is prehatching stage

Embryonic and Larval Development of Stinging Catfish, Heteropneustes fossilis, in Relation to Climatic and Water Quality Parameters.

In terms of hatchery-based seed production, one of the most important aquaculture species in Bangladesh is the stinging catfish (Heteropneustes fossilis). Scientific and evidence-based embryonic and larval development research on this fish species in the context of climate change is limited. This experimental study was conducted via induced breeding of stinging catfish using a conventional hatchery system, rearing the larvae in hapas placed in ponds. A series of microscopic observations using a trinocular digital microscope and an analysis of the relationship between larval growth and climate-driven water quality parameters such as temperature, pH, dissolved oxygen, total dissolved solids, alkalinity, and ammonia were performed. During embryonic development, the first cleavage was observed between 30 and 35 min of post-fertilization. Embryonic development (ranging from the 2-cell to the pre-hatching stage) took 21:00 h. Hatching occurred at 22:30 to 23:00 h after fertilization, with an average larvae length of 2.78 ± 0.04 mm. In the post-hatching stage, four pairs of tiny barbels appeared at 36:00 h, and the larvae started feeding exogenously after 72:00 h. These larvae fully absorbed their yolk sacs on the 6th day and attained an average length of 6.44 ± 0.06 mm. Aerial respiration of the larvae was investigated through naked-eye observation on the 10th day of hatching. The average length of the larvae was 32.00 ± 2.0 mm at the end of the 30-day post-hatching observation period. Bivariate correlation analysis showed significant correlations between key climatic variables and water quality parameters under hapa-based larval-rearing conditions. According to canonical correlation analysis, the first canonical function revealed the highest significant correlation between the two sets of variables (r1 = 0.791). The response variable weight of larvae (6.607) was linked to two explanatory variables: pH (0.321) and dissolved oxygen (0.265). For the second canonical correlation function, a positive correlation (0.431) was observed between the two sets of variables. Larval weight (-18.304) was observed to be linked to climatic variables, including air temperature (-0.316) and surface pressure (0.338). Results of this study reveal the subtle correlation between larval growth and water quality driven by climatic variables.

Pre-Hatching Ontogenetic Changes of Morphological Characters of Small-Spotted Catshark (Scyliorhinus canicula)

The small-spotted catshark, Scyliorhinus canicula, provides an optimal model organism to include chondrichthyans in studies comparing morphology or physiology through vertebrate evolution. In particular, for investigations with ontogenetic aspects, there are only a limited number of alternative taxa. Therefore, a detailed staging system is a prerequisite to allowing comparison between different studies. This study supplements information on the latest stages of the established system by Ballard and colleagues in 1993 and complements the respective staging system by including the latest pre-hatching stages. During this phase, some significant ontogenetic shifts happen, e.g., reduction of external gill filament length and complete flattening of rostral angle until Size Class 6, change in the ratio of pre- to post-vent length, and establishment of body pigmentation in Size Classes 7 and 8. All these shifts finally transform the embryo into a hatchling prepared for living outside the eggshell. This study provides a framework allowing comparison of investigations on pre-hatchings of the small-spotted catshark.

Untangling the morphological contradiction: First ontogenetic description of the post-hatching skeleton of the direct-developing frog Brachycephalus garbeanus Miranda-Ribeiro, 1920 (Amphibia: Anura: Brachycephalidae) with comments on the genus miniaturization

The study of ontogenetic series facilitates understanding developmental and evolutionary patterns and processes amongst vertebrate lineages, being widely explored in this taxon over the last decades. However, developmental data for osseous elements of anurans are mostly focused on pre-hatching stages of lineages with a larval stage, with very little data on post-hatching phenotypic transformations, especially in direct-developing anurans. Previous osteological studies of the miniaturized genus Brachycephalus have considered the taxa as a morphological contradiction, given the existence of both paedomorphic and peramorphic traits on the skull and other post-cranial elements. However, none of them have provided a full post-hatching developmental variation of the skeleton for any species of the genus, and thus the observation of such heterochronic changes has remained underexplored. This study aims to provide a detailed developmental description of the osteology of skull and post-cranium osteology of Brachycephalus garbeanus based on an ontogenetic series of 16 post-hatched individuals. Our results show that several skull and post-cranial elements are not fully developed after hatching, with complete bone ossification and fusion occurring at later developmental stages. The combination of our data with previous studies also reinforces the occurrence of delayed skeletal development — i.e., ossification — in Brachycephalus when compared with other brachycephaloids. We also discuss the emergence of morphological novelties — as the skull and axial plates — and structural simplification — as digit reduction/loss — as possible consequences of the extreme miniaturization of the genus.

X-ray microtomography imaging of craniofacial hard tissues in selected reptile species with different types of dentition.

BackgroundReptiles exhibit a large heterogeneity in teeth morphology. The main variability comprises the different tooth shape, the type of tooth attachment to the underlying bone, or the ability to replace the teeth.FindingsHere, we provide full datasets of microtomography scans and 3D models of reptilian dentitions and skulls. We selected representative species for each of 9 reptilian families on the basis of their characteristic dental features. Because there are ≥4 different types of tooth-bone attachments, ranging from the mammalian-like thecodont attachment found in crocodilians to the simple acrodont implantation observed in some lizards, we aimed to evaluate species with different types of tooth-bone attachments. Moreover, another interesting feature varying in reptilian species is the complexity of tooth shape or the number of tooth generations, which can be associated with the type of tooth attachment to the jawbone. Therefore, selected model species also include animals with distinct tooth morphology along the jaw or different number of tooth generations. The development of tooth attachment and relationship of the tooth to the jaw can be further analysed in detail on a large collection of pre-hatching stages of chameleon. Next, we introduce different possibilities for how these datasets can be further used to study tooth-bone relationships or tooth morphology in 3D space. Moreover, these datasets can be valuable for additional morphological and morphometric analyses of reptilian skulls or their individually segmented skeletal elements.ConclusionsOur collection of microcomputed tomography scans can bring new insight into dental or skeletal research. The broad selection of reptilian species, together with their unique dental features and high quality of these scans including complete series of developmental stages of our model species and provide large opportunities for their reuse. Scans can be further used for virtual reality, 3D printing, or in education.

The behavioural and physiological ecology of embryos: responding to the challenges of life inside an egg

Adaptations of post-hatching animals have attracted far more study than have embryonic responses to environmental challenges, but recent research suggests that we have underestimated the complexity and flexibility of embryos. We advocate a dynamic view of embryos as organisms capable of responding - on both ecological and evolutionary timescales - to their developmental environments. By viewing embryos in this way, rather than assuming an inability of pre-hatching stages to adapt and respond, we can broaden the ontogenetic breadth of evolutionary and ecological research. Both biotic and abiotic factors affect embryogenesis, and embryos exhibit a broad range of behavioural and physiological responses that enable them to deal with changes in their developmental environments in the course of interactions with their parents, with other embryos, with predators, and with the physical environment. Such plasticity may profoundly affect offspring phenotypes and fitness, and in turn influence the temporal and spatial dynamics of populations and communities. Future research in this field could benefit from an integrated framework that combines multiple approaches (field investigations, manipulative experiments, ecological modelling) to clarify the mechanisms and consequences of embryonic adaptations and plasticity.

Comparative anatomy and ontogeny of appendicular skeleton of Pseudopus apodus (Pallas, 1775) (Anguimorpha, Anguidae) and a pattern of hindlimb loss in Anguinae.

We present a detailed anatomy of the pectoral girdles, pelvic girdles, and hindlimbs of adult and juvenile specimens of Pseudopus apodus (Pallas, 1775). We compared the individual bones of the appendicular skeleton of P. apodus with those of Anguis fragilis and species of Ophisaurus living in North America, North Africa, and Southeast Asia. We found no anatomical features in P. apodus in common with the species of Ophisaurus living in only North America, North Africa, and Southeast Asia. Additionally, we present the prehatching ontogeny of the pelvic girdle of P. apodus and A. fragilis and the prehatching ontogeny of the hindlimb of P. apodus. In the ontogeny of the pelvic girdle of P. apodus, it is possible to distinguish the ossification centers of ilium, ischium, and pubis. In contrast, in the ontogeny of A. fragilis, no ossification centers of ilium, ischium, and pubis are present, and no hindlimb element was detected. In Stage 1 of ontogeny in Pseudopus, the femur and tibia are present; in Stage 2, the nodule representing the fibula appears; and in Stage 3, in addition to the femur, tibia, and fibula, four tarsal elements are present. This anatomical condition corresponds to the anatomical composition of the hindlimb of the adult O. koellikeri. In Stage 4, the involution of all tarsal elements and fibula begins, and in the last two prehatching stages, only femur and tibia remain; this condition is present not only in the adults of Pseudopus, but also in those of several other species of Ophisaurus.

DLp/HDL-BGBP and MTP Cloning and Expression Profiles During Embryonic Development in the Mud Crab Scylla paramamosain.

Lipids are the main energy source for embryonic development in oviparous animals. Prior to the utilization and catabolism, lipids are primarily transported from the yolk sac to embryonic tissues. In the present study, cDNA encoding a circulatory large lipid transfer protein (LLTP) superfamily member, the precursor of large discoidal lipoprotein (dLp) and high-density lipoprotein/β-1,3-glucan-binding protein (HDL-BGBP), named dLp/HDL-BGBP of 14,787 bp in length, was cloned from the mud crab Scylla paramamosain. dLp/HDL-BGBP was predicted to encode a 4,831 amino acids (aa) protein that was the precursor of dLp and HDL-BGBP, which were both detected in hemolymph by liquid chromatography–mass spectrometry (LC-MS/MS) analysis. For the intracellular LLTP, three microsomal triglyceride transfer protein (MTP) cDNAs of 2,905, 2,897, and 3,088 bp in length were cloned from the mud crab and were predicted to encode MTP-A of 881 aa, MTP-B of 889 aa, and MTP-C of 919 aa, respectively, which were different merely in the N-terminal region and shared an identical sequence of 866 aa. During embryonic development, the expression level of dLp/HDL-BGBP consecutively increased from the early appendage formation stage to the eye pigment-formation stage, which indicated that HDL-BGBP is probably the scaffolding protein for yolk lipid. For the MTP gene, MTP-C accounted for ~70% of MTP mRNA from the blastocyst stage to the nauplius stage, as well as the pre-hatching stage; MTP-C and MTP-A expression levels were comparable from the early appendage formation stage to the late eye pigment-formation stage; MTP-A was extremely low in blastocyst and gastrula stages; MTP-B was expressed at a relatively low-level throughout embryo development. The variations in the expression profiles among MTP transcripts suggested that MTP might play roles in the lipid droplet maturation and lipoprotein assembly during embryonic development.

Embryonic shell shape as an early indicator of pollution in marine gastropods

Gastropods shell shape has been proposed as a good indicator of environmental changes while geometric morphometric (GM) is a powerful tool to detect such changes. Shell shape pattern in adults of the marine gastropod Buccinanops deformis was proved to be correlated with imposex incidence and maritime traffic in populations of Patagonia. We explore through GM the shell shape variation of B. deformis intracapsular embryos in pre-hatching stages of development, in two populations with contrasting maritime traffic and imposex incidence. Embryonic shell shape from polluted and unpolluted areas was significantly different in apex, lateral, aperture and siphonal channel. The same shell shape pattern was observed previously in B. deformis adult specimens. Our results demonstrate that the embryonic shell shape is an early biomarker that could be used as a tool to detect the response to environmental pollution studying abundant egg capsules laid in the field but protecting reproductive adults.

Egg Clutch Survival under Prolonged Paternal Care in a Glass Frog, Hyalinobatrachium talamancae

Previous studies have reported egg attendance as the most common protective behavior among the Neotropical frog family Centrolenidae. However, research on the effect of parental care and other factors thought to affect offspring survival is still missing for a great number of species. Here, we performed field observations during day and night to associate male-only care, habitat characteristics, and environmental variables with egg clutch survival in the understudied glass frog, Hyalinobatrachium talamancae. We conducted 34 nest survival models for 39 egg clutches considering constant daily survival rates, temporal variation in the survival probability, and other biotic and abiotic variables thought to affect the survival of embryos. We found that egg attendance was strongly associated with egg clutch survival in H. talamancae. Our results showed similar degrees of parental investment during day and night, accounting for extensive caring periods over one or multiple clutches as paternal care did not hinder re-mating in this species. Egg clutches exhibited daily survival rates of 0.93±0.02, often reaching pre-hatching stages when attended by males. Our results may thus suggest that egg attendance is a major, if not predominant, determining factor of embryo survival in H. talamancae. This study contributes to the understanding of the natural history associated with paternal care in H. talamancae and provides insight into the evolution of prolonged male-only care in the family Centrolenidae.

Embryonic stage selection for cryopreservation of the silkworm Bombyx mori and the effects of cryopreservation on embryo tissues

Successful cryopreservation of the important silkworm bioresource, Bombyx mori, is essential. In this study, we aimed for successful cryopreservation using vitrification of silkworm embryos. Furthermore, the embryos were assessed for the most appropriate sampling stage. We found that vitrified embryos developed to the serosa ingestion stage when they were vitrified at embryonic stage 24–25. The most suitable stage for vitrification was around a 5–10 h period when the tracheal fibers were elongating in stage 25. None of the vitrified embryos developed into larvae, although some did develop to the pre-hatching stage. From histological analysis, we found that several small cracks formed on the cuticle covering the hypodermis in the vitrified embryos. Additionally, the midgut epithelium was detached from the midgut wall and mixed with the yolk in the midgut lumen. We speculate that the vitrified embryos died from a rapid loss of body water from the small cracks formed in the cuticle. We also suggest that the vitrified embryos may have resulted in dysfunction of the midgut.

The development of hearing abilities in the shark Scyliorhinus canicula.

The few works on audition in sharks and rays concern only adult specimens. We report the hearing abilities in the dogfish Scyliorhinus canicula at different stages, from embryos that still have their yolk sac inside their egg, to juveniles. Hearing development corresponds to an increase in the frequency range from 100-300Hz in early pre-hatching stages to 100-600Hz in juveniles. Modifications in hearing abilities correspond to the development of the brain, the increase of the volume of the membranous labyrinth, the growth of the sensory epithelium, and the development of stereocilia in addition to kinocilium before hatching. This work offers solid insights into the development of hearing abilities that usually can only be inferred from the anatomy of vertebrates or after birth/hatching. It shows also that shark can be sensitive to background noise during development.

Influence of Osmolality and Acidity on Fertilized Eggs and Larvae of Olive Flounder (Paralichthys olivaceus)

The pH of water is one of the main environmental factors exerting selective pressure on marine and freshwater organisms. Here, we focus on the influence of pH on an organism's ability to maintain homeostasis and investigate the effects of acidification on immunity-related genes and osmotic pressure during early development of the olive flounder, Paralichthys olivaceus. The aim of our study was to determine the influence of various pH levels on the fertilized eggs and larvae of P. olivaceus. Gametes of P. olivaceus were artificially introduced and the resulting fertilized eggs were incubated at pH 4.0 (low), 6.0, and 8.0 (equivalent to natural sea water; control). We found that all eggs sank from the water column at pH 4.0. After 38 h, these eggs showed slow development. Hatching occurred more slowly at pH 4.0 and 6.0 and did not occur at all at pH 4.0. Result of gene expression, caspase and galectin-1 were expressed from the blastula to pre-hatch stages, with the exception of the two-cell stage. HSP 70 was also steadily expressed at all pH levels over the five days. The osmolality of fertilized eggs differed marginally at each stage and across pH levels. So, this results demonstrates that low pH level is detrimental to P. olivaceus fertilized eggs.

Morphological and functional development of the spiral intestine in cloudy catshark (Scyliorhinus torazame).

Cartilaginous fish have a comparatively short intestine known as the spiral intestine that consists of a helical spiral of intestinal mucosa. However, morphological and functional development of the spiral intestine has not been fully described. Unlike teleosts, cartilaginous fish are characterized by an extremely long developmental period in ovo or in utero; for example, in the oviparous cloudy catshark (Scyliorhinus torazame), the developing fish remains inside the egg capsule for up to 6months, suggesting that the embryonic intestine may become functional prior to hatching. In the present study, we describe the morphological and functional development of the spiral intestine in the developing catshark embryo. Spiral formation of embryonic intestine was completed at the middle of stage31, prior to 'pre-hatching', which is a developmental event characterized by the opening of the egg case at the end of the first third of development. Within 48 h of the pre-hatching event, egg yolk began to flow from the external yolk sac into the embryonic intestine via the yolk stalk. At the same time, there was a rapid increase in mRNA expression of the peptide transporter pept1 and neutral amino acid transporter slc6a19 Secondary folds in the intestinal mucosa and microvilli on the apical membrane appeared after pre-hatching, further supporting the onset of nutrient absorption in the developing intestine at this time. We demonstrate the acquisition of intestinal nutrient absorption at the pre-hatching stage of an oviparous elasmobranch.

Optimization of vitrification factors for embryo cryopreservation of kelp grouper (Epinephelus moara)

Cryopreservation of marine fish embryos causes to severe cryogenic damage, and to date, adults have not been reared from embryos that were cryopreserved. Here, we optimized vitrification factors to improve the survival and hatching rate of kelp grouper (Epinephelus moara) embryos after cryopreservation. We screened the effects of 11 vitrification solution concentrations (25–50%) on the survival rate of embryos at four developmental stages (16S, 18S, 22S, TB). We investigated the effects of different equilibration time (25–45min) on the survival rate and the influence of vitrification solutions on embryonic volume. In addition, we tested the effects of treating embryos at five different developmental stages (4-6S, 16S, 22S, TB, HB) with different vitrification solutions (35% PMG3S and 35% PMG3T), prechilling temperature (−5 °C and 4 °C) and prechilling time. In total, 9855 embryos were cryopreserved at 10 developmental stages, from optic capsule stage to pre-hatch stage. We found that kelp grouper embryos performed best at equilibration time of 30 min. Embryos at the tail-bud stage exhibited greater tolerance to vitrification than other stages. Vitrification solutions that contained sucrose showed better survival rates compared to embryos treated with vitrification solutions containing trehalose. Pre-chilling treatment improved viability before freezing, but did not improve viability after freezing. In the most optimal condition we identified in this study, the average survival, normal development and malformation rates of cryopreserved embryos were 6.32%, 2.36% and 3.49%, and 39.85% of the surviving embryos that were cryopreserved hatched. The hatched larvae gradually died at day 12 of cultivation, where the longest surviving individuals lived for 16 days. This study provides valuable data for improving survival and hatching rate of cryopreserved grouper embryos, and provides references for further exploring techniques in fish embryo cryopreservation.

A chromosome-level genome of black rockfish, Sebastes schlegelii, provides insights into the evolution of live birth.

The black rockfish (Sebastes schlegelii) is a teleost in which eggs are fertilized internally and retained in the maternal reproductive system, where they undergo development until live birth (viviparity). In the present study, we report a chromosome-level black rockfish genome assembly. High-throughput transcriptome analysis (RNA-seq and ATAC-seq) coupled with in situ hybridization (ISH) and immunofluorescence reveal several candidate genes for maternal preparation, sperm storage and release, and hatching. We propose that zona pellucida (ZP) proteins retain sperm at the oocyte envelope, while genes in two distinct astacin metalloproteinase subfamilies serve to release sperm from the ZP and free the embryo from chorion at prehatching stage. We present a model of black rockfish reproduction, and propose that the rockfish ovarian wall has a similar function to the uterus of mammals. Together, these genomic data reveal unprecedented insights into the evolution of an unusual teleost life history strategy, and provide a sound foundation for studying viviparity in nonmammalian vertebrates and an invaluable resource for rockfish ecological and evolutionary research.