Fin Development Research Articles

The functional roles of zebrafish HoxA- and HoxD-related clusters in the pectoral fin development

The paralogs 9–13 Hox genes in mouse HoxA and HoxD clusters are critical for limb development. When both HoxA and HoxD clusters are deleted in mice, significant limb truncation is observed compared to the phenotypes of single and compound mutants of Hox9-13 genes in these clusters. In zebrafish, mutations in hox13 genes in HoxA- and HoxD-related clusters result in abnormal morphology of pectoral fins, homologous to forelimbs. However, the effect of the simultaneous deletions of entire HoxA- and HoxD-related clusters on pectoral fin development remains unknown. Here, we generated mutants with several combinations of hoxaa, hoxab, and hoxda cluster deletions and analyzed the pectoral fin development. In hoxaa−/−;hoxab−/−;hoxda−/− larvae, the endoskeletal disc and the fin-fold are significantly shortened in developing pectoral fins. In addition, we show that this anomaly is due to defects in the pectoral fin growth after the fin bud formation. Furthermore, in the surviving adult mutants, micro-CT scanning reveals defects in the posterior portion of the pectoral fin which is thought to represent latent regions of the limb. Our results further support that the functional role of HoxA and HoxD clusters is conserved in the paired appendage formation in bony fishes.

Characteristics of Morphological Changes in Fins according to Larval Growth of Red Spotted Grouper, Epinephelus akaara.

This study investigated the fin development and morphological characteristics according to larval growth in order to obtain information on behavioral characteristics and optimal stocking density during red seed grouper seed production. To examine the growth and fin development process of the larvae, we randomly sampled at 1, 3, 5, 7, 9, 10, 11, 13, 15, 17, 19, 20, 25, 30, 39, 45, 51, and 72 days after hatching. External morphology was observed and measured using an optical microscope. To observe skeletal development, larvae at 13, 20, 30, and 72 days after hatching were fixed in formalin and stained for cartilage and bone examination. At 9-10 DAH, red spotted grouper larvae (2.74±0.1 to 3.0±0.2 mm TL) exhibited a second dorsal fin spine and pelvic fin spine, which subsequently elongated. At 19-20 DAH, the larvae (5.7±0.1 to 6.1±0.1 mm TL) have the lengths of the second dorsal fin spine and pelvic fin spine average 34% and 31% to total length, respectively. From 30 to 72 DAH (12.6±0.4 to 56.0±0.2 mm TL), the length of the second dorsal fin spine and pelvic fin spine to total length decreased from 27% to 8% for the dorsal fin and 21% to 14% for the pelvic fin, respectively. At 30 DAH (12.6±0.4 mm TL), the larvae reached the complete count of fin rays in each fin. At 39 DAH (20.28±3.07 mm TL), the larvae had fin shapes similar to those of adults. At 13-30 DAH (4.2±0.1 to 12.6±0.9 mm TL), barbs and spinules were distributed along the ridges of the second dorsal and pelvic fin spines. However, at 72 DAH, these barbs and spinules were no longer observed on the fins. During the seed production process, red spotted grouper larvae tend to cluster in the morning, and during this time, entanglement of barbs and spinules on the second dorsal and pelvic fin spines can lead to mortality. Therefore, it is considered essential to focus on managing the behavioral patterns and appropriate rearing density of red spotted grouper larvae from the emergence of barbs and spinules on the second dorsal and pelvic fin spines until they regress and metamorphosis is completed.

INFLUENCE OF TAURINE ON LARVAL EYE DEVELOPMENT AND GROWTH PERFORMANCE OF GOLDEN RABBITFISH (Siganus guttatus)

ARTICLE HIGLIGHTS- Taurine improves eye development in golden rabbitfish larvae- Enhanced growth performance with taurine-enriched rotifers- Taurine positively impacts fish eye and body growthABSTRACTGolden rabbitfish (Siganus guttatus) is an emerging species for aquaculture industry, despite constrains faced on commercial scale of seed production due to the high mortality during the first-feeding stage. An experiment was conducted to determine the effect of taurine through enrichment of rotifers as live-feed on eye development and growth performance of larval golden rabbitfish. Observation of eye development was carried out by measuring eye diameter of the larva and development of the retina based on histology assessment. Growth performance was measured for absolute growth and fin development of the larvae and survival rate. The results showed that taurine-enriched rotifer generally provided better performances for eye development and growth of larval golden rabbitfish compared with control (without taurine). Increase of taurine dose up to 0.050 g/L resulted in an increase of eye diameter, absolute growth, fin development and survival rate. Further increased increment of the taurine tended to decrease the values of the measured parameters. The eye diameter of larval golden rabbitfish fed with 0.050 g/L taurine-enriched rotifer was significantly wider (106.1±9.8 µm) (P < 0.05) compared with control (58.2±14.3 µm), but did not significantly differ from other doses of taurine (P > 0.05). Body width of larvae fed with 0.050 g/L taurine-enriched rotifer was significantly higher (127.3±14.6 µm) (P < 0.05) compared with control (98.8±18.3 µm). In regard to eye development, growth performances (total length, fin development and survival rate), dose of taurine for rotifer enrichment fed to larval golden rabbitfish Siganus guttatus was 0.050 g/L.

Finotypic plasticity: Predator-induced plasticity in fin size, darkness and display behaviour in a teleost fish.

Fish fins are remarkable devices of propulsion. Fin morphology is intimately linked to locomotor performance, and hence to behaviours that influence fitness, such as foraging and predator avoidance. This foreshadows a connection between fin morphology and variation in predation risk. Yet, whether prey can adjust fin morphology according to changes in perceived risk within their lifetime (a.k.a. predator-induced plasticity) remains elusive. Here, we quantify the structural size of five focal fins in crucian carp (Carassius carassius) following controlled manipulations to perceived predation risk (presence/absence of pike Esox lucius). We also assess if crucian carp respond to increased predation risk by shifts in dorsal fin colouration, and test for differences in how fish actively use their dorsal fins by quantifying the area of the fin displayed in behavioural trials. We find that crucian carp show phenotypic plasticity with regards to fin size as predator-exposed fish consistently have larger fins. Individuals exposed to perceived predation risk also increased dorsal fin darkness and actively displayed a larger area of the fin to potential predators. Our results thus provide compelling evidence for predator-induced fin enlargement, which should result in enhanced escape swimming performance. Moreover, fin-size plasticity may evolve synergistically with fin colouration and display behaviour, and we suggest that the adaptive value of this synergy is to enhance the silhouette of deep-bodied and hard-to-capture prey to deter gape-limited predators prior to attack. Together, our results provide new perspectives on the role of predation risk in development and evolution of fins.

Finite Element Analysis Method Design and Simulation of Fins for Cooling a Monocrystalline Photovoltaic Panel

This research focuses on the development and simulation analysis of heat-dissipating fins made of copper, integrated into photovoltaic panels, with the aim of mitigating temperature increases during operation. This initiative arises from evidence that solar panels experience a reduction in energy efficiency when operating at temperatures higher than standard test conditions. The photovoltaic panel was simulated both without fins and with fins under standard test conditions and extreme conditions. The simulation consists of the following steps: design, meshing, selection of physical models and materials, assignment of boundary conditions, validation of the simulation, and interpretation of the results. During validation, results obtained via simulation were compared experimentally, yielding a mean absolute percentage error of 0.28%. It was concluded that the fins with the greatest heat dissipation relative to their area are those of 40 mm height; with this height, the temperature of the photovoltaic panel is reduced by 2.64 K, which represents an efficiency increase of 1.32%. Furthermore, it was concluded from the analyzed data that the efficiency of the fins increases at high temperatures.

Morphological Development and DNA Barcoding Identification of Pholis fangi Larvae and Juveniles in the Yellow Sea

Pholis fangi is a small, bottom-dwelling fish species endemic to the Yellow Sea and Bohai Sea in China. While previous research has focused on its population biology and molecular structure, little is known about the early developmental stages of this species. In this study, larval and juvenile P. fangi specimens were collected from the Sheyang Sea Area, Jiangsu Province, in 2017. Morphological features were examined using microscopy, and DNA barcoding was conducted to confirm species identification. The research documented detailed changes in yolk sac, fin development, and melanophore distribution patterns across larval and juvenile stages of P. fangi. Comparative analysis with other Pholis species revealed that melanophore distribution is a key distinguishing characteristic, allowing effective differentiation between larval and juvenile stages, as well as between Pholis species. This study provides valuable insights into the early life history of P. fangi, contributing to a better understanding of the genus Pholis. The findings demonstrate the utility of combining traditional morphological observation and molecular techniques for accurate species identification, particularly during the critical larval and juvenile developmental phases.

Knockdown of vitamin D receptor affects early stages of pectoral fin development in zebrafish.

The vitamin D receptor (VDR) signalling has been implicated in vertebrate limb or fin formation. However, the involvement of VDR signalling in the early stages of limb/fin development remains to be elucidated. In this study, the role of VDR signalling in pectoral fin development was investigated in zebrafish embryos. Knockdown of vdr induced the severe impairment of pectoral fin development. The zebrafish larvae lacking vdr exhibited reduced pectoral fins with no skeletal elements. Insitu hybridization revealed depletion of vdr downregulated fibroblast growth factor 24 (fgf24), a marker of early pectoral fin bud mesenchyme, in the presumptive fin field even before fin buds were visible. Moreover, a perturbed expression pattern of bone morphogenetic protein 4 (bmp4), a marker of the pectoral fin fold, was observed in the developing fin buds of zebrafish embryos that lost the vdr function. These findings suggest that VDR signalling is crucial in the early stages of fin development, potentially influencing the process by regulating other signalling molecules such as Fgf24 and Bmp4.

Multi-objective optimization and correlation development of HPD-type perforated fins based on fluid–structure interaction analysis

In this study, in combination with the flow behavior of HPD-type fins, an HPD-type perforated fin is proposed, which reduces the flow resistance by an average of 55.9% and improves the comprehensive performance by an average of 22.3%. Subsequently, the thermal–hydraulic performance and stress analysis of HPD-type perforated fins are numerically investigated based on fluid–structure interaction analysis. The findings indicate that the performance of HPD-type perforated fins is highly influenced by the fin width Fw. Moreover, the correlations were established using the RSM concerning the j, f-factor, and the maximum stress, with maximum prediction errors of 8.9%, 19.1%, and 5.8%, respectively. Ultimately, the optimized parameter combination for HPD-type perforated fins was determined through GRA, considering maximum JF-factor and minimal maximum stress as the optimization objectives. The outcomes revealed a notable enhancement in the JF-factor by 96.4% and a concurrent reduction in maximum stress by 3.7% under identical conditions. In conclusion, perforating HPD-type fins proves to be an effective strategy for enhancing both thermal–hydraulic performance and stress distribution.

Genomic screening of fish-specific genes in gnathostomes and their functions in fin development.

In this study, we comprehensively searched for fish-specific genes in gnathostomes that contribute to development of the fin, a fish-specific trait. Many previous reports suggested that animal group-specific genes are often important for group-specific traits. Clarifying the roles of fish-specific genes in fin development of gnathostomes, for example, can help elucidate the mechanisms underlying the formation of this trait. We first identified 91 fish-specific genes in gnathostomes by comparing the gene repertoire in 16 fish and 35 tetrapod species. RNA-seq analysis narrowed down the 91 candidates to 33 genes that were expressed in the developing pectoral fin. We analyzed the functions of approximately half of the candidate genes by loss-of-function analysis in zebrafish. We found that some of the fish-specific and fin development-related genes, including fgf24 and and1/and2, play roles in fin development. In particular, the newly identified fish-specific gene qkia is expressed in the developing fin muscle and contributes to muscle morphogenesis in the pectoral fin as well as body trunk. These results indicate that the strategy of identifying animal group-specific genes is functional and useful. The methods applied here could be used in future studies to identify trait-associated genes in other animal groups.

The dwarf neon rainbowfish Melanotaenia praecox, a small spiny-rayed fish with potential as a new Acanthomorpha model fish: I. Fin ray ontogeny and postembryonic staging.

Fish fins with highly variable color patterns and morphologies have many functions. In Actinopterygii, the free parts of fins are supported by "soft rays" and "spiny rays." Spiny rays have various functions and are extremely modified in some species, but they are lacking in popular model fish such as zebrafish and medaka. Additionally, some model fish with spiny rays are difficult to maintain in ordinary laboratory systems. Characteristics of the small, spiny-rayed rainbowfish Melanotaenia praecox render it useful as an experimental model species. Neither fish age nor body size correlate well with fin development during postembryonic development in this species. A four-stage developmental classification is proposed that is based on fin ray development. Melanotaenia praecox is an ideal species to rear in laboratories for developmental studies. Our classification allows for postembryonic staging of this species independent of individual age and body size. Development of each fin ray may be synchronized with dorsal fin development. We discuss the differences in mechanisms regulating soft, spiny, and procurrent ray development.

Ontogeny of vertebral column and fin development, and detection of deformations in hatchery-reared European Flounder (Platichthys flesus) during early life stage

Understanding the skeletal development and deformations for aquaculture candidate fish species is vital for successful aquaculture practices. Developmental abnormalities at early life stages may reduce fish viability, growth, and wellbeing. This study was carried out to investigate the skeletal ontogeny and skeletal deformities of the European flounder (Platichthys flesus) at early life stage. Artificially produced European flounder larvae (n = 270) were randomly selected at a regular interval (30 fish at each sampling) from hatching to 50 days post-hatch (dph) and their skeletal ontogeny and skeletal deformations were evaluated by using bone and cartilage staining techniques. The average length of fish was 2.71 ± 0.04 mm at 0 dph and reached 19.76 ± 1.7 mm at 50 dph. The notochord began to form at 10 dph and finished flexion at 30 dph. Hypural rays appeared between 10 and 15 dph, followed by appearance of tail fin rays. Urostyle developed at 30 dph and began to ossify at 40 dph. Meristic characters showed an interspecific variation. At least one type of deformation was observed on 23.3% of larvae, and a total of 13 different deformations were identified. The most common deformation was the deformed vertebra which was observed 13 times followed by deformed dorsal fin ray, deformed caudal fin ray, and deformed neural arch and/or spine. Skeletal development during the early life stage of European flounder under culture conditions could be useful for future culture attempts and for early detection of skeletal deformations.

Toxicity of Silver Nanoparticles Synthesized from Opuntia ficus-indica on Danio rerio and Arabidopsis thaliana and Their Antimicrobial Activity

Silver nanoparticles (AgNPs) usefulness has been widely demonstrated in fields such as agriculture, medicine, food, and pharmaceutical industries, primarily for their antibacterial properties. AgNPs synthesized from biological extracts are as effective as those obtained by chemical methods, with the advantage that in the former fewer toxic compounds are generated for the environment. In a previous work, we synthesized AgNPs from the aqueous extract of Opuntia ficus-indica fruit peel (OfAgNPs) and tested their activity against microorganisms from a wastewater treatment plant. OfAgNPs were proposed for use as tertiary wastewater treatment; however, more needs to be known about their antimicrobial activity and toxicological potential. In the present study, the antimicrobial effect of OfAgNPs was demonstrated against reference bacterial strains of Escherichia coli (DH5α), Pseudomonas aeruginosa (ATCC 27853), and Staphylococcus aureus (ATCC 29213), and against fungi isolated in the laboratory and identified as Aspergillus sp., Colletotrichum sp., and Cladosporium sp. In addition, in this work, we report the effects of OfAgNPs produced by exposure in two model organisms: a fish, Danio rerio, and a plant, Arabidopsis thaliana. OfAgNPs in A. thaliana caused negative effects on growth and photosynthetic pigment content only when the exposure was constant and greater than 6 mg/L. However, in D. rerio, impaired caudal fin development was observed at 0.15 mg/L from 24 hr of exposure. This is evidence of the toxicological potential of OfAgNPs, so their use should be carried out in a controlled manner.

Whole-genome Comparisons Identify Repeated Regulatory Changes Underlying Convergent Appendage Evolution in Diverse Fish Lineages.

Fins are major functional appendages of fish that have been repeatedly modified in different lineages. To search for genomic changes underlying natural fin diversity, we compared the genomes of 36 percomorph fish species that span over 100 million years of evolution and either have complete or reduced pelvic and caudal fins. We identify 1,614 genomic regions that are well-conserved in fin-complete species but missing from multiple fin-reduced lineages. Recurrent deletions of conserved sequences in wild fin-reduced species are enriched for functions related to appendage development, suggesting that convergent fin reduction at the organismal level is associated with repeated genomic deletions near fin-appendage development genes. We used sequencing and functional enhancer assays to confirm that PelA, a Pitx1 enhancer previously linked to recurrent pelvic loss in sticklebacks, has also been independently deleted and may have contributed to the fin morphology in distantly related pelvic-reduced species. We also identify a novel enhancer that is conserved in the majority of percomorphs, drives caudal fin expression in transgenic stickleback, is missing in tetraodontiform, syngnathid, and synbranchid species with caudal fin reduction, and alters caudal fin development when targeted by genome editing. Our study illustrates a broadly applicable strategy for mapping phenotypes to genotypes across a tree of vertebrate species and highlights notable new examples of regulatory genomic hotspots that have been used to evolve recurrent phenotypes across 100 million years of fish evolution.

Heterochronic development of pelvic fins in zebrafish: possible involvement of temporal regulation of pitx1 expression.

Anterior and posterior paired appendages of vertebrates are notable examples of heterochrony in the relative timing of their development. In teleosts, posterior paired appendages (pelvic fin buds) emerge much later than their anterior paired appendages (pectoral fin buds). Pelvic fin buds of zebrafish (Danio rerio) appear at 3weeks post-fertilization (wpf) during the larva-to-juvenile transition (metamorphosis), whereas pectoral fin buds arise from the lateral plate mesoderm on the yolk surface at the embryonic stage. Here we explored the mechanism by which presumptive pelvic fin cells maintain their fate, which is determined at the embryonic stage, until the onset of metamorphosis. Expression analysis revealed that transcripts of pitx1, one of the key factors for the development of posterior paired appendages, became briefly detectable in the posterior lateral plate mesoderm at early embryonic stages. Further analysis indicated that the pelvic fin-specific pitx1 enhancer was in the poised state at the larval stage and is activated at the juvenile stage. We discuss the implications of these findings for the heterochronic development of pelvic fin buds.

A staging system for Atlantic herring (Clupea harengus) larvae based on external morphology and skeletal development

AbstractAtlantic herring (Clupea harengus) plays a key role within temperate marine food webs and is targeted by a significant over‐regional fishery. Due to its high economic importance, dynamics in herring stock biomass and recruitment are closely monitored, forming the basis for fisheries management advice. As recruitment patterns translate into the adult stock biomass, early life stage ecology has been thoroughly addressed in fisheries research. Larval monitoring programs commonly focus on length measurements and abundance indices, rarely, information on larval developmental stages is given. As length is highly influenced by temperature, salinity and food availability, their size range can significantly vary between cohorts, populations, and ecotypes. Nowadays, a systematic staging system from the 1970s provides the standard guide for herring larval development, although it does not fully resolve important developmental stages. Here, we propose an improved staging system based on external morphology and skeletal development of herring larvae. The staging system has been developed and tested with herring larvae from different populations of the North and Baltic Sea to ensure applicability. The system comprises 15 stages (+substages) in 5 major developmental phases: the yolk sac phase, the dorsal fin development, the caudal fin development, the pelvic fin development, and the juvenile phase. This staging system aims to simplify herring larval staging to gain a more specific picture of early life dynamics. Because of the detailed description of the development, future studies are better equipped to identify stages which, for example, show high mortality rates and better link them to environmental circumstances.

To the fin and back again: expanding our understanding of congenital limb malformation

Fins are not limbs. However, findings from comparative developmental and genetic analyses show that many of the processes essential in establishing a limb are similar for fin formation. Nevertheless, due to their structural differences, fins are not often used as models to understand the causes or potential treatment of limb disorders.Split hand/foot malformation (SHFM) presents with loss or mis-patterning of elements of hands or feet leading to a ‘clefting-like’ phenotype, often with joining of the digits. This rare disorder is genetically and phenotypically heterogeneous, and knowledge of its etiology remains largely incomplete. Recent work by Truong et al. provides new insight into SHFM by identifying new genetic variants within three different families, predicted to cause changes in function of the PRDM1/Blimp1 gene. PRDM1 is a transcription factor known to be essential for early appendage development in both zebrafish and mice. However, PRDM1 action is nuanced, in part due to its multifaceted roles in integrating signaling, transcription and chromatin state. This complicates the functional characterization of variants in this gene that have unknown significance in SHFM patients. Truong et al. demonstrate the utility of the zebrafish fin as an assay to directly address the function of domain-specific mutations in prdm1a by using the ability of the mutant alleles to rescue fin phenotypes caused by loss of Prdm1a function or, in the case of putative dominant variants, to suppress wildtype zebrafish fin development.A fin may not, or more likely will not, have the complete genetic networks underlying limb development and patterning. However, core mechanisms remain active and, at times, latent in fin development, allowing experimental dissection of mechanisms and gene function. Truong et al. harnessed the experimental malleability of zebrafish to isolate pectoral fin cells in early development and detail Prdm1a-dependent regulation of genes. These data establish aspects of the downstream regulatory network of fin development regulated by Prdm1a, providing insight into the broader array of changes involved in the etiology of this disorder.Core mechanisms and common evolutionary foundations allow for the establishment of defined genetic models of limb disorders in zebrafish and, importantly, accessible experimental models to formulate and test hypotheses on how these disease states are attained. Conversely, identification of disease-associating alleles provides insight into molecular action of genes in development and reveals details of the specificity of their regulation. Fin-in-hand, leading towards new discoveries for congenital limb malformations.

Bmp-signaling and the finfold size in zebrafish: implications for the fin-to-limb transition.

In tetrapods, BMP-signaling coordinates limb outgrowth, skeleton patterning, and apoptosis during the formation of their typical autopod structures, the digits. In addition, inhibition of BMP signaling during mouse limb development leads to the persistence and enlargement of an important signaling center, the apical ectodermal ridge (AER), and consequent digit defects. Interestingly, during fish fin development there is a natural elongation of the AER, rapidly converted into an apical finfold (FF), in which osteoblasts differentiate into dermal fin-rays used in aquatic locomotion. Previous reports have led us to suggest that upregulation of Hox13 genes in the distal fin mesenchyme, caused by the origin of novel enhancer modules, may have caused an increment of the BMP signaling potentially leading to the apoptosis of these osteoblasts precursors of the fin-rays. To explore this hypothesis, we characterized the expression of several components of the BMP signaling in zebrafish lines with distinct FF sizes (bmp2b, smad1, smoc1, smoc2, grem1a, msx1b, msx2b, Psamd1/5/9). Our data suggest that the BMP signaling is enhanced in shorter FFs and inhibited in longer FFs, as implied by the differential expression of several components of this network. In addition, we detected an earlier expression of several of these BMP-signaling components associated with the development of short FFs and the opposite tendency during the development of longer FFs. Thus, our results suggest that a heterochronic shift, involving enhanced Hox13 expression and BMP signaling may have caused the reduction of the FF size during the evolutionary transition from fish fins to tetrapod limbs.

Disruption of T-box transcription factor eomesa results in abnormal development of median fins in Oujiang color common carp Cyprinus carpio.

Median fins are thought to be ancestors of paired fins which in turn give rise to limbs in tetrapods. However, the developmental mechanisms of median fins remain largely unknown. Nonsense mutation of the T-box transcription factor eomesa in zebrafish results in a phenotype without dorsal fin. Compared to zebrafish, the common carp undergo an additional round of whole genome duplication, acquiring an extra copy of protein-coding genes. To verify the function of eomesa genes in common carp, we established a biallelic gene editing technology in this tetraploidy fish through simultaneous disruption of two homologous genes, eomesa1 and eomesa2. We targeted four sites located upstream or within the sequences encoding the T-box domain. Sanger sequencing data indicated the average knockout efficiency was around 40% at T1-T3 sites and 10% at T4 site in embryos at 24 hours post fertilization. The individual editing efficiency was high to about 80% at T1-T3 sites and low to 13.3% at T4 site in larvae at 7 days post fertilization. Among 145 mosaic F0 examined at four months old, three individuals (Mutant 1-3) showed varying degrees of maldevelopment in the dorsal fin and loss of anal fin. Genotyping showed the genomes of all three mutants were disrupted at T3 sites. The null mutation rates on the eomesa1 and eomesa2 loci were 0% and 60% in Mutant 1, 66.7% and 100% in Mutant 2, and 90% and 77.8% in Mutant 3, respectively. In conclusion, we demonstrated a role of eomesa in the formation and development of median fins in Oujiang color common carp and established an method that simultaneously disrupt two homologous genes with one gRNA, which would be useful in genome editing in other polyploidy fishes.

Exposure to different temperature regimes at early life stages affects hatching, developmental morphology, larval growth, and muscle cellularity in rainbow trout, Oncorhynchus mykiss.

In this study, the effects of temperature on hatching, yolk-sac absorption, larval metamorphosis, post-metamorphic growth, developmental morphology, and muscle cellularity were assessed in rainbow trout, during its early development (until 52 days post-hatching, dph). From the eyed-ova stage, embryos were exposed to either low (8 ± 1 °C, LT-8) or high (16 ± 1 °C, HT-16) temperatures until hatching. Following hatching, half of the sac-fry from LT-8 group were shifted to higher temperature (16 ± 1 °C, LHT-16), and half from HT-16 group were shifted to medium temperature (13 ± 1 °C, HMT-13), for larval rearing. Incubating the eyed-ova at 16 °C preceded the hatching by 6 days, synchronized hatching duration, and minimized hatchlings' size-variation. However, it yielded smaller and morphologically less developed individuals compared to those incubated continuously at 8 ± 1 °C. Post-hatch shifting of sac-fry to high and medium temperatures, respectively, from the initial low and high regimes differentially affected the length and weight of fish. The effect on length was immediate and temporary, but on weight, it appeared to be permanent. Red muscle hypertrophy was observed to be high in HT-16 and HMT-13 individuals (high-temperature incubated groups). White muscle hypertrophy was high in HT-16 and LHT-16 individuals (high post-hatch rearing temperature groups). The effect of early-life temperature regimes on developmental morphology was found to be strong at 22 dph (82.5%) and comparatively weak at 52 dph (65%). The post-hatch rearing temperature caused an immediate but temporary effect on fin development, mainly pectoral, caudal, and anal fin (seen only at 22 dph, not at 52 dph). Contrarily, incubation temperature affected fin position, in a delayed but persistent manner (subtle at 22 dph, but stronger at 52 dph). Overall, this study provides new insights on temperature-dependent changes in developmental morphology, muscle cellularity, and larval growth in rainbow trout and shows that incubation temperature affects ontogeny profoundly than post-hatch thermal regimes.

A Comparative Study of the Skeletal Development of Epinephelus fuscoguttatus (♀) and E. tukula (♂) Hybrid Progeny and E. fuscoguttatus

As a new breed of grouper hybrid breeding, EFT has the advantages of delicious flesh, fast growth, and high deformity rate. We explored the metamorphosis and skeletal development of Epinephelus fuscoguttatus and hybrids (EFT) of E. fuscoguttatus (♀) and E. tukula (♂). EFT grew slightly slower than E. fuscoguttatus during the larval period but grew faster during the juvenile period. The sequences of skeletal development were similar in EFT and E. fuscoguttatus. Newly hatched larvae did not have skeletons until 5 days after hatching (DAH) when head cartilage started to develop and complete at 43 days later. The vertebral column started to develop at 11 DAH and was completed at 38 DAH. Pectoral fin development began at 5 DAH and ossification was completed at 48 DAH in EFT and at 43 DAH in E. fuscoguttatus. Anal fin development started at 11 DAH and ossification was completed earlier in EFT than in E. fuscoguttatus. The caudal fins of the two groupers developed at 8 DAH and ossified earlier in EFT than in E. fuscoguttatus. In contrast, E. fuscoguttatus had one additional epural than EFT. These results provide important basic biological data for the growth and skeletal development of pure and hybrid grouper.