Reproductive performance of lumpfish (Cyclopterus lumpus, L. 1758) females: Effects of integrated photoperiod and temperature manipulations on sexual maturation and spawning.

A successful control of sexual maturation is crucial for year-round production of lumpfish juveniles destined as cleaner fish in Atlantic salmon aquaculture. This study investigated the combined effects of photoperiod and temperature manipulations on sexual maturation and spawning in lumpfish females. Lumpfish juveniles were exposed to simulated natural and nine-month compressed annual photoperiods, with subsequent temperature elevation.

Gene Expression and Phenotypic Assessment of Egg Quality across Developmental Stages of Atlantic Cod throughout the Spawning Season.

Egg quality in fishes is commonly determined by fertilisation success and cleavage patterns as a phenotypic outcome of underlying regulatory mechanisms. Although these phenotypic estimators of egg quality are useful in farming conditions, these "good quality" egg batches do not always translate to good larval growth and survival. The identification of genes involved in embryonic development may help find links between genetic factors of maternal origin and egg quality.

Ultrasonic imaging as a means of monitoring gonadal development in lumpfish (Cyclopterus lumpus).

The commercial farming of juvenile lumpfish requires monitoring of gonadal development to achieve synchronized production. Conventional methods such as gonadosomatic index (GSI), sex hormone analyses, gonadal histology, endoscopy, and gene expression analyses are costly, invasive, and often involve sacrificing the fish. We assessed the efficiency of ultrasound as a non-invasive method for monitoring gonadal development in lumpfish.

Impact of germ cell ablation on the activation of the brain-pituitary-gonadal axis in precocious Atlantic salmon (Salmo salar L.) males.

The germ cells are essential for sexual reproduction by giving rise to the gametes, but the importance of germ cells for gonadal somatic functions varies among vertebrates. The RNA-binding dead end (Dnd) protein is necessary for the specification and migration of primordial germ cells to the future reproductive organs. Here, we ablated the gametes in Atlantic salmon males and females by microinjecting dnd antisense gapmer oligonucleotides at the zygotic stage.

Sex steroid dynamics and mRNA transcript profiles of growth- and development-related genes during embryogenesis following induced follicular maturation in European eel.

Hormones and mRNA transcripts of maternal origin deposited in the egg may affect early embryonic development in oviparous species. These hormones include steroids, such as estradiol-17β (E2), testosterone (T), 11-ketotestosterone (11-kt), 17α,20ß-dihydroxy-4-pregnen-3-one (DHP), and cortisol, which also play an important role in fish reproduction. In European eel, Anguilla anguilla, which does not reproduce naturally in captivity, vitellogenesis in female broodstock is commonly induced by administration of salmon or carp pituitary extract (PE) as an exogenous source of gonadotropins, while follicular maturation is stimulated by a priming dose of PE followed by provision of DHP as a maturation inducing hormone.

Low Oxygen Stress During Early Development Influences Regulation of Hypoxia-Response Genes in Farmed Atlantic Salmon ().

Survival and growth of developing salmonids are negatively affected by low oxygen levels within gravel nests in natural streams, and hypoxic stress is often experienced by farmed Atlantic salmon () within hatcheries. Exposure to hypoxia during early development may have long-lasting effects by altering epigenetic marks and gene expression in oxygen regulatory pathways. Here, we examine the transcriptomic response to low dissolved oxygen (DO) in post-hatch salmon reared continuously in 30%, 60% or 100% DO from fertilization until start of feeding.

Cold seawater induces early sexual developmental stages in the BPG axis of European eel males.

Background: The impossibility of closing the life cycle of the European eel (Anguilla anguilla) in captivity troubles the future of this critically endangered species. In addition, the European eel is a highly valued and demanded resource, thus the successful closing of its life cycle would have a substantial economic and ecological impact. With the aim of obtaining the highest gamete quality, the study of the effects of environmental factors, such as temperature, on reproductive performance may prove valuable.

Early Developmental Stress Affects Subsequent Gene Expression Response to an Acute Stress in Atlantic Salmon: An Approach for Creating Robust Fish for Aquaculture?

Stress during early life has potential to program and alter the response to stressful events and metabolism in later life. Repeated short exposure of Atlantic salmon to cold water and air during embryonic (E), post-hatch (PH) or both phases of development (EPH) has been shown to alter the methylome and transcriptome and to affect growth performance during later life compared to untreated controls (CO). The aim of this study was to investigate how the transcriptome of these fish responds to subsequent acute stress at the start feeding stage, and to describe methylation differences that might steer these changes.

Differential expression of gonadotropin and estrogen receptors and oocyte cytology during follicular maturation associated with egg viability in European eel (Anguilla anguilla).

In captivity, oogenesis and ovarian follicle maturation in European eel can be induced experimentally using hormonal therapy. The follicle's ability to respond effectively to the induction of maturation and ovulation, resulting in viable eggs, depends on the oocyte stage at the time of induction. We hypothesized that variation in the expression of key hormone receptors in the ovary and size of oocyte lipid droplets are associated with changes in oocyte stage.

Resolving the complexity of vitellogenins and their receptors in the tetraploid Atlantic salmon (Salmo salar): Ancient origin of the phosvitin-less VtgC in chondrichthyean fishes.

Egg yolk proteins are mainly derived from vitellogenin (Vtg), and serve as essential nutrients during early development in oviparous organisms. Vertebrate Vtgs are predominantly synthesized in the liver of maturing females, and are internalized by the oocyte after binding to specific surface receptors (VtgR). Here, we clarify the evolutionary history of vertebrate Vtgs, including the teleost VtgC, which lacks phosvitin, and investigate the repertoire of Vtgs and VtgRs in the tetraploid Atlantic salmon (Salmo salar).

Impacts of Early Life Stress on the Methylome and Transcriptome of Atlantic Salmon.

Exposure to environmental stressors during early-life stages can change the rate and timing of various developmental processes. Epigenetic marks affecting transcriptional regulation can be altered by such environmental stimuli. To assess how stress might affect the methylome and transcriptome in salmon, fish were treated using cold-shock and air-exposure from the eye-stage until start-feeding.

Multiplicity of Buc copies in Atlantic salmon contrasts with loss of the germ cell determinant in primates, rodents and axolotl.

Background: The primordial germ cells (PGCs) giving rise to gametes are determined by two different mechanisms in vertebrates. While the germ cell fate in mammals and salamanders is induced by zygotic signals, maternally delivered germ cell determinants specify the PGCs in birds, frogs and teleost fish. Assembly of the germ plasm in the oocyte is organized by the single Buc in zebrafish, named Velo1 in Xenopus, and by Oskar in Drosophila.

The expression of nuclear and membrane estrogen receptors in the European eel throughout spermatogenesis.

Estradiol (E) can bind to nuclear estrogen receptors (ESR) or membrane estrogen receptors (GPER). While mammals possess two nuclear ESRs and one membrane GPER, the European eel, like most other teleosts, has three nuclear ESRs and two membrane GPERs, as the result of a teleost specific genome duplication. In the current study, the expression of the three nuclear ESRs (ESR1, ESR2a and ESR2b) and the two membrane GPERs (GPERa and GPERb) in the brain-pituitary-gonad (BPG) axis of the European eel was measured, throughout spermatogenesis.

Interactive effects of dietary composition and hormonal treatment on reproductive development of cultured female European eel, Anguilla anguilla.

Farmed female eels were fed two experimental diets with similar proximate composition but different n-3 polyunsaturated fatty acid (PUFA) levels. Both diets had similar levels of arachidonic acid (ARA), while levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in one diet were approximately 4.5 and 2.

Temperature modulates testis steroidogenesis in European eel.

This study evaluates the effects of temperature on hCG-induced spermatogenesis in European eel (Anguilla anguilla), subjected to three thermal regimes: T10: 10°C (first 4weeks), 15°C (next 3weeks) and 20°C (last 6weeks); T15: 15°C (first 4weeks) and 20°C (last 9weeks); and T20: constant 20°C for the duration of the experiment. At 10°C, maturation stopped in the A spermatogonial stage (SPG1), and no further maturation was observed until the temperature was ≥15°C. With the aim of explaining these results, the influence of temperature on steroidogenic enzyme gene expression and steroid synthesis was tested.

Effect of the probiotic Lactobacillus rhamnosus on the expression of genes involved in European eel spermatogenesis.

Positive effects of probiotics on fish reproduction have been reported in several species. In the present study, 40 male European eels were weekly treated with recombinant hCG for 9 weeks and with three different concentrations (10(3), 10(5), and 10(6) CFU/mL) of probiotic Lactobacillus rhamnosus IMC 501 (Sinbyotec, Italy). The probiotics were daily added to the water from the sixth week of the hCG treatment.

Identification of cortisol metabolites in the bile of Atlantic cod Gadus morhua L.

Interpretation of plasma cortisol levels in wild-caught fish is confounded by the stress of capture. Measurement of cortisol metabolites in fish bile could provide a method for assessing the stress level of wild fish because the time-lag for metabolism, conjugation and excretion into bile avoids the effects of sampling stress. To determine which biliary metabolite(s) to target, four Atlantic cod, Gadus morhua L.

Knockdown of the germ cell factor Dead end induces multiple transcriptional changes in Atlantic cod (Gadus morhua) hatchlings.

The RNA binding protein Dead end (DnD) is essential for maintaining viable germ cells in vertebrates and silencing of the gene has been demonstrated to cause sterility in several mammalian and fish species. Here we investigated transcriptome changes in hatched larvae of Atlantic cod induced by DnD knockdown using morpholino oligonucleotides (MO) injected in two-cell embryos. Whereas no fluorescently labeled germ cells were shown in embryos coinjected with dnd MO and nanos3 3'UTR coupled to green fluorescent protein, DnD knockdown had no visible effect on the number and location of Vasa protein positive cells in larvae.

Conserved mechanisms for germ cell-specific localization of nanos3 transcripts in teleost species with aquaculture significance.

The importance of the aquaculture production is increasing with the declining global fish stocks, but early sexual maturation in several farmed species reduces muscle growth and quality, and escapees could have a negative impact on wild populations. A possible solution to these problems is the production of sterile fish by ablation of the embryonic primordial germ cells (PGCs), a technique developed in zebrafish. Cell-specific regulation of mRNA stability is crucial for proper specification of the germ cell lineage and commonly involves microRNA (miRNA)-mediated degradation of targeted mRNAs in somatic cells.

Divergent and sex-dimorphic expression of the paralogs of the Sox9-Amh-Cyp19a1 regulatory cascade in developing and adult atlantic cod (Gadus morhua L.).

The factors of the Sox9-Amh-Cyp19a1 cascade play a crucial role in the complex process of sex differentiation in mammals. The involvement of Sox9 and Cyp19a1 paralogs and the single Amh ortholog in sex differentiation and development of the gonads and the brain in Atlantic cod was examined by analyzing bimodal and sex-dimorphic gene expression patterns, respectively, during early stages and in maturing males and females. Expression of sox9a and sox9b were initiated at blastulation, and both paralogs were expressed in chondrogenic tissue in the hatched larvae.

Molecular and physiological study of the artificial maturation process in European eel males: from brain to testis.

European eel males can be artificially matured (1.5IU hCG/g fish), but the regulatory mechanisms of their reproductive development are practically unknown. Spermatogenic stages (S1-S6), biometric characters [eye index (EI), gonadosomatic index (GSI), hepatosomatic index (HSI)] and sperm quality parameters (motility, viability and head spermatozoa morphometry) were analysed.

Maternal transfer and transcriptional onset of immune genes during ontogenesis in Atlantic cod.

The immune system in teleosts is not completely developed during embryonic and larval stages and immune competence is assumed to be restricted. This study is the first to address whether immune transcripts are maternally transferred to offspring and when immune genes are transcriptionally active in Atlantic cod (Gadus morhua). In unfertilised eggs, transcripts encoding lysozyme and cathelicidin were found indicating maternal transfer of antibacterial transcripts.

Ontogenesis of catabolic and energy metabolism capacities during the embryonic development of spotted wolffish (Anarhichas minor).

The catabolic and energy metabolism capacities during spotted wolffish (Anarhichas minor) embryogenesis were investigated. We assessed the embryo's ability to catabolize proteins (trypsin-like proteases) and lipids (triglyceride lipase) and examined the development of metabolic capacities using enzymatic assays: ability to use carbohydrates (pyruvate kinase), amino acids (aspartate aminotransferase) and fatty acids (hydroxyacyl-CoA dehydrogenase) for energy production, and aerobic (citrate synthase) and anaerobic (lactate dehydrogenase) energy production. Functional enzymatic systems were detected from the eyed stage (350 degree-days), except for fatty acids, which was detected from 540 degree-days.

Rapid adjustments of sperm characteristics in relation to social status.

Sperm competition models predict that males typically mating in disfavoured roles should be selected to compensate for their disadvantage by investing more into sperm. We studied the effect of rapid changes in social status on ejaculate investments during experimental trials with an externally fertilizing teleost--the Arctic charr (Salvelinus alpinus). We document that males becoming dominant produce less sperm with lower velocity, but have higher sex steroid concentrations than subordinate males.