Endocrine manipulations of spawning in cultured fish: from hormones to genes

http://digital.csic.es/bitstream/10261/44729/1/Taranger%20et%20al_%2c%20GCE.pdf

Control of puberty in farmed fish

Neurohormones similar to those of mammals are carried in fish by hypothalamic nerve fibers to regulate directly follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin-releasing hormone (GnRH) stimulates the secretion of FSH and LH and the expression of the glycoprotein hormone alpha (GPalpha), FSHbeta, and LHbeta, as well as their secretion. Its signal transduction leading to LH release is similar to that in mammals although the involvement of cyclic AMP-protein kinase A (cAMP-PKA) cannot be ruled out. Dopamine (DA) acting through DA D2 type receptors may inhibit LH release, but not that of FSH, at sites distal to activation of protein kinase C (PKC) and PKA. GnRH increases the steady-state levels of GPalpha, LHbeta, and FSHbeta mRNAs. Pituitary adenylate cyclase-activating polypeptide (PACAP) 38 and neuropeptide Y (NPY) potentiate GnRH effect on gonadotropic cells, and also act directly on the pituitary cells. Whereas PACAP increases all three subunit mRNAs, NPY has no effect on that of FSHbeta. The effect of these peptides on the expression of the gonadotropin subunit genes is transduced differentially; GnRH regulates GPalpha and LHbeta via PKC-ERK and PKA-ERK cascades, while affecting the FSHbeta transcript through a PKA-dependent but ERK-independent cascade. The signals of both NPY and PACAP are transduced via PKC and PKA, each converging at the ERK level. NPY regulates only GPalpha- and LHbeta-subunit genes whereas PACAP regulates the FSHbeta subunit as well. Like those of the mammalian counterparts, the coho salmon LHbeta gene promoter is driven by a strong proximal tripartite element to which three different transcription factors bind. These include Sf-1 and Pitx-1 as in mammals, but the function of the Egr-1 appears to have been replaced by the estrogen receptor (ER). The GnRH responsive region in tilapia FSHbeta 5' flanking region spans the canonical AP1 and CRE motifs implicating both elements in conferring GnRH responsiveness. Generally, high levels of gonadal steroids are associated with high LHbeta transcript levels whereas those of FSHbeta are reduced when pituitary cells are exposed to high steroid levels. Gonadal or hypophyseal activin also participate in the regulation of FSHbeta and LHbeta mRNA levels. However, gonadal effects are dependent on the gender and stage of maturity of the fish.

Regulation of fish gonadotropins.

RIAs were developed for the two salmon gonadotropins (GTH I and GTH II) and used to measure plasma GTH throughout the life of the rainbow trout, Oncorhynchus mykiss. The RIA for GTH II was specific and sensitive (< 0.001% cross-reaction with GTH I, mean sensitivity = 0.26 0.02 ng/ml). The RIA for GTH I was less specific and less sensitive than the GTH II RIA (9.7% cross-reaction with GTH II, mean sensitivity = 2.34 ± 0.23 ng/ml). In both males and females, the levels of GTH II remained undetectable (< 0.3 ng/ml) throughout most of the reproductive cycle, until shortly preceding spermiation/ovulation, when they began to rise. Concentrations of plasma GTH II were maximal at spermiation/ovulation. In both sexes, plasma profiles of GTH I differed from those of GTH II. The plasma GTH I concentration in females was elevated during early vitellogenesis. It then fell to a basal level shortly before ovulation and finally was elevated again at ovulation. In males, increases in plasma GTH I were seen a year before spermiation and again later, during the final stages of testicular growth. These results support the contention that GTH I mediates gonadal growth, whereas GTH II regulates the final stages of maturation and ovulation/spermiation. In rainbow trout, plasma profiles of GTH I and GTH II mimic the cycles of plasma FSH and LH, respectively, in the ovulatory cycle of higher vertebrates.

/pdf/validation-of-radioimmunoassays-for-two-salmon-gonadotropins-3ppoi7zi2t.pdf

Validation of radioimmunoassays for two salmon gonadotropins (GTH I and GTH II) and their plasma concentrations throughout the reproductivecycle in male and female rainbow trout (Oncorhynchus mykiss).

The European eel (Anguilla anguilla Linnaeus 1758) is a species typical for waters of Western Europe. Thanks to early expeditions on the Atlantic Ocean by the Danish biologist Johannes Schmidt who found small (<10mm) leptocephali larvae in the Sargasso Sea about 100 years ago, we have now a strong indication where the spawning site for this species is located. The American eel (Anguilla rostrata, LeSueur) also spawns in the Sargasso Sea. The spawning time and location of both species have been supported and refined in recent analyses of the available historical data. Subsequent ichthyoplankton surveys conducted by McCleave (USA) and Tesch (Germany) in the 1980s indicated an increase in the number of leptocephali <10 mm , confirming and refining the Sargasso Sea theory of Johannes Schmidt. Distinctions between the European and American eel are based on morphological characteristics (number of vertebrae) as well as molecular markers (allozymes, mitochondrial DNA and anonymous genomic-DNA. Although recognised as two distinct species, it remains unclear which mechanisms play a role in species separation during larval drift, and what orientation mechanism eels use during migration in the open sea. The current status of knowledge on these issues will be presented. The hypothesis that all European eel migrate to the Sargasso Sea for reproduction and comprise a single randomly mating population, the so called panmixia theory, was until recently broadly accepted. However, based on field observations, morphological parameters and molecular studies there are some indications that Schmidt’s claim of complete homogeneity of the European eel population and a unique spawning location may be an overstatement. Recent molecular work on European eel indicated a genetic mosaic consisting of several isolated groups, leading to a rejection of the panmixia theory. Nevertheless, the latest extensive genetic survey indicated that the geographical component of genetic structure lacked temporal stability, emphasising the need for temporal replication in the study of highly vagile marine species. Induced spawning of hormone treated eels in the aquarium was collective and simultaneous. In this work for the first time group spawning behaviour has ever been observed and recorded in eels. Studies in swim-tunnels indicate that eels can swim four to six times more efficiently than non-anguilliform fish such as trout. After a laboratory swim trial of eels over 5,500 km, the body composition did not change and fat, protein and carbohydrate were used in the same proportion. This study demonstrated for the first time that European eel are physiologically able of reaching the Sargasso Sea without feeding. Based on catches of newly hatched larvae, temperature preference tests and telemetry tracking of mature hormone treated animals, it can be hypothesised that spawning in the Sargasso Sea is collective and simultaneous, while presumably taking place in the upper 200 m of the ocean. Successful satellite tracking of longfin female eels in New Zealand has been performed to monitor migration pathways. Implementation of this new technology is possible in this species because it is three times larger than the European eel. In the future, miniaturisation of tagging technology may allow European eels to be tracked in time by satellite. The most interesting potential contribution of telemetry tracking of silver eels is additional knowledge about migration routes, rates, and depths. In combination with catches of larvae in the Sargasso Sea, it may elucidate the precise spawning locations of different eel species or groups. Only then, we will be able to define sustainable management issues by integrating this novel knowledge into spawners escapement and juvenile fishing quota.

http://www.bluegreentechnologies.nl/wp-content/uploads/2014/11/25_ginneken.pdf

The European eel ( Anguilla anguilla , Linnaeus), its Lifecycle, Evolution and Reproduction: A Literature Review

Repeated injections of salmon pituitary extract (20 mg per fish per week) induced vitellogenesis in feminized, cultivated Japanese eels (Anguilla japonica). Oocytes were attained at the migratory nucleus stage after 11 or 12 injections. Addition of 17,20β-dihydroxy-4-pregnen-3-one (DHP) into the incubation medium induced germinal vesicle breakdown (GVBD) in the oocytes at the migratory nucleus stage. An injection of DHP (2 µg g-1 BW), given 24h after an injection of salmon pituitary extract (20 mg fish-1), succeeded in inducing maturation and ovulation in females which contained occytes at the migratory nucleus stage. Most fish ovulated 15–18h following the DHP injection. Eggs that were ovulated within 15h after the DHP injection showed high fertility and hatchability, but eggs ovulated 18 or 21h after the DHP injection, showed considerably lower fertility and hatchability. A delay between ovulation and stripping of the eggs rapidly decreased both the fertility and hatchability within 6–9h after ovulation, indicating that artificial fertilization must be carried out immediately after ovulation. Repeated injections of human chorionic gonadotropin (hCG) at a concentration of 1 IU g-1 BW week-1 induced spermatogenesis, spermiation, and the acquisition of potential for sperm motility in cultivated males. Most males spermiated after the fifth or sixth injection of hCG, and the milt weight gradually increased and remained constant (1–2 g) from the 11th to 31th injection. Sperm motility peaked 24h after each weekly injection, and decreased from the 3rd day after the injection. Potassium ions are an essential constituent for the maintenance of motility in the eel spermatozoa. Artificial seminal plasma containing 15.2 mM KCl is applicable as a milt diluent. Using these techniques developed for female and male eels, we have succeeded in obtaining many fertilized eggs from cultivated eels.

Artificial induction of maturation and fertilization in the Japanese eel, Anguilla japonica

Two gonadotropic glycoproteins (PmGTH I and II) were purified by ion-exchange chromatography, gel filtration and preparative SDS-PAGE, from pituitaries of red seabream, a marine teleost which has an asynchronous-type ovary and spawns almost daily during the spawning season. The glycoproteins were composed of distinct subunits and the molecular weights were estimated to be 32 and 38 kDa for PmGTH I and PmGTH II, respectively. Both PmGTH I and II were active in two homologous bioassays: in vitro oocyte maturation and/or in vitro estradiol-17β production assays. These two GTHs were distinct in electrostatic properties, molecular weight, stability and yields from pituitaries during the spawning season. These properties suggest that PmGTH I and II correspond to salmon GTH I and II, respectively.

Purification of gonadotropins (PmGTH I and II) from red seabream (Pagrus major) and development of a homologous radioimmunoassay for PmGTH II.

Milt Production in the Japanese Eel Anguilla japonica Induced by Repeated Injections of Human Chorionic Gonadotropin

As part of a study on the early life of Japanese eel, the development of the digestive organs was observed during the 13 d after hatching. The digestive tract was formed only at the pharynx at hatc...

Development of digestive organs and feeding ability in larvae of Japanese eel (Anguilla japonica)

Development of maturational competence of oocytes of red seabream, Pagrus major, after human chorionic gonadotropin treatment in vitro requires RNA and protein synthesis.

Keiji Hirose

Papers

Artificial induction of maturation and fertilization in the Japanese eel, Anguilla japonica

Purification of gonadotropins (PmGTH I and II) from red seabream (Pagrus major) and development of a homologous radioimmunoassay for PmGTH II.

Milt Production in the Japanese Eel Anguilla japonica Induced by Repeated Injections of Human Chorionic Gonadotropin

Development of digestive organs and feeding ability in larvae of Japanese eel (Anguilla japonica)

Development of maturational competence of oocytes of red seabream, Pagrus major, after human chorionic gonadotropin treatment in vitro requires RNA and protein synthesis.