Gonadotropin expression, pituitary and plasma levels in the reproductive cycle of wild and captive-reared greater amberjack (Seriola dumerili).

We compared the endocrine status of the pituitary-gonad axis of wild and captive-reared greater amberjack (Seriola dumerili) during the reproductive cycle (April - July), reporting on the expression and release of the two gonadotropins for the first time in the Mediterranean Sea. Ovaries from wild females were characterized histologically as DEVELOPING in early May and SPAWNING capable in late May-July, the latter having a 3 to 4-fold higher gonadosomatic index (GSI). SPAWNING capable wild females exhibited an increase in pituitary follicle stimulating hormone (Fsh) content, plasma testosterone (T) and 17,20ß-dihydroxy-4-pregnen-3-one (17,20ß-P), while almost a 10-fold increase was observed in pituitary luteinizing hormone (Lh) content. An increasing trend of plasma 17ß-estradiol (E2) was also recorded between the two reproductive stages in wild females. Captive-reared females sampled during the reproductive cycle exhibited two additional reproductive categories, with REGRESSED females having extensive follicular atresia and fish in the REGENERATING stage having only primary oocytes in their ovaries. Pituitary content of Fsh and Lh, fshb and lhb expression and plasma levels of Fsh and Lh remained unchanged among the four reproductive stages in captive females, in contrast with plasma E2 and T that decreased in the REGENERATING stage, and 17,20ß-P which increased after the DEVELOPING stage. In general, no significant hormonal differences were recorded between captive-reared and wild DEVELOPING females, in contrast to SPAWNING capable females, where pituitary Lh content, plasma Fsh and T were found to be lower in females in captivity. Overall, the captive females lagged behind in reproductive development compared to the wild ones and this was perhaps related to the multiple handling of the sea cages where all the sampled fish were maintained. Between wild males in the DEVELOPING and SPAWNING capable stages, pituitary Lh content, plasma T and 17,20ß-P, and GSI exhibited 3 to 4-fold increases, while an increasing trend of pituitary Fsh content, lhb expression levels and plasma 11-ketotestosterone (11-KT) was also observed, and an opposite trend was observed in plasma Lh. Captive males were allocated to one more category, with REGRESSED individuals having no spermatogenic capacity. During the SPAWNING capable phase, almost all measured parameters were lower in captive males compared to wild ones. More importantly, captive males showed significant differences from their wild counterparts throughout the reproductive season, starting already from the DEVELOPING stage. Therefore, it appears that captivity already exerted negative effects in males prior to the onset of the study and the multiple handling of the cage where sampled fish were reared. Overall, the present study demonstrated that female greater amberjack do undergo full vitellogenesis in captivity, albeit with some dysfunctions that may be related to the husbandry of the experiment, while males, on the other hand, may be more seriously affected by captivity even before the onset of the study.

Timing of puberty in F1-generation hatchery-produced greater amberjack (Seriola dumerili).

We evaluated the onset of puberty of first-generation (F1) hatchery-produced greater amberjack (Seriola dumerili) reared in sea cages for 5 years. Fish were sampled every year in June, at the expected peak of the spawning period in the Mediterranean Sea. No sexual dimorphism in body weight was observed in the study. The ovaries of 1 and 2-year-old (yo) females consisted of primary oocytes only, while at the age of 3-yo early vitellogenic (Vg) oocytes were also identified, but with extensive follicular atresia. At the age of 4-yo, late Vg oocytes were observed, but again extensive follicular atresia characterized the ovaries of 50 % of females. At the age of 5-yo, follicular atresia of Vg oocytes was very limited. In males, gametogenesis was evident already in 1- and 2-yo fish, and 100 % of sampled 3-yo males produced collectable viable sperm. Plasma testosterone (T), 17ß-estradiol (E2), and 17,20ß-dihydroxy-4-pregnen-3-one (17,20ß-P) remained similar in 3 - 5-yo females, with T and E2 levels being highest in females in advanced vitellogenesis or with significant follicular atresia, compared to immature females. In males, plasma T declined over the years, while 11-ketotestosterone (11-KT) and 17,20ß-P were highest in 4 and 5-yo males, with spermatozoa motility characteristics being improved from the 4th year onwards. The administration of GnRHa implants to 5-yo fish induced only two spawns, albeit no fertilized eggs were obtained. The results indicate that hatchery-produced greater amberjack males mature well and within the same age observed in the wild, however with smaller gonad size. On the contrary, females mature later than in the wild, also with a smaller gonad size. Spawning in response to GnRHa treatment was not effective, suggesting that Mediterranean hatchery-produced broodstocks may be dysfunctional, and further research is needed to document any improvement as the fish get older, or to determine if the results may be related to the specific stock of fish.

Sperm quality of greater amberjack Seriola dumerili throughout the reproductive season and in response to GnRHa treatment with controlled release implants.

A wild-caught stock of greater amberjack Seriola dumerili reared in sea cages in two commercial aquaculture facilities in Greece was administered gonadotropin-releasing hormone agonist (GnRHa), loaded in controlled release implants, and was used in spawning induction experiments throughout the reproductive season. Sperm quality was evaluated using computer-assisted sperm analysis (CASA) before and after GnRHa administration and the extent of the spermiation period was determined. Males were in spermiation throughout the monitoring period from May 30 until July 18, at temperatures between 19 and 24 °C. However, lower sperm motility duration, density, and survival under cold storage were observed from early July onwards. Sperm quality did not recover after the end of spawning induction experiments in tanks and the return of the fish for 14-28 days to the sea cage in mid-July, which could be related to the high temperatures of this period. An improvement trend was observed in the quality of the milt collected on day 7 after a single GnRHa administration, but a significant decrease was observed on day 21 in sperm density, survival under cold storage, and straight line velocity (VSL). On the contrary, a double GnRHa administration spaced 14 days apart maintained the same sperm quality for a longer period of 29 days. Further spermiation enhancement experiments should be conducted in the future to describe in more detail the kinetics of sperm production after GnRHa therapy and its effects on sperm quality.

Endocrine regulation of long-term enhancement of spermiation in meagre (Argyrosomus regius) with GnRHa controlled-delivery systems.

Meagre (Argyrosomus regius) undergo spermatogenesis and spermiation when reared in captivity, but often produce low milt volumes, sometimes with reduced quality and for a limited time period. In the present study we a) compared the efficiency of gonadotropin releasing hormone agonist (GnRHa) implants versus injections on testicular stimulation and spermiation enhancement, b) investigated the effect of GnRHa on the endocrine spermiation regulation (sex steroid hormones), and c) evaluated a commercial induced spawning simulation scenario. Firstly, males (n = 5) were injected with 15.0 ± 0.2 µg GnRHa kg-1 (Injections) or implanted with 51.0 ± 5.1 µg GnRHa kg-1 (Implant) and compared their sperm production response. Secondly, the best hormonal treatment (Implant) was tested treating males (n = 8) with 57.5 ± 7.5 µg GnRHa kg-1 every 3 weeks for a period of 70 days. Milt production was improved by the GnRHa implants with only minor sperm quality alterations (improved sperm motility percentage). Elevated plasma testosterone (T) and 11-ketotestosterone (11-KT) levels were recorded in response to GnRHa implants, while no significant difference for 17,20ß-dihydroxy-4-pregnen-3-one (17,20ß-P) was observed. In the commercial induced spawning simulation, it was shown that meagre females are capable of on-demand induction of spawning at random intervals (5-21 days) using GnRHa injections, over a period of at least 2.5 months. During this period, spermiation enhancement was achieved with GnRHa implants every 3 weeks, producing sperm with stable, in general, quality and motility parameters. Percentage of motile cells, motility duration and density fluctuated significantly, but remained within levels that are considered appropriate for high fertilization success in this species.

Effects of Dietary Bisphenol A on the Reproductive Function of Gilthead Sea Bream (Sparus aurata) Testes.

Bisphenol A (BPA), a known endocrine disrupting chemical (EDC), was administered by diet to gilthead sea bream (Sparus aurata) in order to study its effects on the endocannabinoid system (ECS) and gonadal steroidogenesis. 2-year-old male gilthead sea bream were fed with two different concentrations of BPA (LOW at 4 and HIGH at 4000 µg/kg body weight for 21 days during the reproductive season. Exposure to 4000 µg BPA/kg bw/day (BPA HIGH) reduced sperm motility and altered the straight-line velocity (VSL) and linearity (LIN). Effects on steroidogenesis were evident, with testosterone (T) being up-regulated by both treatments and 11-ketotestosterone (11-KT) down-regulated by BPA HIGH. Plasma levels of 17ß-estradiol (E2) were not affected. The Gonadosomatic Index (GSI) increased in the BPA HIGH group. Interestingly, the levels of endocannabinoids and endocannabinoid-like compounds were significantly reduced after both treatments. Unpredictably, a few changes were noticed in the expression of genes coding for ECS enzymes, while the receptors were up-regulated depending on the BPA dose. Reproductive markers in testis (leptin receptor (lepr), estrogen receptors (era, erb), progesterone receptors (pr) and the gonadotropin releasing hormone receptor (gnrhr)) were up-regulated. BPA induced the up-regulation of the hepatic genes involved in oogenesis (vitellogenin (vtg) and zona pellucida 1 (zp1)).

Effects of diisononyl phthalate (DiNP) on the endocannabinoid and reproductive systems of male gilthead sea bream (Sparus aurata) during the spawning season.

Diisononyl phthalate (DiNP) is a plasticizer used to improve plastic performance in a large variety of items which has been reported as an endocrine-disrupting chemical (EDC) in several organisms. The endocannabinoid system (ECS) is a cellular signaling system, whose functionality is tightly involved with reproductive function. The aim of the present study was the assessment of the effects of DiNP on the gonadal ECS and on the reproductive function of male gilthead sea bream Sparus aurata, an important marine aquacultured species in Europe, during the reproductive season. Fish were fed for 21 days with two diets contaminated with different nominal concentrations of DiNP (DiNP LOW at 15 µg DiNP kg-1 bw day-1 and DiNP HIGH at 1500 µg DiNP kg-1 bw day-1), based on the tolerable daily intake (TDI) ruled by the European Food Safety Authority for humans. The transcription of several genes related to the ECS was affected by the DiNP. Specifically, DiNP reduced the levels of endocannabinoids and endocannabinoid-like mediators, concomitant with the increase of fatty acid amide hydrolase (FAAH) activity. At the histological level, DiNP LOW induced the highest occurrence of individuals with regressed testes. Steroidogenesis was affected significantly, since plasma 11-ketotestosterone (11-KT), the main active androgen in fish, was significantly decreased by the DiNP HIGH treatment, while plasma 17ß-estradiol (E2) levels were raised, associated with an increase of the gonadosomatic index (GSI). Additionally, the level of testosterone (T) was significantly increased in the DiNP LOW group, however, the same DiNP concentration reduced the levels of 17,20ß-dihydroxy-4-pregnen-3-one (17,20ß-P). The production of sperm was in general not affected, since spermiation index, sperm density, survival and the duration of forward motility did not exhibit any changes compared to controls. However, computer-assisted sperm analysis (CASA) showed that DiNP reduced the percentage of motile cells. The results clearly suggest a negative effect of DiNP via the diet on the male endocrine system of gilthead sea bream during the reproductive season.

Spawning kinetics and egg/larval quality of greater amberjack (Seriola dumerili) in response to multiple GnRHa injections or implants.

The greater amberjack (Seriola dumerili) is one of the most promising finfish species for aquaculture, due to its cosmopolitan distribution and acceptability, high growth rates and large size. However, lack of reproduction control has been one of the main bottlenecks for its commercialization. The study examined two endocrine methods for the induction of oocyte maturation/ovulation and spawning, which are based on the induction of endogenous Luteinizing Hormone (LH) release from the pituitary, through the use of Gonadotropin Releasing Hormone agonist (GnRHa) either in the form of sustained-release delivery systems (implants) or injections (acute release). The stock (n = 28) consisted of wild fish captured in 2011 and each GnRHa administration method was conducted in two replicates, with 6 and 8 fish per tank, respectively, at a 1:1 sex ratio. Fish were given a GnRHa injection once a week (three administrations), or a GnRHa implant every 2 weeks (two administrations). Mean daily relative fecundity was significantly higher (t1.3 = -5.24, P = 0.012) in the implanted fish (15,170 ±â€¯2,738 eggs kg-1 female day-1) compared to the injected fish (6,119 ±â€¯2,790 eggs kg-1 female day-1). Total relative fecundity was also significantly higher (t1.3 = -9.93, P = 0.003) in the implanted fish (102,402 ±â€¯20,337 eggs kg-1 female) compared to the injected ones (26,517 ±â€¯9,938 eggs kg-1 female), but there were no differences in the quality of eggs in terms of fertilization, 24-h embryo survival, hatching and 5-d larval survival. The number of females with fully vitellogenic oocytes eligible for induction of spawning decreased from the initial to the final sampling, from 7 to 6 females for the GnRHa implant treatment and from 7 to 3 females for the GnRHa injection treatment. In addition to apparently promoting the proper endocrine changes leading to multiple cycles of oocyte maturation, ovulation and spawning, and thus producing larger numbers of eggs; the use of GnRHa implants may be more appropriate in greater amberjack than multiple injections because (a) it also stimulates vitellogenesis and (b) involves less handling of the fish.

Comparative Study of Reproductive Development in Wild and Captive-Reared Greater Amberjack Seriola dumerili (Risso, 1810).

The greater amberjack Seriola dumerili is a large teleost fish with rapid growth and excellent flesh quality, whose domestication represents an ambitious challenge for aquaculture. The occurrence of reproductive dysfunctions in greater amberjack reared in captivity was investigated by comparing reproductive development of wild and captive-reared individuals. Wild and captive-reared breeders were sampled in the Mediterranean Sea during three different phases of the reproductive cycle: early gametogenesis (EARLY, late April-early May), advanced gametogenesis (ADVANCED, late May-early June) and spawning (SPAWNING, late June-July). Fish reproductive state was evaluated using the gonado-somatic index (GSI), histological analysis of the gonads and determination of sex steroid levels in the plasma, and correlated with leptin expression in the liver and gonad biochemical composition. The GSI and sex steroid levels were lower in captive-reared than in wild fish. During the ADVANCED period, when the wild greater amberjack breeders were already in spawning condition, ovaries of captive-reared breeders showed extensive atresia of late vitellogenic oocytes and spermatogenic activity ceased in the testes of half of the examined males. During the SPAWNING period, all captive-reared fish had regressed gonads, while wild breeders still displayed reproductive activity. Liver leptin expression and gonad proximate composition of wild and captive greater amberjack were similar. However, the gonads of captive-reared fish showed different total polar lipid contents, as well as specific lipid classes and fatty acid profiles with respect to wild individuals. This study underlines the need for an improvement in rearing technology for this species, which should include minimum handling during the reproductive season and the formulation of a specific diet to overcome the observed gonadal decrements of phospholipids, DHA (22:6n-3) and ARA (20:4n-6), compared to wild breeders.

Costs of migratory decisions: A comparison across eight white stork populations.

Annual migratory movements can range from a few tens to thousands of kilometers, creating unique energetic requirements for each specific species and journey. Even within the same species, migration costs can vary largely because of flexible, opportunistic life history strategies. We uncover the large extent of variation in the lifetime migratory decisions of young white storks originating from eight populations. Not only did juvenile storks differ in their geographically distinct wintering locations, their diverse migration patterns also affected the amount of energy individuals invested for locomotion during the first months of their life. Overwintering in areas with higher human population reduced the stork's overall energy expenditure because of shorter daily foraging trips, closer wintering grounds, or a complete suppression of migration. Because migrants can change ecological processes in several distinct communities simultaneously, understanding their life history decisions helps not only to protect migratory species but also to conserve stable ecosystems.