Regulation of LH synthesis and release by GnRH and gonadal steroids in masu salmon

The roles of salmon GnRH (sGnRH) and gonadal steroid hormones in regulation of LH synthesis and release were examined in primary pituitary cell cultures of masu salmon (Oncorhynchus masou). Pituitaries were taken from fish at four reproductive stages: in March (initiation of sexual maturation); May (early maturation); July (pre-spawning); and September (spawning period). Amounts of LHβ subunit mRNA in the pituitary cells were determined by real-time PCR, and LH levels in the medium were determined by RIA. sGnRH and gonadal steroids including estradiol-17β (E2), testosterone (T) and 11-ketotestosterone (11-KT) were added to the cultures to examine their direct effects on LH response. sGnRH had no significant effect on LHβ mRNA levels at any stages, although a stimulatory trend was noted in March. In contrast, E2 and T considerably increased LHβ subunit mRNA levels in March and May during initial stages of maturation, and the effects were less pronounced in July and September. On the other hand, sGnRH stimulated LH release at all stages in the males and the effects were most prominent in July and September. E2 and T also stimulated LH release in July and September, but their effects were weaker than that of sGnRH. The present results indicate that sGnRH and gonadal steroids directly regulate LH synthesis and release in masu salmon pituitary cells: sGnRH mainly stimulates LH release in the late stage of sexual maturation; whereas, E2 and T are effective in stimulating LH synthesis at earlier stages of maturation.     

The Annual Reproductive Cycle of the White Bass Morone chrysops

The gametogenic cycle of the white bass Moronc chrysops was characterized for one year at monthly intervals by measuring circulating levels of the sex steroid hormones testosterone (T) and 11-ketotestosterone (11-KT) in males, and 17β-estradiol (E₂) and T in females. Vitellogenin (VTG), the egg yolk precursor, was also measured in female blood plasma. Gonadal status of individual fish was assessed by histological evaluation, measurement of oocyte diameters, and spermintion response. At the onset of vitellogenesis (October), blood plasma levels of E₂ and T were low, but increased significantly as the spawning period (March-April) approached and oocytes attnined their maximum diameter. All stages of oocyte development were observed in mature females, indicating that the white bass is a multiple-clutch, groupsynchronous spawner. Androgen levels increased in males throughout the reproductive cycle and reached maximal levels during the spawning period. The increase in androgens coincided with sperm production and spermintion in males. The circannual endocrine and gonadal development patterns observed in white bass were similar to those of other members of genus Moronc .     

Influence of estradiol-17β, testosterone, and 11-ketotestosterone on testicular development, serum steroid hormone, and gonadotropin secretion in male red sea bream Pagrus major

ABSTRACT:   In order to investigate the influence of estrogen and androgen on reproductive activities of male teleosts, male red sea bream were implanted with silicone capsules containing estradiol-17β (E2), testosterone (T) or 11-ketotestosterone (11-KT) in immature and early spermatogenic stages. One month after implantation of either E2 or T, the gonadosomatic index decreased in accordance with testicular regression in both stages. Implantation of E2 decreased circulating 11-KT levels but did not affect gonadotropin (GTH) subunits, follicle stimulating hormone-β (FSHβ), luteinizing hormone-β (LHβ), α glycoprotein subunit (αGSU) gene expression, and serum LH levels in both stages. Alternatively, T decreased serum 11-KT and LH levels, and FSHβ and LHβ mRNA levels in the early spermatogenic stage but not in the immature stage. These results suggest E2 may directly inhibit testicular development through the suppression of 11-KT production. Meanwhile, T may decrease serum 11-KT levels through the suppression of FSH and LH secretion, resulting to inhibition of testicular development in the early spermatogenic stage. Treatment with 11-KT did not affect the testis in either stage, whereas 11-KT increased LHβ and αGSU mRNA levels in immature, and decreased FSHβ mRNA levels in the early spermatogenic stage. These results suggest that 11-KT may have different effects on GTH subunit gene expression in each reproductive stage.     

Physiological stress and innate immune response in gilthead sea bream (<Emphasis Type="Italic">Sparus aurata)</Emphasis> and sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>) exposed to combination of trimethoprim and sulfamethoxazole (TMP-SMX)

The purpose of this study was to determine whether gilthead sea bream and sea bass treated with combination of trimethoprim and sulfamethoxazole (TMP-SMX) differed in terms of physiological and innate immune biomarkers. Fish were exposed to TMP-SMX at 40 ppm concentration for 1 h as a prophylactic usage. Plasma cortisol, glucose, electrolytes (Ca, P, Na, K, Cl, and Mg) as well as plasma lysozyme activity, C-reactive protein (CRP), and ceruloplasmin (Cp) were measured soon after treatment and following 24 and 48 h in normal sea water for recovery. Treatment with TMP-SMX in both gilthead sea bream and sea bass led to an increase in plasma cortisol and glucose. Fluctuations in some electrolytes were found after treatment and during recovery period, however, the ratios of monovalent ions in treated sea bream were similar to control. Hematocrit values as well as plasma lysozyme activity in gilthead sea bream and sea bass were not affected by the treatment. CRP in gilthead sea bream and Cp in sea bass responded to the treatment with decreased levels. Both gilthead sea bream and sea bass displayed a rapid physiological stress response and sensitivity to TMP-SMX exposure, which requires more than 48-h period for regaining homeostasis.     

Involvement of sex steroids,luteinizing hormone and thyroid hormones in upstream and downstream swimming behavior of land-locked sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>

The involvement of testosterone (T), estradiol-17β (E₂), 11-ketotestosterone (11-KT), 17,20β-dihydroxy-4-pregnene-3-one (DHP), luteinizing hormone (LH), thyroxine (T₄), and triiodothyronine (T₃) in the regulation of downstream and upstream movement (swimming behavior) was investigated in land-locked sockeye salmon Oncorhynchus nerka, using an artificial raceway. During the downstream migratory period, T implant resulted in high plasma T levels and inhibited the occurrence of downstream swimming behavior (negative rheotaxis) in yearling (1+) immature smolts. In terms of upstream behavior, 2-year-old (2+) males exhibited high plasma T and 11-KT levels, while 2+ females had elevated T and DHP levels. In 1+ immature fish, a T implant induced upstream swimming behavior (positive rheotaxis). In experiments 1 and 3, the plasma T₄ and T₃ levels of non-migrants tended to be higher than those of migrants. In contrast, no marked changes in plasma and pituitary LH were found in both downstream and upstream migrants. These results suggest that sex steroids, such as T, play significant roles in the regulation of downstream and upstream swimming behaviors in land-locked sockeye salmon.     

Development and validation of an enzyme immunoassay for testosterone: Effects of photoperiod on plasma testosterone levels and gonadal development in male sea bass (Dicentrarchus labrax, L.) at puberty

A specific immunoassay was developed for the quantification of testosterone (T) in sea bass plasma. Specific primary antibody against T was produced using an antigen BSA conjugated with T. The enzyme immunoassay (EIA) had a sensitivity of 5–0.009 ng ml^–1 and 6.2% intra-assay variation; inter-assay variation was 9.5% for sea bass plasma. The effects of two different accelerating photoperiod regimes, compressed photoperiod (CO; 6 months), and constant short photoperiod (9L:15D) with a long photoperiod (15L:9D) in March (SLmar), on T plasma levels and sexual maturation were examined during the onset of puberty in male sea bass. Natural photoperiod (NP) and SLmar groups exhibited the highest T values in December (8.69±1.03 and 10.85±1.04 ng ml^–1, respectively). However, SLmar group showed the first significant decrease in T plasma levels in January, two months earlier than the NP group, which presented elevated T levels until February. The CO group displayed two significant T peaks, one in October (8.90±1.60 ng ml^–1) and the other in January (9.60±1.10 ng ml^–1). Gonadosomatic index (GSI) in the NP and SLmar groups displayed the highest values from December to February (>2.5%). However, the SLmar group showed the first significant increase in GSI in November, one month before the controls, indicating a clear advancement of gonadal development with respect to the NP group. In the CO group, a bimodal pattern was observed with two peaks, one in October–November (1.30±0.25%) and the second in March–April (0.97±0.33%) (P<0.05). In NP group, the percentage of running males was about 80% from December to March while the percentage of running males in the SLmar group (70%) lasted only three months (December to February) decreasing (P<0.05) in March. In the CO group, spermiation began in October (60%), decreased during the next months, and increased again in March–April (30%) (P<0.05). These results indicate the advancement of puberty by either one or two months with respect to the control group in the SLmar and CO groups, respectively, and the presence of a second reproductive surge in the CO group. Collectively, these results suggest that exposure of fish to these photoperiod regimes may affect both the time of the onset of puberty and the pattern of gonadal development in prepuberal male sea bass.     

Stress assessment,quality indicators and shelf life of three aquaculture important marine fish,in relation to harvest practices,water temperature and slaughter method

The objective of this study was to evaluate the effect of harvest practices and slaughter method on stress, quality and shelf life of whole fish (gilthead sea bream, European sea bass and red sea bream) towards the development of a humane slaughter practice. The use of hook and line resulted in significantly lower plasma cortisol and glucose in European sea bass and gilthead sea bream. Water temperature at harvest affected significantly the concentrations of stress indicators (plasma cortisol and glucose), mainly in European sea bass and gilthead sea bream. No significant differences were observed between the harvesting methods, regarding fish appearance, microbial spoilage and sensory scoring and subsequently shelf life. However, significantly lower hardness was recorded in fish harvested using the electric stunner, compared to the fish killed with slurry ice of the same harvesting period. Shelf life ranged between 13–18 days for gilthead seabream, 10–16 days for European sea bass and 10–14 days for red sea bream, depending on harvesting period.     

Fertilization strategies for Sea Bass Dicentrarchus labrax (Linnaeus, 1758): effects of pre‐incubation and duration of egg receptivity in seawater

Studying gamete biology can provide important information about a species fertilization strategy as well as their reproductive ecology. Currently, there is a lack of knowledge about how long sea bass Dicentrarchus labrax eggs can remain viable after being activated in seawater. The objectives of this study were to understand the effects of pre‐incubation of fresh and overripe sea bass eggs in seawater and to determine the duration of egg receptivity. Pooled eggs (fresh and overripe) from four females were pre‐incubated in seawater for 0 min (control), 0.5 min, 1 min, 3 min, 10 min and 30 min and then fertilized by pooled sperm from four males. The fresh eggs had a higher fertilization success than overripe eggs. Our results revealed a significant effect of pre‐incubation time for both the fresh (P < 0.01) and overripe eggs (P < 0.01). Fertilization success of eggs significantly declined for both these treatments after 3 min of pre‐incubation, which clearly indicates that sea bass eggs are able to be fertilized by sperm for up to 3 min after release into seawater. This study has particular importance for understanding fertilization strategies, reproductive potential, as well as reproductive ecology of sea bass.     

Circadian melatonin release <Emphasis Type="Italic">in vitro</Emphasis> by European sea bass pineal

Melatonin production by the fish pineal is under the control of photoperiod. In addition, in some fish species pineal melatonin production is self-sustained by an intrapineal circadian pacemaker, not in salmonids, though. The aim of this research was to test melatonin release in vitro by the pineal of sea bass held under LD 12:12 and DD conditions to determine the endogenous nature of melatonin rhythm. Circadian rhythmicity ( = 28.3 h) was found since rhythmic melatonin release persisted on DD.     

Effects of diet and feeding time on daily variations in plasma insulin,hepatic c-AMP and other metabolites in a teleost fish,Dicentrarchus labrax L.

Juvenile sea bass, 1.5 years old, of mixed sex, held on long photoperiods were fed early on the photoperiod and late on the photoperiod, using different diets. Fish fed natural diets showed a daily rhythmicity of plasma insulin, liver c-AMP, plasma glucose, liver glycogen and muscle glycogen content, however, fish fed a commercial diet did not show this daily rhythmicity except for plasma insulin levels. In addition, these fish had significantly lower levels of plasma insulin, liver c-AMP and plasma glycerol than the group fed on the natural diets at similar feeding times. The time of feeding also induced different rhythmicity patterns in hormones and metabolites as well as a significant change in their mean levels. These facts are discussed in relation with the pre-feeding activity and increased appetite exhibited by the fish fed late on the photoperiod and with their implications on fish culture.     

Production and storage of sperm from the black sea bass Centropristis striata L

Black sea bass Centropristis striata L. are protogynous hermaphrodites that develop and spawn as females before changing sex to male. Since all fish eventually become males, determining the relationship between sperm production, sperm quality and seasonal changes in plasma levels of testosterone (T) and 11‐ketotestosterone (11‐KT) could be useful for identifying appropriate males to maintain as broodstock. Milt and blood samples were collected three times during an 8‐week spawning season. Milt volume (3.5±0.76 mL kg^?1), sperm density (3.2 × 10⁸± 0.31 cells mL^?1), sperm production [11 × 10⁸±3.4 cells kg^?1 body weight (BW)] and sperm motility (80±0.6%) were at their highest during the first sampling interval and coincided with the highest 11‐KT levels (1.0± 0.11 ng mL^?1). All of the sperm indices decreased to their lowest levels during the final 3 weeks of the study. Sperm viability was highly correlated (adjusted R²=0.84) with sperm motility. Sperm cryopreserved in modified Mounib's extender (MME) had the highest post‐thaw motility compared with two other extenders. Post‐thaw motility of sperm cryopreserved in MME was not different from fresh after 90 days of storage. There was no difference in fertilization rates between fresh (69±2.4%) and post‐thaw (67±4.1%) sperm samples taken from the same male or among males. These results demonstrate that the quality of black sea bass spermatozoa is higher earlier in the spawning season and that acceptable post‐thaw fertilization rates can be obtained from cryopreserved sperm.     

Role of neuropeptide Y (NPY) in the regulation of reproduction: study based on catfish model

Significance of NPY in the regulation of GnRH–LH axis was evaluated. Considerable NPY immunoreactivity was seen in the components like olfactory system, basal telencephalon, preoptic and tuberal areas, and the pituitary gland that serve as neuroanatomical substrates for processing reproductive information. Close anatomical association as well as colocalizations of NPY and GnRH were seen in the olfactory receptor neurons, olfactory nerve fibers and their terminals in the glomeruli, ganglion cells of nervus terminalis, medial olfactory tracts, fibers in the ventral telencephalon and pituitary. In the pituitary, NPY fibers seem to innervate the GnRH as well as LH cells. Intracranial administration of NPY resulted in significant increase in the GnRH immunoreactivity in all the components of the olfactory system. In the pituitary, NPY augmented the population of GnRH fibers and LH cells. HPLC analysis showed that salmon GnRH content in the olfactory organ, bulb, preoptic area+telencephalon and pituitary was also significantly increased following NPY treatment. NPY may play a role in positive regulation of GnRH throughout the neuraxis and also up-regulate the LH cells in the pituitary.     

花鲈冰藏过程中肌原纤维蛋白生化特性与新鲜度变化的相关性

为研究冰藏期间花鲈鱼片的品质及蛋白质生化特性的变化,通过感官评分、pH、质构、色差、硫代巴比妥酸值(TBA值)、挥发性盐基氮(TVB-N)值、菌落总数(TVC)和肌原纤维蛋白含量、巯基、羰基含量的测定及十二烷基硫酸钠—聚丙烯酰胺凝胶电泳(SDS-PAGE)确定了冰藏花鲈鱼片理化指标变化,并对肌原纤维蛋白生化特性与主要的...     

Protein sparing effect of dietary lipids in common dentex (Dentex dentex): A comparative study with sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

The common dentex (Dentex dentex) is a sparid fish which is considered a suitable candidate for Mediterranean aqua-culture. A seven-weeks feeding trial was conducted over the summer period with common dentex, sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). All three species were fed to visual satiety with two practical diets with varying crude protein and crude fat levels (55 % protein, 9 % lipids; 46 % protein, 17 % lipids). The initial body weights were 8.2, 11.6 and 17.3 g for common dentex, sea bass and sea bream, respectively. In all cases, specific growth rates were not significantly affected by dietary treatment, but they varied among species (sea bass 1.7–1.8 %; sea bream 2.1–2.3 %; common dentex 3.1–3.2 %). When comparisons between fish species were made, we observed that the increase in growth rates was linked to a decrease of the whole body fat content, as a consequence of a greater utilisation of dietary lipids as energy substrates. Furthermore, in common dentex, the 17 % lipid diet was able to improve protein retention, but this diet effect was less significant in sea bream and sea bass. In contrast to sea bream, the 17 % lipid diet did not up-regulate plasma GH levels in common dentex, which provides additional evidence for a more efficient utilisation of dietary lipids.     

Hormone Profiles of Captive Striped Bass Morone saxatilis During Spermiation, and Long-Term Enhancement of Milt Production

Abstract— Plasma profiles of reproductive and thyroid hormones were studied in captive striped bass Morone saxatilis during an 11-wk period encompassing the spawning season, and the effect of a sustained-release gonadotropin-releasing hormone agonist (GnRHa)-delivery system (GnRHa-implant) on milt production was evaluated. The highest percentage of spermiating fish was observed between mid-April and mid-May, and mean total expressible milt ranged from 3.5 to 6.0 mL/kg. Plasma gonadotropin II (GtH II) increased significantly, though inconsistently, during the spermiation period, whereas testosterone and 11-ketotestosterone levels declined continually. Plasma 17,20β-dihydroxy-4-pregnen-3-one and 17,20β,21-dihydroxy-4-pregnen-3-one remained low and unchanged during the peak of the spermiation period, while thyroid hormones were high and fluctuated without exhibiting a trend consistent with spermiation. The observed endocrine profiles suggest that captivity can diminish plasma GtH II and triiodothyronine levels in striped bass. Transfer of spermiating males from large holding tanks to small spawning tanks reduced total expressible milt after 14 d, but treatment with a GnRHa-implant restored milt volume, presumably due to the prolonged elevation of plasma GnRHa and GtH II induced by the GnRHa-implant. Also, treatment with the GnRHa-implant induced a two- to four-fold elevation of expressible milt for at least 20 d compared to control fish, while resulting in only a 5 to 15% decrease in sperm density. It appears that captivity and hatchery operations can diminish milt production in striped bass, and that GnRHa-delivery systems, via sustained elevation of plasma GtH II, can induce long-term enhancement in milt volume without affecting sperm density greatly.     

α‐Tocopherol in weaning diets for European sea bass (Dicentrarchus labrax) improves survival and reduces tissue damage caused by excess dietary DHA contents

The objective of the present study was to investigate the combined effect of several dietary contents of vitamin E and polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (DHA), on growth, survival, biochemical composition and tissue morphology of sea bass along early development. A feeding experiment was conducted in sea bass larvae using five different diets with the same proximate composition and different ratios of DHA concentrated fish oil [10, 30 and 50 g kg^?1 dry weight (DW)] and vitamin E (α‐tocopherol acetate) (1500 and 3000 mg kg^?1 DW). DHA was readily deposited in fish tissues and associated with higher sea bass mortalities probably because of increased peroxidation risks. Besides, the elevation of dietary DHA contents up to 5% severely increased the incidence of muscular lesions and the presence of ceroid pigment within hepatocytes. However, elevation of dietary vitamin E levels markedly reduced the incidence of these symptoms in sea bass, increasing the tissue content in several PUFA and improving growth and stress resistance. Moreover, when sea bass was fed diets containing high vitamin E levels, fish showed a significant improvement in growth when dietary DHA was raised from 1% to 3%. Therefore, in sea bass larvae, a ratio of 30 g kg^?1 DHA and 3000 mg kg^?1 vitamin E seems to be adequate to achieve a good larval performance and to avoid muscular lesions.     

花鲈冷冻精液受精鱼苗与鲜精受精鱼苗的同工酶比较分析

采用水平凝胶电泳技术对花鲈(Lateolabrax maculatus)冷冻精液受精鱼苗与鲜精受精鱼苗进行了同工酶分析。本实验选取肌肉和肝脏两种组织,检测了IDHP、PGM、LDH、GPI、MDH、G3PDH、ME、HK、SOD、G6PD和SDH等11种酶,得到13个位点:IDHP*、PGM-1*、PGM-2*、LDH*、GPI-1*、GPI-2*、MDH*、G3PDH*、ME*、HK*、SOD*、G6PD*和SDH*。结果显示在0.99水平,SDH*和PGM-2*位点在两种受精鱼苗中均表现为多态,多态位点比例均为0.1538;平均预期杂合度分别为0.0460和0.0407,但未观测到杂合子,观测杂合度均为0,遗传偏离指数均为-1;有效等位基因数分别为1.0720和1.0850,花鲈冷冻精液受精鱼苗与鲜精受精鱼苗的遗传相似度为0.9991,遗传距离为0.0010。由此可见,花鲈的冷冻精液受精鱼苗和鲜精受精鱼苗间未出现同工酶水平上的遗传差异,冷冻保存精液完全适用于花鲈育苗生产。     

Effects of Phase-Shifted Photoperiod Regimes on Oocyte Growth and Hormonal Profiles in Female Striped Bass Morone saxatilis

Abstract.— The use of 12–mo long, but phase-shifted advanced and delayed photoperiod cycles in the regulation of the reproductive cycle was investigated in captive-reared female striped bass Morone saxatilis during the 3-yr study in an attempt to control the timing of sexual maturation under simulated photoperiod conditions. Phase-shifted photoperiod cycles did not induce a full shift in oogenesis during the first year cycles, but did in the following years. Spawning time, indicated by maximum oocyte diameters, was advanced up to 4 mo in females maintained under the phase-shifted advanced photoperiod, and delayed up to 4 mo when they exposed to the phase-shifted delayed photoperiod, compared to the natural spawning time in Spring (March-May). Phase-shifted photoperiod regimes shifted the profiles of plasma testosterone (T) and estradiol (E₂), corresponding to the shift of oogenesis in the respective groups. Significant increases in T and E₂ levels occurred during the vitellogenic phase, and these levels peaked before the occurrence of maximum oocyte diameters. The studies demonstrate that phase-shifted photoperiod regimes can be used to control oogenesis, and have implications for ensuring the year-round supply of mature female striped bass, particularly in domesticated striped bass.     

Modulation of the Post-Prandial Plasma Glucose Profile in Juvenile European Sea Bass Dicentrarchus labrax Fed Diets Varying in Starch Complexity

The post-prandial glycemic response of juvenile European sea bass (initial mean weight 10 g) was determined following acclimation to experimental diets that contained a pea seed meal included at two levels. The ingredient provided a source of starch that replaced purified corn starcWyellow dextrin (2:1) in a reference diet based on fishmeal as the main protein component. The total carbohydrate levels amounted to 25% of the dry matter content and contributed (18%) to the overall gross dietary energy value of 20 MJ/kg. After a 12-wk feeding trial, in which the sea bass grew to over 40 g (mean weight), the plasma glucose profile was recorded over a 24-h period (0 h, 1 h, 3 h, 6 h, 9 h, 12 h, and 24 h) following a meal fed to satiation. Results showed that sea bass are able to regulate their glucostatic tolerance to dietary starch, and that the pea seed meal modulated this effect. Peak post-prandial responses varied between 1 to 9 h and were significantly delayed for the reference diet. Efficacy of glucose assimilation improved for the highest level of pea seed meal inclusion (40% by weight). The relevance of carbohydrate complexity with respect to feed formulation and nutritional requirements of sea bass are discussed.     

New perspective to control of tenacibaculosis in sea bass Dicentrarchus labrax L

This work was carried out to investigate the effects of injection of Tenacibaculum maritimum formalin‐killed cells (FKC), extracellular products (ECPs) and crude lipopolysaccharide (LPS) as well as 1% feed supplements of oil extracts of Echinacea purpurea and Origanum vulgare on sea bass immunity improvement to the favour of T. maritimum experimental infection control after 4 weeks of the experiment. Tenacibaculum maritimum isolated from naturally infected sea bass showed brown to yellowish‐brown lesions (sores) on gills, skin and/or fins and identified by different biochemical methods and polymerase chain reaction technique. Immune parameters namely, total protein, globulin and lysozyme activity, as well as the relative level of protection were improved by T. maritimum (FKC), (LPS), (ECPs), O. vulgare and E. purpurea, respectively compared with control. Histopathological examination of T. maritimum naturally infected sea bass indicated many pathological changes in gill, skin and musculatures. Present study could be concluded that application of T. maritimum (FKC), (LPS), (ECPs), O. vulgare or E. purpurea improved sea bass immunity to the favour of disease resistance against T. maritimum. Further investigations on the combination between the previous control methods and the vaccine application methods will be needed.