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1.
In vivo and in vitro approaches have been used to examine the role of dopamine (DA) as a growth hormone (GH)-releasing factor in the goldfish. DA stimulated GH release from perifused pituitary fragments of goldfish in a dose-dependent manner. The GH-releasing effect of DA was seasonal, being the highest in sexually regressed fish, intermediate in recrudescent fish, and the lowest in sexually mature (prespawning) fish. The GH response to DA was blocked by the D1 antagonist (+)SCH23390, confirming the involvement of D1 receptors in DA-stimulated GH release. In studies using static incubation of pituitary cells, somatostatin, a known physiological GH-release inhibitor in the goldfish, abolished the GH response to DA. Intraperitoneal injection of apomorphine, a non-selective DA agonist, also increased the plasma GH levels and enhanced the linear body growth of goldfish. These results strongly suggest that DA, by acting through DA D1 receptors, functions as a GH-releasing factor in the goldfish.  相似文献   

2.
The effect of various dietary starch to proteins ratios (STA/P) on growth performance, oxidative status and liver enzyme activities involved in intermediary metabolism in juvenile Nile tilapia was evaluated. Four isocaloric‐practical diets (12.73 MJ kg?1 digestible energy) with increasing STA/CP ratios were formulated. These were designated D0 (344 g crude protein (CP) and 163.5 g starch (STA) kg?1), D1 (310 g CP and 243 g STA kg?1), D2 (258 g CP and 322 g STA kg?1) and D3 (214 g CP and 401 g STA kg?1). Each diet was fed to triplicate groups of 60 fish (2.7 g) for 45 days. Compared with the control diet (D0), significantly (P < 0.05) depressed growth and feed efficiency were observed only in the groups fed on diet D3. The activities of hepatic enzymes involved in glycolysis and lipogenesis pathways were significantly enhanced in groups fed on diet D3 compared with other diets. A significant (P < 0.05) increase in catalase activity was detected only in groups fed on diet D3. Similarly, a significant (P < 0.05) enhancement in superoxyde dismutase, glutathione S‐transferases and glutathione peroxidise was observed in groups fed on diets D2 and D3 compared with other diets. Results demonstrate the ability of juvenile Nile tilapia to spare protein by dietary carbohydrate.  相似文献   

3.
In the present study, we examined the long-term effects of environmental salinity, diet (35% and 25% crude protein) and 17-methyltestosterone (MT) on corresponding levels of pituitary and serum growth hormone (GH) and prolactins (tPRL177 and tPRL188) in the tilapia (Oreochromis mossambicus). We observed no discernible patterns in serum GH that would suggest an effect of salinity, diet or MT. However, serum GH levels in all treatments declined at 1 and 3h after first feeding. Serum tPRL177 and tPRL188 were significantly higher in freshwater (FW) than in seawater (SW) and levels were significantly affected by dietary protein. tPRL177 levels were higher in all groups fed a 35% protein diet, but tPRL188 levels were higher only in the groups fed the MT-treated 35% protein diet; only serum tPRL188 levels were affected by MT. Moreover, serum tPRL177 and tPRL188 increased throughout the sampling time-course. Subsequent work using fasted tilapia suggests that first feeding is likely to initiate the post-prandial suppression of serum GH levels. In contrast with the picture observed in blood, pituitary glands of SW animals showed higher levels of GH than FW fish. Pituitary GH was elevated by MT in both FW and SW. We also observed that pituitary tPRL177 and tPRL188 levels were higher in FW fish than in SW fish; tPRL177 and tPRL188 levels were elevated by MT only in FW animals. To assess the somatomedin activity of plasma from FW- and SW-reared tilapia, we measured [35S]-sulfate incorporation into ceratobranchial cartilage explants in vitro. Plasma from SW-adapted tilapia showed greater activity in this assay than plasma from FW-reared tilapia, suggesting that the GH-dependent IGF bioactivity of plasma is higher in SW-reared tilapia. Collectively, these studies suggest that the growth-promoting actions of SW rearing and of MT administration in tilapia may be linked to elevations in GH and/or prolactin (tPRL177 and tPRL188)levels.  相似文献   

4.
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5.
It has been established that secretion of gonadotropin (GtH) and growth hormone (GH) release in goldfish are both stimulated by GtH-releasing hormone (GnRH); in addition GtH secretion is inhibited by dopamine D2 mechanisms. In the present study, depletion of protein kinase C (PKC) in goldfish pituitary cells reduced the GtH and GH responses to GnRH and an activator of PKC in static culture. In perifusion studies, GtH released in response to sGnRH analog was greatly attenuated in PKC-depleted cells, however, hormone responses to forskolin were enhanced. Stimulation of dopamine D2 receptors reduced the GtH, but not the GH, responses elicited by PKC activators. These results indicate that PKC participates in the GtH and GH responses to natural neuroendocrine regulators in the goldfish.
Résumé Il a été établi que chez le poisson rouge, les sécrétions de gonadotropine (GtH) et d'hormone de croissance (GH) sont toutes les deux stimulées par la gonadolibérine (GnRH); de plus, la sécrétion de GtH est inhibée par des mécanismes dopaminergiques de type D2. Dans le présent travail, la déplétion de la teneur en protéine kinase C (PKC) dans des cellules hypophysaires de poisson rouge réduit les résponses en GtH et GH au GnRH et à un activateur de la PKC de cellules maintenues en incubation statique. Dans des cellules maintenues en périfusion et soumises à une déplétion en PKC, la GtH libérée en réponse à un analogue du sGnRH est fortement diminuée, cependent les réponses hormonales à la forskoline sont augmentées. La stimulation des récepteurs dopaminergiques D2 réduit, dans le cas d'action d'activateur de la PKC, la réponse en GtH mais pas en GH. Ces résultats indiquent que la PKC est impliquée dans les mécanismes de régulation de GtH et GH par des facteurs neuroendocriniens naturels.
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6.
This study investigated sunflower seed meal (SSM) as dietary protein replacement of fish meal (FM) for Nile tilapia (Oreochromis niloticus) juveniles (initial mean weight of 19.8 ± 6.3 g) reared in earthen ponds for 210 days. SSM replaced 25%, 50%, 75%, and 100% (i.e., D25, D50, D75, and D100, respectively) of FM in an isonitrogenous and isocaloric diet. The optimum FM replacement level of D25 as predicted by the equation y = 177.5 + 26.5x – 7.9x2 yielded an optimum weight of about 184 g within 100 days. Thus D25 was the most effective SSM level for Nile tilapia growth in earthen ponds. Fish growth declined as SSM exceeded D25. The length-weight relationship (r ≥ 90%) depicted an isometric fish growth. Nutrient utilization parameters were similar in all the diets except for D100. The protein content of fish carcass was highest in the control and D25, while fiber level was highest in D100. Amino acids imbalance and high fiber content could have reduced the fish growth at D50, D75, and D100.  相似文献   

7.
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8.
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9.
The resistance to disease caused by the Aeromonas sobria in three genotypes of tilapia, Nile tilapia (Oreochromis niloticus), blue tilapia (Oreochromis aureus) and their hybrid (female Nile tilapia×male blue tilapia) was studied. Based on comparison of median lethal dose (LD50), functions of nonspecific immunity, including total amount of complements, bactericidal reaction by alternative pathway of complement (C3 shunt), percentage of erythrocyte C3b receptor aggregates, leukocyte phagocytic function, as well as erythrocyte active rosette of T lymphocyte, it is indicated that the hybrid has the highest resistance to the disease caused by A. sobria, while blue tilapia has the lowest resistance.  相似文献   

10.
Profiles of plasma growth hormone (GH) in male tilapia hybrid (Oreochromis niloticus x O. aureus) were measured and compared at different times of the year. The profiles did not appear to be repetitive, however, differences in their nature were observed at the different seasons; the most erratic profiles were seen in the height of the reproductive season (July), while the peaks were more subdued in the spring and disappeared in the autumn. Peaks in male fish were more prominent than in the females when measured in July. Perifused pituitary fragments from fish with a high GSI responded to salmon gonadotropin-releasing hormone (sGnRH) analog (10 nM-1 M), while those from fish with a low GSI barely responded to even the highest dose. Exposure of perifused pituitary fragments from sexually-regressed fish to carp growth hormone-releasing hormone (cGHRH; 0.1 M) or sGnRH (I M) stimulated GH release only after injection of the fish with methyl testosterone (MT; 3 injections of 0.4 mg kg 1). The same MT pretreatment did not alter the response to dopamine (DA; 1 or 10 M). GH pituitary content in MT-treated fish was lower than in control fish, which may be explained by the higher circulating GH levels in these fish, but does not account for the increased response to the releasing hormones. Castration abolished the response of cultured pituitary cells to sGnRH (I fM-100 nM) without altering either their basal rate of secretion or circulating GH levels. Addition of steroids to the culture medium (MT or estradiol at 10 nM for 2 days) enabled a GH response to sGnRH stimulation in cells from sexually regressed fish. Pituitary cells which had not been exposed to steroids failed to respond to sGnRH, although their response to forskolin or TPA was similar to that of steroid-exposed cells. It would appear, therefore, that at least one of the effects of the sex steroids on the response to GnRH is exerted proximally to the formation of cAMP, or PKC, presumably at the level of the receptor. An increase in the number of receptors to the GH-releasing hormones, following steroid exposure, would explain also the changing nature of the GH secretory profile in different stages of the reproductive season.  相似文献   

11.
Aminergic metabolism was studied in discrete brain regions of the postovulated female rainbow trout using a liquid chromatography electrochemical detection method. 3 Methoxytyramine (3MT) was the major dopaminergic catabolite, suggesting that catechol-o-methyl transferase is the main dopamine (DA) catabolic enzyme. Two populations of brain regions were found: one with a high DA content and low 3MT/DA ratio (hypothalamus and telencephalon), suggesting that these regions could present a high density of DA perikarya; the other with a high 3MT/DA ratio (pituitary, preoptic area, myelencephalon and optic tectum) suggesting that these regions could present a high density of DA axonal endings. 5 Hydroxytryptamine (5HT) content differed, but an homogeneous distribution of monoamine oxidase was found in different brain regions. High 5HT content was found in the hypothalamus and telencephalon; 5HT was however not detectable in the pituitary.  相似文献   

12.
Studies in mammals have shown that synthetic Met-enkephalin derivatives, called growth hormone-releasing peptides (GHRPs), stimulate growth hormone (GH) release. In the present study, GHRP-6 action on GH secretion was examined in vivo and in vitro in sexually immature grass carp. GHRP-6 injected intraperitoneally had no influences on serum GH levels in juvenile grass carp. Following intraperitonal injection of GHRP-6 and dopamine (DA) or cysteamine hydrochloride (CSH), alone and in combination into juvenile grass carp, DA and CSH were effective in elevating serum GH levels, but GHRP-6 was not effective in this respect; in addition, the synergistic action of GHRP-6 and DA or CSH on GH secretion was not seen. In this work, we had adapted and validated a perifusion system and a culture system for GH regulation studies. In a perifusion system, GHRP-6 (1000 to 0.1 nM), GHRP-6 (0.1 to 1000 nM), GHRP-6 (1 μM), and Hexarelin (an analog of GHRP, 1 μM) had no action on GH release from juvenile grass carp pituitary fragments or cells. Under static incubation conditions, GHRP-6 was inactive on GH release from juvenile grass carp pituitary fragments after 1 h and 6 h incubation, but human growth hormone-releasing hormone (hGHRH; 1 to 100 nM) as positive control could stimulate GH release in a dose-dependent manner. Furthermore, when GHRP-6 (100 nM) in combination static incubation with neuropeptides [e.g., hGHRH (100 nM), salmon gonadotropin-releasing hormone analogue (sGnRH-A) (100 nM), or D-Ala6,Pro9-NEt-luteinizing hormone-releasing hormone (D-Ala6,Pro9-NEt-LHRH, LHRH-A) (100nM)], GHRP-6 did not strengthen GH secretion actions of neuropeptides, and at the same time neuropeptides also did not modify the effects of GHRP-6 on GH secretion. The present results obtained using in vivo and in vitro techniques adapted for GH regulation studies show that GHRP-6 does not function as a GH-releasing factor in juvenile grass carp as it does in tilapia, amphibians, chickens, and mammals.  相似文献   

13.
为了探讨在古老的软骨硬鳞鱼中促性腺激素(GtH)的双重内分泌调节作用,本实验设计用离体灌流的方法研究促黄体素释放激素类似物(LHRH-A)和多巴胺(DA)对施氏鲟脑垂体碎片分泌GtH的影响。引入10、100和1 000 nmol/L 3个浓度的LHRH-A对施氏鲟脑垂体碎片3次脉冲式刺激实验;每次间隔1 h,持续5 min,研究不同剂量LHRH-A对鲟鱼脑垂体释放GtH的作用;用200 nmol/L DA对施氏鲟脑垂体碎片持续2 h灌流后引入5 min的1 000nmol/L LHRH-A刺激实验,研究DA如何抑制鲟鱼脑垂体释放GtH。每5 min收集一管灌流液,用放射免疫测定法(RIA)检测灌流液中GtH的含量。结果显示,低剂量LHRH-A随着刺激引入脑垂体释放GtH出现波浪式的增加,中、高剂量出现释放延后现象。LHRH-A在10nmol/L到1 000 nmol/L范围内对刺激脑垂体释放GtH没有剂量依存关系。DA对施氏鲟脑垂体碎片GtH的分泌没有显著影响,但是可以抑制LHRH-A引起的GtH分泌,即DA不能抑制施氏鲟GtH的基础分泌,而只能抑制LHRH-A诱导的GtH分泌。研究结果证明,在高等硬骨鱼类中存在的双重神经内分泌调节在古老的鲟鱼中也存在。  相似文献   

14.
Growth hormone plays important roles in various physiological processes such as growth, metabolism, and reproduction. In this study, two cDNAs encoding growth hormone receptor (GHR) were isolated from the liver of zanzibar tilapia (Oreochromis hornornum). The two cDNAs were 2,831 and 2,044 bp in length and named GHR1 and GHR2, respectively. GHR1 and GHR2 shared 57.4% similarity in nucleotide sequences and 33.5% similarity in deduced amino acid sequences. Consequently, it was presumed that they were two different genes. Conserved regions of GHR1 and GHR2 in zanzibar tilapia were different from those of other vertebrates. For example, conserved box2 regions of GHR1 and GHR2 in zanzibar tilapia were, respectively, WVELM and WVEFT, while it was WVEFI for GHRs in other vertebrates. Similar to other fish species, GHR1 and GHR2 were expressed in brain, gill, liver, muscle, spleen, gonad, stomach, kidney, and pituitary in zanzibar tilapia. The expression levels were the highest in liver. Unlike fathead minnow (Pimephales promelas) and mossambique tilapia (O. mossambicus), the expression levels of GHR1 in most female fish tissues were higher than those in male fish. No significant difference in GHR2 expression was found in all the tissues in male and female of zanzibar tilapia. Under fasting condition, the expressions of GHRs and IGF-II were significantly up-regulated (P < 0.05) in liver, while the expression of IGF-I remained stable. This observation would contribute to understanding the evolution of the GHR family in further investigation of growth regulation of zanzibar tilapia.  相似文献   

15.
The mechanisms of pituitary adenylate cyclase activating polypeptide (PACAP) action on goldfish growth hormone (GH) release were investigated by examining GH release responses from dispersed goldfish pituitary cells to a synthetic mammalian (m)PACAP38 peptide. It was established that GH release stimulated by 2-h exposure to mPACAP38 was concentration-dependent, attenuated by the PACAP receptor antagonist mPACAP6–38, and subject to neuroendocrine modulation by somatostatin. Maximal mPACAP38-stimulated GH release was not additive to the responses elicited by either the adenylate cyclase activator forskolin or the cyclic (c)AMP analog 8-bromo-cAMP. The GH responses to mPACAP38, forskolin and 8-bromo-cAMP, either alone or in combination, were abolished by H89, a protein kinase A (PKA) inhibitor. SQ22536, an adenylate cyclase inhibitor, attenuated forskolin- and mPACAP38-stimulated GH release. In contrast, mPACAP38-stimulated GH release were additive to the responses to two protein kinase C (PKC) activators and unaffected by two PKC inhibitors. These results suggest that the stimulatory action of PACAP on GH secretion is mediated through a cAMP- / PKA-dependent mechanism, whereas the involvement of PKC appears unlikely. The ability of mPACAP38 to further enhance maximal GnRH (PKC)-dependent GH release, but not dopamine D1 agonist (PKA)-dependent GH secretion, is consistent with this hypothesis. A possible involvement of Ca2+ in PACAP action is also suggested. Two inhibitors of voltage-sensitive Ca2+ channel reduced the GH responses to mPACAP38 in static incubation; conversely, mPACAP38 increased intracellular [Ca2+] in identified, single goldfish somatotropes.  相似文献   

16.
The physiological response of Mozambique and Nile tilapia transferred from fresh to brackish (15 ppt) water was compared during a one-week time course. Response in the pituitary was measured by the gene expression pattern of prolactin (PRL I), growth hormone (GH), and calcium-sensing receptor (CaSR), while the response in the gills was measured by the gene expression pattern of the prolactin receptor (PRL-R), Na+/K+/2Cl− cotransporter (NKCC) and Na+/Cl− cotransporter (NCC), and by activity and expression of Na+/K+-ATPase (NKA). The time-course curves of plasma osmolality levels indicate a rapid elevation 24 h after transfer, which later decreased and maintained at stable level. PRL I expression decreased in both species, but with stronger response in the Nile tilapia, while no differences were found in the slightly elevated levels of GH mRNA. The branchial response demonstrated a faster up-regulation of NKA and NKCC in the Mozambique tilapia, but similar levels after a week, while Nile tilapia had stronger and constant down-regulation of NCC. The time-course response of the measured osmoregulatory parameters indicate that 24 h after transfer is a critical time point for brackish-water adaptation. The differences in responses to saltwater challenge between Mozambique and Nile tilapia shown in this study may be associated with the differences in saltwater tolerance between these two tilapiine species.  相似文献   

17.
An on-station trial was conducted to evaluate the effect of stocking density of freshwater prawn and addition of different levels of tilapia on production in carbon/nitrogen (C/N) controlled periphyton based system. The experiment had a 2 × 3 factorial design, in which two levels of prawn stocking density (2 and 3 juveniles m? 2) were investigated in 40 m2 earthen ponds with three levels of tilapia density (0, 0.5 and 1 juveniles m? 2). A locally formulated and prepared feed containing 30% crude protein with C/N ratio close to 10 was applied considering the body weight of prawn only. Additionally, tapioca starch was applied to the water column in all ponds to increase C/N ratio from 10 (as in feed) to 20. Increasing stocking density of tilapia decreased the chlorophyll a concentration in water and total nitrogen in sediment, and increased the bottom dissolved oxygen. The concentrations of inorganic nitrogenous species (NH3–N, NO2–N and NO3–N) were low due to maintaining a high C/N ratio (20) in all treatment ponds. Increasing prawn density decreased periphyton biomass (dry matter, ash free dry matter, chlorophyll a) by 3–6% whereas tilapia produced a much stronger effect. Increasing stocking density of freshwater prawn increased the total heterotrophic bacterial (THB) load of water and sediment whereas tilapia addition decreased the THB load of periphyton. Both increasing densities of prawn and tilapia increased the value of FCR. Increasing prawn density increased gross and net prawn production (independent of tilapia density). Adding 0.5 tilapia m? 2 on average reduced prawn production by 12–13%, and tilapia addition at 1 individual m? 2 produced a further 5% reduction (independent of prawn density). The net yield of tilapia was similar between 0.5 and 1 tilapia m? 2 treatments and increased by 8.5% with increasing stocking density of prawn. The combined net yield increased significantly with increasing stocking density of prawn and tilapia addition. The significantly highest benefit cost ratio (BCR) was observed in 0.5 tilapia m? 2 treatment but freshwater prawn density had no effect on it. Therefore, both stocking densities (2 and 3 juveniles m? 2) of prawn with the addition of 0.5 tilapia m? 2 resulted in higher fish production, good environmental condition and economic return and hence, polyculture of prawn and tilapia in C/N controlled periphyton based system is a promising options for ecological and sustainable aquaculture.  相似文献   

18.
Several lines of evidence support the idea that more than one gonadotropin-releasing hormone receptor (GnRH-R) subtype exists to accommodate the presence of multiple GnRH forms seen in vertebrate species. The development of pituitary endocrine cells, GnRH-Rs type IA (GfA), IB (GfB) and type III in the pituitary and their synchronization with the establishment of GnRH1-3 regulatory pathways reflect a neuroendocrine function for the GnRH-Rs. Based on developmental, morphological and biochemical evidence it can be hypothesized that GnRH1 regulates gonadotrophs through GnRH-R type IA, GnRH2 regulates prolactin secretion through GnRH-R type IB and GnRH3 regulates growth hormone secretion through GnRH-R type III. Therefore, the three native GnRH variants in advance teleost like tilapia might have their respective cognate receptors, each being capable of regulating different and, to some degree the same pituitary endocrine cells. In the brain, the expression pattern of GnRH-R type IB and type III parallels the distribution of GnRH2 and GnRH3 fiber network, which suggests their role in neuromodulation and reproductive behavior.  相似文献   

19.
Four experimental diets D1, D2, D3 and D4 having 100, 300, 350 and 400 g protein kg?1 diet, respectively, were prepared. Fingerlings of Labeo rohita (5.45 ± 0.03 g) were fed with different diets following a mixed feeding schedule with the feeding cycle of 28 days that consisted of either 28 days feeding of diet D1 or D2 or 21 days feeding with D1 diet and 7 days with either D3 or D4 diet. Different treatments were T1 (D1 for 28 days), T2 (D2 for 28 days), T3 (D1 for 21 days and D2 for 7 days), T4 (D1 for 21 days and D3 for 7 days) or T5 (D1 for 21 days and D4 for 7 days). Fingerlings were sampled after three feeding cycles (84 days). Higher (P < 0.05) growth performance and protein utilization efficiency were found in the T3 group, which was similar to the T2 group. The blood count, NBT, lysozyme activity, serum parameters and stress indicator parameters also complement for the better immunity in the T2 and T3 groups. Therefore, it could be concluded that fingerlings feeding alternately a low‐protein diet (D1) for 21 days followed by a normal‐protein diet (D2) for 7 days in a cycle of 28 days for 84 days maintained better growth and health status.  相似文献   

20.
This study compares how CO2 narcosis and thermal shock affect the physicochemical aspects of Nile tilapia fillets held frozen (?18°C) for up to 6 months. The characteristics of tilapia fillets subjected to CO2 narcosis were those of higher lightness and whiteness and lower redness. The hardness values of fillets of tilapia subjected to thermal shock were lower than those subjected to CO2 narcosis. During frozen storage to both treatments, the drip loss, denaturation of myosin, and lipid oxidation increased, while fillet water holding capacity and hardness decreased. The physicochemical properties of frozen fillets of tilapia stunned by CO2 narcosis were considered more desirable; therefore, the method can be a potential replacement to thermal shock.  相似文献   

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