Prespawning Phase Research Articles

Water temperature and pH influence olfactory sensitivity to pre-ovulatory and post-ovulatory ovarian pheromones in male Barilius bendelisis.

The attractive response and sexual activity elicited by pre-ovulatory steroid sulphate and post-ovulatory 15K-PGF pheromones are greater in wild caught tubercular males and immature males which express breeding tubercles on the snout (at 12-13 days post androgen implant) than in non-tubercular and non-androgen implanted males of freshwater fish Barilius bendelisis. This shows that circulatory androgens exert an activational effect on olfactory receptors of male fish. Wild caught tubercular males and androgen implanted juvenile males exhibit a high responsiveness to steroid sulphate at the water temperature and pH which fish experience during the pre-spawning phase. The male's sensitivity to 15K-PGF is almost equally high at the water temperature and pH which they experience in wild during the both pre-spawning and spawning periods. This suggests that the differential olfactory sensitivity to the two classes of pheromones in androgen implanted males is due to the varied temperature and pH of water, and that during the breeding season the male's olfactory sensitivity to PGF pheromone is more widespread than to the steroidal pheromone. An increased and decreased olfactory sensitivity in mature males to sex pheromones and L-alanine respectively during the breeding phase is in agreement with the hypothesis that pheromonal stimuli dominate over feeding stimuli to promote spawning success.

Spawning behaviour ofPenaeus(Fenneropenaeus)merguiensisde Man and the effect of light intensity on spawning

An experiment was conducted to investigate the effect of light intensity just prior to and during spawning of Penaeus (Fenneropenaeus) merguiensis de Man in the laboratory. Neither the presence of light nor light intensity (0, 10 and 1100 lux) had a significant effect on the spawning process or hatching rate in P. merguiensis. Difference in the percentage of spawners, percentage of incomplete spawning, fecundity and hatching rate were all insignificant (P > 0.05) among the three light treatments. However, spawning was delayed (up to 21 min on average) under 1100 lux with a high percentage of incomplete spawning, compared with the Control (0 lux). For the first time, spawning behaviour of P. merguiensis was observed and fully described. The spawning process can be divided into four phases: dormant, pre-spawning, spawning and post-spawning by distinct behaviour of prawn broodstock. The dormant phase was characterized by a quiescent and non-feeding period, whereas movement of prawn broodstock was active during the pre-spawning and post-spawning phases. Depending on the individual, spawning was completed within 3-5 min. Prawns often stayed still on the water surface during spawning with occasional manoeuvres to change the position. After a short rest at the termination of the spawning phase, prawn broodstock re-exhibited active movement as in the pre-spawning phase, but showing conspicuous care to the deposited eggs. The role of light in controlling ovarian development and spawning, and the behaviour of prawn broodstock in relation to maximizing fertilization rate are discussed.

Gonadotropin releasing hormone (GnRH) neurones of triploid catfish, Heteropneustes fossilis (Bloch): an immunocytochemical study

Gonadotropin-releasing hormone (GnRH), a regulator of gonadal maturation in vertebrates, is primarily secreted by neurosecretory cells of the pre-optic area (POA) in the forebrain of teleosts. GnRH-immunoreactive (GnRH-ir) cells of this area demonstrate positive correlation in number and size of soma with gonadal maturity and directly innervate the pituitary in most teleosts. Gonadal development in triploid fish remains impaired due to genetic sterility. The gonadal immaturity in triploid fish may be due to low levels of gonadotropin and sex steroids during the vitellogenic phase of reproductive cycle. However, the nature of GnRH-ir cells in triploid fish is not yet known. Triploid catfish ( H. fossilis) showed significant decrease ( P<0.001) in size and number of immunoreactive-GnRH cells of POA and low immunoreactivity in pituitary in comparison to their diploid full-sibs during the late pre-spawning phase of ovarian cycle. This study suggests that low activity of GnRH-cells in triploid may be due to lack of positive feedback stimulation by sex steroids and/or reduced responsiveness of sensory cells to environmental cues required for gonadal maturation in teleosts.

Circadian Variation in Circulating Levels of Melatonin, Testosterone and Estradiol-17β in a Tropical Freshwater Catfish, Clarias batrachus, during Different Phases of the Annual Reproductive Cycle

In the present investigation, daily variations in plasma levels of melatonin, testosterone and estradiol-17β were analysed in the tropical freshwater catfish, Clarias batrachus during early and late-preparatory, pre-spawning, late-spawning and post-spawning phases of its annual reproductive cycle. Plasma melatonin levels exhibited a significant circadian rhythm during all the reproductive phases but peaks were invariably at night. The amplitude of melatonin was high during the early-preparatory phase and low in the pre-spawning phase. Testosterone also displayed significant rhythm during all the studied phases except post spawning phase. Estradiol-17β revealed diurnal rhythm only during preparatory and pre-spawning phases. The peak in the levels of plasma testosterone and estradiol-17β were recorded during the photophase. During the late-preparatory phase, the rhythm of testosterone coincided with the rhythm of estradiol-17β.

Seasonal Changes in β-Endorphin-like Immunoreactivity in the Olfactory System of the Female Catfish, Clarias batrachus (Linn.)

In the olfactory system of the catfish Clarias batrachus, β-endorphin-like immunoreactivity was seen in several olfactory receptor neurons (ORN) and their fiber projections extending caudally over the olfactory nerve to the olfactory bulb (OB). With β-endorphin-like immunoreactivity as a cellular marker, the olfactory system in the female fish was investigated at different stages of its annual reproductive cycle. The reproductive cycle of the fish is divisible into four distinct phases: preparatory (February–April), prespawning (May–June), spawning (July–August), and postspawning (September–January). The gonosomatic index and the immunocytochemical profile of β-endorphin-like immunoreactivity showed distinct changes as the fish progressed from one phase to another. In the preparatory phase, limited immunoreactivity was seen in the periphery of the bulb. However, the immunoreactivity showed a robust increase as the immunolabeled fibers extended progressively deeper into the bulb toward the mitral cell layer during the prespawning and spawning phases. Significant reduction in the immunoreactivity was noticed in the olfactory nerve layer of the fish in the postspawning phase. Several granule cells showed poor to moderate immunoreactivity during the spawning phase, although no immunoreactivity was seen in the inner cell layer during the rest of the year. The β-endorphin-like immunoreactivity in the ORN also showed season-related changes, although these were less distinct. Whereas weak immunoreactivity confined to a few ORN was noticed in the fish collected in the preparatory phase, those in the prespawning phase showed conspicuous augmentation in immunoreactivity. During the spawning phase, the sensory layer of the olfactory epithelium showed reduced, homogenous immunoreactivity. In the postspawning phase, several ORN revealed distinct granular immunoreactivity, suggesting possibilities of de novo synthesis. These annual cyclic changes in the β-endorphin-like immunoreactivity were consistently observed over a 30-month study period that spanned three consecutive spawning phases. The results suggest that the β-endorphin-containing ORN, their fiber projections to the OB, and several granule cells in the inner cell layer may be involved in the processing of reproduction/reproductive behavior-related signals.

Behaviour and success of sneaker males in the sand goby, Pomatoschistus minutus

In this study we investigated in laboratory conditions the presence of alternative reproductive tactics in the sand goby and describe proximate factors affecting their expression and success. We describe the reciprocal interactions of resident males, females, and sneaking males. The pre-spawning phase proved to be important for successful nest intrusions by sneakers. The number of sneakers had no effect on the frequency of successful intrusions. When small males had exclusive access to nest sites, they built a nest and courted females, showing a full behavioural repertoire. The intensity of courtship was, however, strongly positively correlated with body size. Using microsatellite DNA markers we assessed paternity shares of territorial and sneaker males in a subset of all replicates. Following successful nest intrusion sneaker males fertilised 5–10% of the eggs. Our interpretation of the results is that sneaking in the sand goby is a conditional tactic, one that is less successful than the normal nest guarding behaviour, at least for one spawning event.

Castration-induced hyperactivity of seminal vesicle in the catfish Clarias batrachus: a case of paradox and blockade by antiandrogen (cyproterone acetate) treatment.

Castration of the catfish Clarias batrachus in late preparatory-early prespawning phase (April-May) caused time-dependent stimulatory effect on morphology, weight, and in the concentrations of biochemical correlates, such as total proteins, fructose, hexosamines and sialic acid in the seminal vesicle (SV). The peak changes were noticed on week 4 of castration. The hyperactivity was related to augmented production of testosterone by the SV of castrates with the levels significantly high from week 3 onwards. As a result, serum testosterone level fluctuated with a significant decrease in the first and fifth weeks, a significant increase in the third week, and no significant difference in the second and fourth weeks. Serum E2 level decreased significantly throughout. Cyproterone acetate treatment (CA; 1 mg/fish daily for 21 days) from the second day of castration decreased the size and weight of the SV and the concentrations of total proteins, hexosamines, fructose and sialic acid. The antiandrogen treatment did not alter serum testosterone level but the E2 level was significantly decreased. It is concluded that the hypersecretory activity of the SV in castrates is a sequel to local synthesis and action of testosterone and the effect could be prevented by CA by blocking androgen actions.

Plasma levels of Gonadotropin-II and gonadal sex steroids in triploid catfish, Heteropneustes fossilis (Bloch)

Triploid fish have under-developed gonads due to altered reproductive endocrinology. Triploids of Indian catfish (H. fossilis) showed significantly reduced plasma levels of gonadotropin (GtH-II), testosterone (T) and estradiol-17β (E2) than that of diploids throughout the year, except for the resting phase, irrespective of sex. Plasma levels of GtH-II were significantly different (p<0.001) between diploid and triploid fish during preparatory, prespawning and spawning phase. The plasma testosterone contents in triploids were significantly less (p<0.001) than that of diploids, except during the resting phase. Triploid females showed very low titres of estradiol-17β (<1 ng ml−1) throughout the annual reproductive cycle in contrast to highly fluctuating levels in diploid females. Thus, this study for the first time provides information on reduced levels of GtH-II and sex steroids in plasma of male triploid fish and additional information on species-specific alteration of sex hormones in female triploids.

The alteration of γ-aminobutyric acid and glutamate contents in the discrete brain offemale tilapia during certain stages of gonadal cycle

The alteration of γ-aminobutyric acid (GABA) and glutamate (Glu) contents in the discrete brain of female tilapia during the certain stages of gonadal cycle was investigated. Both hypothalamic GABA and Glu showed a significantly higher content in the prespawning female than that in the recrudesced and regressed females, which there was no significant difference. In the different gonadal status of female, both telencephalic GABA and Glu showed a maximal content during the prespawning phase and a minimal content during the recrudesced phase. Neither GABA nor Glu content was altered with the gonadal phases in the optic lobe and cerebellum of female tilapia. These results indicate that the alteration of GABA and Glu contents in the hypothalamus and telencephalon, but neither in the optic lobe nor cerebellum, is consistent with the gonadal cycle.

Annual cyclic variations in some biochemical constituents of seminal vesicle and testis of the catfish Heteropneustes fossilis (Bloch): A study correlating plasma testosterone level

In Heteropneustes fossilis, significant annual variations were observed in seminal vesicle-somatic index (SVSI), gonadosomatic index (GSI), concentrations of total proteins, hexosamines, fructose and glucose in both SV and testis, and in plasma testosterone with high values in late prespawning-early spawning phases (June-July) and low or undetectable levels in resting phase (December-January) except for glucose. There is an inverse relationship between the annual patterns of fructose and glucose with fructose dominant in the prespawning and early spawning phases (June-July), and glucose in the resting phase (November-January). The increase in the concentrations of SV and testicular protein, hexosamine and fructose can be correlated with the increase in testosterone concentration on one hand and with the increase of SVSI and GSI, on the other. The decrease in glucose level in the recrudescent phase may be due to its increased conversion into fructose, the main seminal sugar in this species.

Distribution of γ-aminobutyric acid in catfish ( Heteropneustes fossilis) forebrain in relation to season, ovariectomy and E 2 replacement, and effects of GABA administration on plasma Gonadotropin-II level

In the catfish Heteropneustes fossilis, the hypothalamus and telencephalon showed seasonal variations in γ-aminobutyric acid (GABA) with high levels in prespawning and spawning phases and low levels in preparatory and postspawning phases. Ovariectomy for 4 and 5 weeks reduced significantly the GABA contents only in the hypothalamus. Replacement with E 2 (1 μg/g BW) restored the levels to that of sham ovariectomized or parallel control group. Treatment with GABA (i.p.; 10 or 50 μg/g body weight (BW)) alone did not produce any significant effect on plasma gonadotropin-II (GTH-II) level in any of the seasons. Injection of GABA, but not baclofen (a GABA B agonist), stimulated GTH-II secretion in pimozide or GnRH analogue-pimozide pretreated fish at both 0.5 and 2 h in early prespawning phase except at 0.5 h in the pimozide—GABA (10 μg) group. This stimulatory effect was not evident in other seasons. The results of the present study suggest that Estradiol-17β (E 2) seems to stimulate GABA which may account for its high level in the recrudescent phase. GABA seems to have a permissive role in GTH-II secretion when dopamine receptor function is inhibited.

Activity and expression of aspartate aminotransferase during the reproductive cycle of a fresh water fish, Clarias batrachus

Aspartate amino transferase (AspT; EC: 2.6.1.1) is one of the key enzyme of aspartate malate shuttle and non-essential amino acid metabolism. In order to clarify the change of the activities of both cytosolic (c-) and mitochondrial (m-) AspT isoenzymes during the different reproductive stages of Clarias batrachus, an air-breathing carnivorous freshwater fish, the c- and m- AspT activities were measured spectrophotometrically in liver, heart, kidney, brain and ovary during the pre-spawning, spawning and post-spawning phases of the annual reproductive cycle of this fish. Maximum activities were observed during the spawning phase, followed by pre- and post-spawning phases. The native agarose gel electrophoretic pattern revealed two AspT forms, c-AspT and m-AspT, throughout the pre- to post-spawning phases. However, the spawning phase was marked by the expression of an additional anionic form of c-AspT in all tissues studied. These results indicate a distinct utilization of aspartate particularly in the spawning phase in fish in the central metabolic path via transamination reactions, and suggest a control of the enzyme activity by the expression of the additional c-AspT gene, especially at the spawning phase.

Effects of administration of cyproterone acetate on seminal vesicle and testicular activity, and serum testosterone and estradiol-17-β levels in the catfish Clarias batrachus

Cyproterone acetate (CA) was administered in the catfish Clarias batrachus (BW 60–65 g) in a dose of 1 mg/fish daily for 21 days in the prespawning (June) phase of the reproductive cycle. The treatment caused a marked decrease in the size and weight of both testis and seminal vesicle (SV). Spermatogenesis was retarded, inhibiting the transformation of spermatids into spermatozoa. The SV was greatly regressed; the lobules were small with empty lumina or collapsed and fibrosed together with the interstitium in many areas. The CA treatment decreased significantly the concentrations of total proteins, fructose, hexosamines and sialic acid in both the SV and testis, and serum levels of testosterone and estradiol-17β. The results indicate that the regressive changes in the SV and testis were a sequel to decreased androgen level and blockade of androgen actions by interrupting, most likely, the androgen receptor mechanisms.

Annual and Diurnal Variations in, and Effects of Altered Photoperiod and Temperature, Ovariectomy, and Estradiol-17 β Replacement on Catechol-O-Methyltransferase Level in Brain Regions of the Catfish, Heteropneustes fossilis

The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region-specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E 2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 μg/g doses of E 2, and none at week 2 and 5 of OVX and after 0.5 and 1 μg/g doses of E 2. The season-specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.

Methallibure-induced inhibition of hypothalamo-hypophyseal-ovarian activity in the catfish Heteropneustes fossilis involves changes in hypothalamic monoamine activity

Administration of Methallibure, a non-steroidal gonadotropin (GTH) inhibitor 20 μg g−1 body weight; i.p., daily for 10 days, to prespawning phase female Heteropneustes fossilis inhibited the brain-pituitary-ovarian axis as indicated by significant reductions in plasma and pituitary levels of GTH-II, and plasma levels of 17β-estradiol (E2) and testosterone. Concurrently, the treatment resulted in significant reductions in the hypothalamic content of serotonin, noradrenaline (and adrenaline) that stimulate, and a significant elevation of dopamine that inhibits GTH-II release in this species. Activities of the monoamine degrading enzymes, monoamine oxidase and catechol-O-methyltransferase were significantly increased, while that of the synthesizing enzymes, dopamine-β-hydroxylase and phenylethanolamine-N-methyltransferase were significantly decreased. These results suggest that the mechanism of inhibition of GTH-II secretion includes, among others, differential actions of the drug on hypothalamic monoamine metabolism.

Effect of zinc on maturation and breeding potential of Cyprinus carpio and Cirrhina mrigala

Effects of safe and sublethal concentrations of zinc were observed on ovarian maturation and breeding potential of carps. Exposure of Cyprinus carpio to 56 and 100 μg/L and Cirrhina mrigala to 560 and 1000 μg/L of zinc for 60 days during each of the preparatory and prespawning phases of reproduction revealed concentration dependent decline in gonado‐somatic index, ova diameter and absolute fecundity complemented with decline in total proteins and total lipids in the ovaries. Exposed fishes were also induced to breed except C. carpio exposed to sublethal concentration.

In VitroEffects of γ-Hexachlorocyclohexane onin VitroBiosynthesis and Metabolism of Steroids in GoldfishCarassius auratus

Testicular and ovarian fragments ofCarassius auratus,taken during the reproductively active prespawning phase (June) of its annual reproductive cycle, were incubated with different concentrations (0 mg/ml, 0 ppm; 0.001 mg/ml, 1 ppm; 0.01 mg/ml, 10 ppm; and 0.02 mg/ml, 20 ppm) of γ-hexachlorocyclohexane (γ-HCH) in the presence of either exogenous precursor [3H]-17-hydroxyprogesterone ([3H]17-P) or carp hypophyseal homogenate. The free (unconjugated) and conjugated metabolites (glucuronides and sulfates) of [3H]-17-P [androstenedione (AD), androstenetrione, 17-hydroxyprogesterone, testosterone (T), 11-deoxycortisol (S), 17,20α-dihydroxy-4-pregnen-3-one (17,20αP), 17,20β-dihydroxy-4-pregnen-3-one (17,20βP), 7α-pregnanetetrols (7α-P), and other polar metabolites] were separated by thin-layer chromatography and high-performance liquid chromatography. The endogenous production of unconjugated (free) steroids T, 17,20βP, S, and 11-ketotestosterone (11-KT) in response to γ-HCH were measured by radioimmunoassay. Among thein vitrometabolism of [3H]-17-P, in males, free steroids of AD, T, 17,20αP, S, and polar-free steroids were increased with the decreased yield of 11-KT. Percentage yield of testosterone glucuronide (TG) was increased with highly significant decreased yields of polar glucuronide steroids. The sulfate steroids of 17,20αP, 17,20βP, S, and 11-KT remain unchanged. In females, the decreased percentage of yield of AD and S and elevated T were noticed. The yield of TG was increased with decreased yield of 7α-P glucuronides. The percentage yield of AD sulfate and sulfate steroids of 17,20αP, 17,20βP, and S were noted to be increased, but the yield for S sulfate was very high. Endogenous production of T was increased in both sexes in the presence of γ-HCH, but 11-KT in male and S in female were depressed. 17,20βP was stimulated at some concentrations in both sexes but levels were very low. Results indicate that γ-HCHin vitroperturbed the steroid biosynthesis during this phase thereby affecting reproductive physiology.

Plasma sex steroid profiles and the seasonal reproductive cycle in male and female winter flounder, Pleuronectes americanus

The pattern of seasonal gonadal development and variations in plasma sex steroids were investigated in adult male and female winter flounder, Pleuronectes americanus (Walbaum), from Conception Bay Newfoundland beginning August 1987 to December 1988. The winter flounder reproductive cycle can be divided into five consecutive phases of relative reproductive activity including: (1) rapid gonadal recrudescence in the fall (August–December); (2) continued slow gondadal growth in females, or maintenance of the well developed gonads in males, during the winter (December–February); (3) a prespawning phase of gonadal maintenance in the spring (March–April); (4) spawning early in the summer (May–June) after the female gonads reach peak weight; and (5) the summer postspawned period (June–August) when the gonads remain regressed. Female gonadal recrudescence in August is characterized by small increases in plasma estrogen levels and recruitment of small oocytes (≥150 μm) into yolk accumulation. For the winter months, estradiol-17 β levels in the plasma remain stable, approximately 15 ng ml-1, until rising again together with testosterone to peak hormone levels just prior to spawning in conjunction with the highest seasonal values for the gonadosomatic index (GSI) and oocyte diameter. After spawning, the ovaries are regressed and sex steroids in the plasma fall to very low levels. Rapid seasonal recrudescence of the gonads in males is evident from rising GSI values, which reach a maximum in October, and from substantial early seasonal increases in plasma testosterone and 11-ketotestosterone. Afterwards, although GSI values subsequently decline presumably reflecting the process of spermiogenesis and/or onset of spermiation in some males, the testes remain relatively well developed with the presence of sperm throughout the spawning season. As the proportion of spermiating males increases, the plasma levels of the androgenic steroid hormones rise to peak circulating levels from April to June. At the end of the summer reproductive season, the testes of post-spawned males become regressed and plasma testosterone and 11-ketotestosterone levels fall, reaching the lowest seasonal values.

A Turnover Study of Hypothalamic Monoamine Oxidase (MAO) and Effects of MAO Inhibition on Gonadotropin Secretion in the Female Catfish, Heteropneustes fossilis

In the present study, the rate constants of degradation ( k) and synthesis (S) and half-life of hypothalamic monoamine oxidase were determined to explain annual variations and biphasic effects of the enzyme to low and high doses of estradiol-17β (E 2) in 3-week ovariectomized Heteropneustes fossilis . In the preparatory phase, the half-life ( t 1/2) of the enzyme was the longest (21.16 days) with low k (0.03275 days -1) and S (0.000845 Units/day) values, suggesting a low turnover of the enzyme. In the prespawning phase the t 1/2 was the shortest (11.65 days) with high k (0.0595 days -1) and S (0.011 Units/day) values. The low and high turnovers of the enzyme, respectively, in these two seasons could be correlated to low and high profiles of plasma E 2 levels. In the resting phase, the values were in between ( t 1/2 = 18.83 days, k = 0.0368 days -1, S = 0.00211 Units/day) but the plasma E 2 level was undetectable. Three weeks of ovariectomy increased the t 1/2 (19.04 days) compared to that of the control (11.61 days) with decreases in both k and S values. The administration of a low dose of E 2 (0.1 μg/g BW) further increased the t 1/2 (19.63 days) over that of the ovariectomized fish with a significant rise in the S value. However, a high dose of E 2 (1.0 μg/g BW) decreased it (13.33 days) by reducing the S and elevating the k values. These results suggest that the stimulatory effect of low doses of E 2 on the enzyme activity is produced by elevating its synthesis rate and the inhibitory effect of high doses of E 2 by simultaneously decreasing the synthesis and increasing the degradation rates of the enzyme. The administration of a single dose (75 mg/kg BW) of pargyline has elevated plasma gonadotropin (GTH) level after 3 and 6 hr and 7 days in the sham-ovariectomized (control), ovariectomized, and ovariectomized low-E 2-dose groups; the peak increase was found at 6 hr. On the contrary, in the ovariectomized high-E 2 group the GTH level was inhibited at 3 and 6 hr postinjection. These changes in the GTH level could be correlated with changes in the profiles of hypothalamic monoamines. The data show that E 2 exerts its feedback regulation of GTH by modifying monoaminergic activity at the level of oxidative deamination.

Changes in Hypothalamic Catecholamines, Dopamine-β-hydroxylase, and Phenylethanolamine- N-methyltransferase in the Catfish Heteropneustes fossilis in Relation to Season, Raised Photoperiod and Temperature, Ovariectomy, and Estradiol-17β Replacement

In Heteropneustes fossilis, contents and turnovers of hypothalamic catecholamines (CA) and activities of dopamine-β-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) showed significant seasonal variations with significantly high day values. The seasonal pattern of dopamine (DA) on one hand and that of noradrenaline (NA) and adrenaline (A) on the other hand showed an inverse relationship, the former decreasing and the latter increasing during the progress of gonadal recrudescence. The DBH and PNMT levels were low in the resting phase and increased to the peak in the prespawning (DBH) and spawning (PNMT) phases. Maintenance of the fish under long photoperiods (16L:8D) and high temperature (28 ± 2°) stimulated the NA and A, and DBH and PNMT activities, and suppressed the DA mechanism, the changes being maximal in the raised temperature groups. In the resting phase (December), ovariectomy (OVX) or estradiol-17β, (E 2) replacement in 4-week ovariectomized fish did not produce any significant effects on the CA and enzyme activities. On the contrary, in the prespawning phase (May), OVX produced differential and biphasic responses on CA and the enzymes. The contents and turnovers of both NA and A increased significantly at 2-5 weeks and decreased in the sixth week. However, the reverse was true for DA. The DBH and PNMT activities (assayed only 3, 4, and 6 weeks after OVX) were elevated significantly in the third and fourth weeks but decreased in the sixth week. Plasma levels of gonadotropin (GTH) increased significantly at all durations of OVX in a bimodal pattern while the E 2 levels decreased consistently. Supplementation with a low dose (0.1 μg/g BW) or E 2 restored the NA and A and enzyme activities while the higher doses (0.5, 1.0, and 5.0 μg/g BW) depleted them. The reverse was true for DA. The low dose of E 2 restored the GTH level while the higher ones inhibited it significantly. These results indicate that both environmental photoperiod and temperature and E 2-negative feedback act on the CA to modulate GTH secretion.