Effects of pinealectomy on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing activity in Notemigonus crysoleucas

The effects of pinealectomy on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing activity were examined in the cyprinid teleost, Notemigonus crysoleucas, exposed to various photoperiod-temperature regimes. In fish exposed to a long photoperiod-warm temperature regime, pinealectomy resulted in a decrease in gonadal activity, in hypothalamic gonadotropin releasing activity and an increase in pituitary gonadotropin potency. Fewer gonadotrophs were present in the pituitary of sham operated fish than in the pituitary of pinealectomized fish. Ovarian development was more rapid in sham operated than in pinealectomized fish exposed to a long photoperiod–low temperature regime. Pituitary gonadotropin activity was also greater in shams than in pinealectomized fish. A short photoperiod-warm temperature regime retarded ovarian development in N. crysoleucas. Pinealectomy reversed this trend. Gonadotrophs made up a greater area of the pituitary in pinealectomized fish than in shams under these conditions. Gonadotropin potency of the pituitary and hypothalamic gonadotropin releasing activity were also greater in pinealectomized fish than in shams. The area of the pituitary occupied by gonadotrophs was greater in pinealectomized than in sham operated animals maintained on a short photoperiod-low temperature regime. Pituitary gonadotropin activity was also greater in pinealectomized fish as compared to shams. Pituitary gonadotropin potency varies diurnally in animals maintained on both short and long photoperiods; the rhythm of variation differs depending on photoperiod. Pinealectomy alters the diurnal rhythm of pituitary gonadotropin potency in animals exposed to both long and short photoperiods. It is concluded that pinealectomy has a pronounced effect on reproductive activity in N. crysoleucas. The effects of pinealectomy on reproduction vary with photoperiod, but are mediated via the hypothalamus and pituitary. In fish exposed to long daylengths the pineal favours reproductive activity, but the epiphysis retards reproductive processes in animals maintained on short photoperiods.     

Precocious ovarian recrudescence and induced off–season spawning of Heteropneustes fossilis by D-Lys6 salmon gonadotropin releasing hormone analog (sGnRH-A)

The feasibility of photothermal treatment and use of salmon gonadotropin releasing hormone analogue (sGnRH-A) for induced spawning of Heteropneustes fossilis outside the spawning season was investigated. Fish were maintained at 30° C and 14 h light (L)/10 h dark (D) for 60 days between the post-spawning season and preparatory season. Fish attained gonadal maturity 4 months earlier compared to the natural spawning season. Mature fish were induced to spawn by D-Lys⁶ sGnRH-A at a dose of 25 μg kg⁻¹ body weight. The eggs obtained were fertilizable. Injection of D-Lys⁶ sGnRH-A at different time points during the photodiurnal cycle did not influence the latency period and spawning of H. fossilis .     

In vivo and in vitro effects of oestradiol-17β on lipid metabolism in Notemigonus crysoleucas

The effects of oestradiol-17β on the gonosornatic index, liver size, hepatic and body lipid levels in the cyprinid teleost, Notemigonus crysoleucas , were investigated. Administration of oestradiol to female TV. crysoleucas during the gonadal preparatory and prespawning seasons stimulates increases in ovarian size. During the early spawning season oestradiol therapy results in a reduction of ovarian gonosomatic index. Oestrogen treatment of males causes a suppression of testicular growth. In female fish exposed to long (15-5L/8-5D) or intermediate (12L/12D) photoperiods oestradiol increases body fat reserves. At short photoperiods (9L/15D) oestrogen treatment of females results in body fat store depletion Low doses deplete and high doses of oestradiol increase body lipid reserves in male fish. The hepatosomic index increases in both male and female fish following oestrogen treatment. Oestradiol therapy during the gonadal preparatory season, but not during the prespawning season, increases total liver lipids. The in vitro effects of oestradiol on liver lipid and carbohydrate metabolism were also examined. Under the conditions used in these experiments, lipid depletion was observed in liver slices incubated with or without oestradiol. Pretreatment of fish with oestradiol before liver tissue was removed drastically reduced in vitro lipid depletion. Oestradiol retards the gluconeogenesis and glycogenesis seen in liver slices incubated in a hormone-free medium.     

Entrainment of daily serum gonadotropin cycles in the goldfish to photoperiod, feeding, and daily thermocycles

Female fish were kept under 16L:8D/20 degrees C in November and April and the onset of light and/or feeding times were shifted by several hours in the experimental groups. Photoperiod and feeding entrained significant fluctuations in serum gonadotropin hormone (GTH) levels when the onset of light and the first daily feeding were 4 hr apart, but not when they were 10 hr apart. Fish were subjected to 16L:8D for 14-16 days in February, and to either a constant warm (20 degrees C) or a diurnal sinusoidal (12-20 degrees C) temperature regime, the warmth being imposed during photophase or scotophase. While relatively high, uniform serum GTH levels were found throughout the 24-hr period in fish subjected to constant warmth, warm temperature during the day promoted fluctuations in serum GTH levels, and warmth during night resulted in relatively low, uniform serum GTH levels.     

The effects of pinealectomy on pituitary and plasma gonadotropin levels in Carassius auratus exposed to various photoperiod–temperature regimes

The effects of pinealectomy on pituitary and plasma gonadotropin levels and gonadal development in female goldfish exposed to various photoperiod-temperature regimes during different seasons were examined. Pinealectomy during autumn had no effect on either pituitary or plasma hormone levels or gonadal development. When goldfish are pinealectomized in spring and exposed to long photoperiod conditions, the ovaries regress and plasma gonadotropin levels are significantly depressed compared to sham operated animals. Sham operated goldfish exposed to short photoperiod conditions in spring had regressing ovaries whereas pinealectomized animals under this regime either spawned or had ovaries in the late vitellogenic phase. Plasma gonadotropin titres in the pinealectomized group were significantly lower than those of sham operated animals. The pineal can be either stimulatory or inhibitory to gonadal development depending on the photoperiod regime to which the animals are exposed. The pineal apparently influences gonadal activity by modulating gonadotropin secretion. A diurnal variation in plasma gonadotropin levels was also observed in both sham operated and pinealectomized goldfish exposed to a long photoperiod warm-temperature regime in spring.     

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.     

Differential effects of morphine and naltrexone on the in vitro LH secretion from male and female carp pituitary gland

The in vitro effects of morphine (10(-10), 10(-8), 10(-6) or 10(-5) M) or/and naltrexone (10(-6) or 10(-8) M) on LH release from male and female carp (Cyprinus carpio L.) dispersed pituitary cells (obtained from fish at the time of late gonad recrudescence) were investigated. Morphine alone at the lowest tested concentration (10(-10) M) increased LH secretion from the cells of males. On the contrary, in female cell incubations the highest concentrations of morphine (10(-6) or 10(-5) M) significantly lowered LH levels. Naltrexone alone (at both tested concentrations) had no influence on LH secretion, neither in males nor in females. However in the incubations of female cells it antagonised the influence of morphine at 10(-10) or 10(-8) M. In male cell incubations naltrexone abolished the stimulatory action of morphine at 10(-10) M. The results suggest that in the in vitro culture of carp pituitary cells LH secretion is modulated by the opioids which affect the release of this gonadotropin through the typical opioid receptors and that the mu type of these receptors is involved in this process. The effects of opioid agonist and antagonist depend on the stage of gonadal maturity and the sex of fish i.e. the actual level of sex steroids.     

Gonadal stage-dependent effects of gonadal steroids on gonadotropin II secretion in the Atlantic croaker (Micropogonias undulatus).

Involvement of gonadal steroids in the control of gonadotropin II (GTH II) (homologous to LH) secretion was investigated in the Atlantic croaker (Micropogonias undulatus) using gonadectomy (Gx) and steroid replacement paradigms. Gonadectomy in males and females during the late gonadal recrudescence phase elicited significant increases in the gonadotropin response to stimulation by an LHRH analog (LHRHa), without altering basal GTH II secretion. Slow-release silicone elastomer implants of testosterone or estradiol significantly inhibited LHRHa-induced GTH II secretion in gonad-intact and Gx males, and in Gx females, whereas 5alpha-dihydrotestosterone, a nonaromatizable androgen, was ineffective. Pretreatment of fish with an aromatase inhibitor, 1,4, 6-androstatrien-3,17-dione, 2 days before the administration of testosterone implants, completely blocked the negative effect of testosterone on LHRHa-induced GTH II secretion in males, but only partially restored it in females. This suggests that the negative feedback of testosterone in males is primarily mediated by its conversion to estradiol at the level of the hypothalamus and/or pituitary gland, while in females the androgen may also exert a direct inhibitory effect on GTH II secretion, probably mediated via an androgen receptor. In addition, estradiol and testosterone exerted positive effects on basal and LHRHa-induced GTH II secretion during the early-recrudescence phase of the gonadal cycle. The steroids switched to a negative effect on LHRHa-induced GTH II secretion once the fish had fully developed gonads, possibly as a mechanism that prevents a precocious surge in GTH II secretion and final gamete maturation until gametogenesis is complete and the environmental conditions are appropriate for spawning.     

Prolactin replacement fails to inhibit reactivation of gonadotropin secretion in rams treated with melatonin under long days

This study tested the hypothesis that prolactin (PRL) inhibits gonadotropin secretion in rams maintained under long days and that treatment with melatonin (s.c. continuous-release implant; MEL-IMP) reactivates the reproductive axis by suppressing PRL secretion. Adult Soay rams were maintained under long days (16L:8D) and received 1) no further treatment (control, C); 2) MEL-IMP for 16 wk and injections of saline/vehicle for the first 8 wk (M); 3) MEL-IMP for 16 wk and exogenous PRL (s.c. 5 mg ovine PRL 3x daily) for the first 8 wk (M+P). The treatment with melatonin induced a rapid increase in the blood concentrations of FSH and testosterone, rapid growth of the testes, an increase in the frequency of LH pulses, and a decrease in the LH response to N-methyl-D,L-aspartic acid. The concomitant treatment with exogenous PRL had no effect on these reproductive responses but caused a significant delay in the timing of the sexual skin color and growth of the winter pelage. These results do not support the hypothesis and suggest that PRL at physiological long-day concentrations, while being totally ineffective as an inhibitor of gonadotropin secretion, acts in the peripheral tissues and skin to maintain summer characteristics.     

In vitro production of ovarian steroids in yellow perch (Perca flavescens): effects of photothermal manipulation, gonadotropin and phorbol ester

We investigated the capacity of ovaries of yellow perch to produce steroid hormones in vitro and the ovarian response to gonadotropin and phorbol ester during the annual reproductive cycle. The effects of photothermal manipulation on perch gonadal steroidogenesis and its regulation have also been examined. Initially, all females kept indoors were exposed to the same water temperature and photoperiod. By the end of August, following the first sampling, fish were submitted to different photothermal regimes. Group A was maintained under photothermal conditions characteristic for southern Ohio. Group B was submitted to a condensed light/temperature regime designed to accelerate physiological changes that depend on photothermal stimuli. In group A, basal in vitro production of ovarian estradiol (E2) was the highest in October and November, and hCG significantly stimulated E2 secretion during the entire period of vitellogenesis (October-January). In this group, the highest production of basal testosterone (T) was observed before spawning. hCG-stimulated production of T was highest at the beginning of vitellogenesis. Gonadotropin stimulated T production before spawning, a time when gonadotropin was unable to stimulate E2 production. Phorbol ester (PDBu) stimulated E2 and T production during vitellogenesis at the same time points as hCG did (E2: December, January; T: December). hCG-stimulated T production was not mimicked by PDBu in April. Condensing of the photothermal cycle resulted in diminished ovarian production of E2 during vitellogenesis. Moreover, the fish submitted to a condensed photothermal cycle demonstrated augmented T production during the postvitellogenic stage of ovarian development. Ovaries of group B did not respond to PDBu. Generally, the seasonal fluctuations in ovarian capacity to produce E2 and T as well as in gonadal responsiveness to gonadotropin observed in female yellow perch illustrate the dynamic nature of ovarian endocrine function. The lack of response to gonadotropin with regard to E2 production prior to spawning is not due to insensitivity to gonadotropin, but rather due to some deficiency in steroidogenesis (e.g. reduced aromatase activity). It appears also that ovarian steroidogenesis and its regulation are dependent on annual changes of photothermal conditions.     

Behavioural studies on the lesser sandeel Ammodytes marinus (Raitt) III. The effect of temperature on activity and the environmental control of the annual cycle of activity

The behaviour of the lesser sandeel, Ammodytes marinus (Raitt), has been investigated at 5, 10 and 15° C, using a photographic method of recording activity. The activity patterns at 10 and 15° C were very similar, there being a high level of swimming activity during the light period, which fell to a low level at 5° C. It was also lower at 10° C at the end of the experiment than at the beginning and it is suggested that this might have been due to an increase in the fat contents of the fish. The feeding rate of the fish was measured and showed a Q ₁₀ of 2.08 for the temperature range 5–15° C. The annual cycle of activity of A. marinus is discussed in relation to seasonal changes in food availability, light and temperature, and in the fat content of the fish. It is concluded that after spawning in the December–January period the fish remain buried in the sand until April, because of the limiting effect on swimming and feeding activity of the environmental factors in the intervening period. The proportion of fish available for capture at the start of the fishery in April is related mainly to temperature, but food (as measured by numbers of copepods) light intensity and photoperiod are by then increasing rapidly. After July the fishery ceases and it is thought that this is because the fish have entered an overwintering stage, during which they remain buried in the sand. This phase is also thought to be associated with the maturation of the gonads in readiness for the winter spawning. The factors causing the fish to enter this stage are as yet undetermined but may be related to the attainment of a certain level of fat content.     

Gonadal steroids and anterior lobe dynorphin in the male rat

Immunoreactive (ir)-dynorphin levels were measured, and the species characterized by high performance liquid chromatography (HPLC), in the pituitary and hypothalamus of intact and castrate male rats. On HPLC, ir-dynorphin co-eluted with authentic dynorphin A 1-8, dynorphin A 1-17 and dynorphin 1-32 in the hypothalamus and intermediate lobe; in two different reversed phase (RP)-HPLC systems, anterior lobe ir-dynorphin co-eluted uniquely with dynorphin 32 (4K dynorphin). Anterior lobe levels of total ir-dynorphin were significantly lowered 7 days after castration, while HPLC profiles in all tissues remained unchanged. The change in anterior pituitary ir-dynorphin levels was reversed in a dose-related manner by dihydrotestosterone (15-500 micrograms/100 g b. wt/day); estradiol benzoate (3 micrograms/100 g/day) was without effect. The changes on castration and androgen administration suggest that gonadal steroids play a role in the regulation of dynorphin, as well as gonadotrophins and prolactin, within the anterior pituitary gland.     

Effects of photoperiod on pituitary gonadotropin levels in masu salmon

We examined the effects of photoperiod on pituitary levels of two types of gonadotropin (GTH), GTH I and GTH II, in masu salmon Oncorhynchus masou to study their mechanism of synthesis. In Experiment 1, the effects of long or short photoperiod combined with castration were examined using 8-month-old precocious males. Castration was carried out in early August and then the fish were reared under a short (8L16D) or long (16L8D) photoperiod for 60 days. In Experiment 2, the effects of photoperiod combined with testosterone treatment were examined using 12-month-old immature females. Silastic tubes containing testosterone (500 microg /fish) or vehicle were implanted intra-peritoneally in early October. Fish were reared under 16L8D for 60 days, and then half of the fish were transferred to 8L16D, while the remaining fish were kept under 16L8D until Day 90. In Experiment 1, GTH I contents were higher under 16L8D than under 8L16D in the castrated group on Day 30. Moreover, GTH I contents were higher in the castrated group than the control group under 16L8D on Day 30. GTH II contents increased with testicular maturation in the control groups, whereas they remained at low levels in the castrated groups regardless of photoperiodic treatment. In Experiment 2, GTH I contents did not change remarkably in all the groups, while GTH II contents were remarkably increased by testosterone treatment regardless of photoperiodic treatment. These results indicate that the synthesis of GTH I and GTH II are differently regulated by photoperiod and testosterone in masu salmon.     

Effect of phorbol ester on stimulus-secretion coupling mechanisms in gonadotropin releasing hormone-stimulated pituitary gonadotrophs

The feedback regulatory control mechanism exerted by activated Ca2+/phospholipid-dependent protein C kinase upon gonadotropin releasing hormone (GnRH) binding, stimulation of phosphoinositide turnover and gonadotropin secretion was investigated in cultured pituitary cells. Addition of the tumor promoter phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), at concentrations which activate pituitary protein C kinase, to cultured pituitary cells resulted in up-regulation of GnRH receptors (155% at 4 h). The stimulatory effect of GnRH on [3H]inositol phosphates (Ins-P) production in myo-[2-3H]inositol prelabeled pituitary cells was not inhibited by prior treatment of the cells with TPA (10(-9)-10(-7) M). Higher concentrations of TPA (10(-6)-10(-5) M) inhibited the effect of GnRH on [3H]Ins-P production. Increasing concentrations of TPA or the permeable analog of diacylglycerol 1-oleoyl-2-acetylglycerol (OAG) stimulated luteinizing hormone (LH) release from cultured pituitary cells with ED50 values of 5 x 10(-9) M and 10 micrograms/ml, respectively. No consistent inhibition or additivity of LH release was observed when increasing doses of TPA or OAG were added with a submaximal dose of GnRH. These results suggest that protein C kinase might mediate the known homologous up-regulation of GnRH receptors during the reproductive cycle. Protein C kinase is positively involved in mediating the process of gonadotropin secretion. Unlike many other systems, activation of protein C kinase in pituitary gonadotrophs is not involved in negative feed-back regulation of stimulus-secretion-coupling mechanisms in GnRH-stimulated gonadotrophs.     

Triiodothyronine (T3) modulation of gonadotropin secretion in the female rat.

The effect of T3 upon gonadotropin secretion was examined in ovariectomized (Ovarx), Ovarx thyro-parathyroidectomized (Ovarx-TxPx), or proestrus rats. T3 (50 microgram/-100 gBW), administered late diestrus-2, abolished the LH surge during the critical period of proestrus in 7 out of 9 rats; the rise in sera FSH was not inhibited, although a distinct peak was absent. Administration of 5 or 50 microgram T3/100gBW 2.5h before the critical period resulted in either a suppression or an alteration of the timing of LH release. In the 5 microgram T3/100gBW treated animals the sera FSH peak was delayed in timing, whereas in the 50 microgram T3/100gBW treated rats sera FSH demonstrated two separate peaks during the critical period. Treatment with various dosages of T3 of Ovarx-TxPx rats resulted in significant suppressions (p less than 0.05) of sera LH and FSH. Despite depressed concentrations of sera LH and FSH in T3-treated rats pituitary sensitivity to a challenge of 3LHRH was enhanced. Hence, the pituitary was not the site of T3 inhibition of gonadotropin secretion. Additionally, T3 did not modify pituitary LH content or hypothalamic LH3 releasing activity (LHRH). Since T3 did not inhibit gonadotropin secretion at the pituitary level, a neural site of T3 action is suggested.     

Sequence of gonadal events and oestradiol levels in Sparus aurata (L.) under two photoperiod regimes

Individually tagged Sparus aurata were kept in tanks with running sea water (21°± 2°C) during their second and third years of life. Gonads were biopsied and blood was sampled at monthly intervals. Thirteen of 50 fish in the second year and 24 of 35 fish in the third year were phenotypically females. Fish kept under 16L/8D photoperiod from July 1981 to August 1982 did not reach maturation; waves of initial ovarian growth alternated with waves of atresia. When photoperiod was shortened as from August 1982, gonadal development commenced within a month and proceeded at a rate higher than that of the control fish reared under natural photoperiod. Under natural photoperiod oestradiol serum levels (E₂) were relatively low during the resting phase, May-October (108 ± 11 pg ml⁻¹), and during the late vitellogenic phase (502 ± 76 pg ml⁻¹). High levels (1669 ± 312 and 1240 ± 172pg ml⁻¹) occurred during the early vitellogenic and the maturational phases. The high level of E₂ during the spawning season of S. aurata is explained by earlier reports indicating a prolonged breeding season with daily release of eggs, and alternating daily surges of E₂ and 17α, 20β, dihydroxy-4-pregnen-3-one, possibly a 'maturational progestin' in this fish. In phenotypic males, E₂ was highest during early spermatogenic phases (745 ± 142pg ml⁻¹) but was low (155 ± 11 pg ml⁻¹) in males with running sperm.     

The response of trout red cells to adrenaline during seasonal acclimation and changes in temperature

Adult rainbow trout were acclimated to three different temperature and photoperiod regimes: 17°C, 14 h light: 10 h dark (summer); 7° C, 14 h light: 10 h dark; and 5° C, 8 h light: 16 h dark (winter). Blood was collected from these fish after 40 days acclimation, and the response of red blood cells to in vitro adrenergic stimulation was assessed. To examine potential seasonal variations in endogenous levels of circulating catecholamines, plasma levels of adrenaline (Ad) and noradrenaline (NAd) were measured at rest and after exercise. At rest, there were no differences between groups in plasma levels of either Ad or NAd, but, after exercise, the pattern of catecholamine elevation differed. In fish acclimated to 17 and 7° C in summer, Ad and NAd increased by about the same amount (10–15 times). In fish acclimated to 5° C in winter, NAd increased about three-fold, compared to the near 50-fold increase in Ad levels. Whether this difference between groups can be attributed to seasonal influences is unclear. At both low (0·5%) and high (2%) PCO ₂, adrenergic stimulation (2 × 10^-7 M Ad) of trout red cells in vitro led to a significant reduction in MCHC (mean cell [haemoglobin]), compared to non-stimulated cells. However, only at the high PCO ₂ were pHe and red cell pHi significantly different from those in the non-stimulated cells: the latter was higher and the former lower in the stimulated cells. There were no differences in the response of red cells to adrenergic stimulation between groups of fish. Under the conditions of the present study no influence of season and/or temperature on the in vitro response of trout red cells to adrenergic stimulation was shown.     

Spontaneous and gonadotropin-induced ovulation in the goldfish, Carassius auratus L: effects of external factors

Spontaneous ovulation in goldfish is synchronized with photoperiod and influenced by water temperature and aquatic vegetation. As the latency to ovulation from injection of HCG is highly temperature dependent, the finding that ovulation occurs at approximately the same time of day at temperatures from 12° to 26° C suggests the time of the endogenous preovulatory gonadotropin surge may change with the temperature. The time of spontaneous ovulation adjusts to a reversed light:dark cycle within 2 weeks; some 4–6 h shifts in a single light:dark cycle modify the time of ovulation.
Few sexually mature females kept under long photoperiod (16L:8D) and transferred from cold (13 ± 1°C) to warm (21 ± 1°C) water ovulated spontaneously. Exposure to artificial aquatic vegetation for as little as one light phase significantly increases the proportion offish ovulating in warm water. Fish kept in cold water without vegetation do not ovulate; the addition of vegetation induces ovulation, although the response latency is longer than in warm water. Aquatic vegetation may be an effective stimulus for ovulation in other teleosts which spawn on this substrate.     

Circannual rhythms of gonadal maturation in female rainbow trout (Oncorhynchus mykiss).

Individually identified, 2-year-old female rainbow trout were maintained for up to 51 months on a constant schedule of 6 hr light and 18 hr darkness (LD 6:18), constant temperature (8.5-9.0 degrees C), and constant feeding rate. The fish exhibited free-running circannual rhythms of gonadal maturation and ovulation, which were self-sustaining for up to three cycles. The periodicity of the rhythm showed variation between fish and in successive cycles for the same fish, ranging from approximately 11 to 15 months.     

Haematocrit values in feral goldfish, Camssius auratus L., as indicators of the health of the population

Haematocrits were measured in goldfish, Carassius auratus L., collected in early spring and late summer from two locations in southern Ontario, Canada. At one location (Hamilton Harbour) the goldfish population suffered an epizootic of haemorrhagic lesions resulting in chronic anaemia, and at the second location (Cambridge) the goldfish population was disease-free; haematocrits of the feral fish were compared with values obtained from a commercial breeding stock (CBS), and with published haematocrit values for cyprinid fish. Haematocrits in males were larger than in females in all collections of feral fish except spring-caught (7–15°C ambient temperature) fish from Cambridge; no sex differences were evident in the immature CBS fish. Haematocrits were higher in feral female goldfish collected from higher ambient temperatures (15–25°C) than in comparable fish collected from lower ambient temperatures (4–15°C) at both collection sites, and also in males collected from Cambridge. Conversely, the haematocrit in the CBS fish was significantly decreased in fish transferred from 12 to 21°C. Haematocrits of the healthy (Cambridge) population were significantly larger than in comparable fish from Hamilton Harbour.