The entrainment and gating of the endogenous circannual rhythm of reproduction in the female rainbow trout (Salmo gairdneri)

Summary The endogenous circannual rhythm of maturation in the female rainbow trout and associated changes in serum oestradiol-17 and vitellogenin (as calcium) can be entrained by abrupt changes in the photoperiod. Groups of virgin fish (which naturally spawn in December) maintained under LD 186 from mid-January (Year 1), and then subjected to a reduction to LD 618 either on 1st March (Group A), 1st April (Group B), 1st May (Group C) or 1st June (Group D), commenced spawning on 31st July, 13th and 30th August, and the 16th September, respectively. Fish maintained on LD 186 throughout the experiment (Group E) commenced spawning on 10th October. These advances in the timing of spawning can be described in the form of a phase-response curve analogous to the entrainment behaviour of circadian oscillators. It is concluded that under natural conditions the annual change in photoperiod serves to continuously entrain the circannual clock thus ensuring that maturation and spawning occur at the optimal season for the survival of the species.In Groups A, B, C and D, respectively, 74%, 48%, 23% and 8% of the fish failed to mature in Year 1. Maintaining a sample of both maturing and non-maturing trout under constant LD 618 for a further year resulted in all the fish spawning in August of Year 2, approximately one year after the spawning members of this group matured in Year 1. It is proposed that the reduction from LD 186 to LD 618 phase-advanced a circannual timing mechanism in all the fish which then free-ran; this advance was only overtly expressed by the earlier spawning of a certain percentage of the fish in Year 1, but in all the fish in Year 2. These results indicate that the internal timing mechanism can be dissociated from the neuroendocrine mechanisms controlling maturation and thus it can be considered as an autonomous circannual clock. The relationship between the timing of the reduction in photoperiod and the percentage of virgin fish attaining maturation can be explained by a gating model. It is hypothesized that the energetically demanding process of gonadal maturation is only allowed in virgin fish which have reached a certain threshold stage of development and when the clock is at a specific (gate open) phase of the circannual cycle.     

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii

Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause is positively correlated with latitude (r ² = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude, so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14 (T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying circadian pacemaker. Received: 22 July 1996 / Accepted: 30 September 1996     

Photoperiodic response curves for plasma LH concentrations and age at first egg in female broiler breeders

The objective of this work was to define precisely the response curve for photoinduced luteinizing hormone (LH) release in feed-restricted meat-type (broiler) breeder females and to compare it with the photoperiodic response curve for advance in age at first egg (AFE). Birds with a mean body weight of 2.0kg at 20 weeks of age were transferred from an 8 to a 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 14 or 18-h photoperiod; change in plasma LH was measured 4d after photostimulation and subsequent individual AFE recorded. The first significant increase in LH secretion was seen in birds transferred to an 11.5-h photoperiod, but no further significant increases in LH were observed in birds transferred to longer photoperiods. A photoperiodic response curve based on a meta-analysis of changes in photoinduced LH secretion observed in this study and data from an earlier experiment using dwarf broiler breeders indicated a critical daylength of about 9.5h and a saturation daylength of approximately 13h. Similarly, the first significant advance in AFE occurred in birds transferred to an 11-h photoperiod, but with no further significant increases seen in birds transferred to photoperiods >11h. A response curve for photoinduced advances in AFE was produced by meta-analysis using data from the present study and from an earlier investigation involving fewer, more widely spaced photoperiods. It is concluded, in female broiler breeders, that the photoperiodic response curves for photoinduced LH release and AFE are similar, with the point at which the responses begin to rise steeply (classical critical daylength) occurring at 9.5h and the asymptote (classical saturation daylength) at 13h. Functionally, however, the minimum photoperiod to achieve a significant change in either LH secretion or advance in AFE is between 11 and 11.5h.     

Photoperiodic regulation of annual testicular events in the Indian major carp Catla catla

The importance of photoperiods in the regulation of annual testicular events in the carp Catla catla was evaluated by subjecting them to either long (16 h light : 8 h dark) or short (8 h light : 16 h dark) photoperiods for 30 days during the preparatory, prespawning, spawning and postspawning phases of an annual gonadal cycle. In each reproductive phase, testicular responsiveness to subjected photoperiods was determined by comparing the gonadal status in corresponding groups of control or natural photoperiodic fish. The values of testicular weight, gametogenic index, as well as testicular activity of two steroidogenic enzymes (Δ⁵3β‐, and 17β‐hydroxysteroid dehydrogenase), and the serum titre of testosterone were considered as the indices of functional status of the testis in the fish concerned. During the prespawning phase, exposure of fish to a daily long photoperiod schedule resulted in precocious maturation of testis, while retardation of testicular growth was noted under the influences of short photoperiod. However, none of the employed photo‐schedules could influence the gametogenic and steroidogenic functions of the testis in the remaining part of the gonadal cycle. Collectively, the present study provides evidence for the first time that in the case of a commercially important carp, Catla catla, artificial, long photoperiods may be used for advanced testicular maturation, while reductions in maturation‐associated growth and deterioration in flesh quality may be avoided by submitting the fish to shorter day lengths during the prespawning phase of the reproductive cycle.     

Hourglass and rhythmic components of photoperiodic time measurement in the pitcher plant mosquito, Wyeomyia smithii

The mosquito, Wyeomyia smithii, enters a larval dormancy or diapause that is initiated, maintained, and terminated by photoperiod. The median or critical photoperiod regulating diapause increases from 12 h of light per day along the Gulf of Mexico, USA (30° N), to over 15 h in southern Canada (49° N). Photoperiodic time measurement in W. smithii comprises both rhythmic and hourglass (interval timer) components. Using interrupted-night and resonance experiments, we show that both the rhythmic and hourglass components are prominent in the southern (ancestral) populations and that the influence of the rhythmic component declines with increasing latitude, while the hourglass component remains strong in northern (derived) populations. Previously, it has been shown that the genetic differences in critical photoperiod between northern populations and their southern ancestors involve not only the additive (independent) effects of genes, but also gene-gene interaction (epistasis). We therefore conclude that adaptive evolution of W. smithii has probably involved the progressive epistatic masking of the ancestral rhythmic component resulting in photoperiodic time measurement in northern populations accomplished principally through a day-interval timer. A comparison of W. smithii with previous studies indicates that the decline in critical photoperiod with increasing latitude represents an overall decrease in response to light rather than a shift in the timing of photosensitivity among arthropods in general. We propose that the underlying functional components of photoperiodic time measurement, as well as the overt photoperiodic response, are either homologous or are themselves responding directly to selection over latitudinal gradients in seasonality. Received: 18 May 1998 / Accepted: 14 September 1998     

Reduced body mass, food intake, and testis size in response to short photoperiod in adult F344 rats

Background  

Although laboratory rats are often considered classic nonseasonal breeders, peripubertal rats of two inbred strains, F344 and BN, have both reproductive and nonreproductive responses to short photoperiods. Unmanipulated adult rats have not been reported to have robust responses to short photoperiod alone, although several treatments can induce photoperiodic responses in adults. In this study, we tested the hypotheses that unmanipulated F344 rats retain responses to short photoperiod as adults and that they have the necessary elements for an endogenous circannual rhythm of sensitivity to short photoperiod.     

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.     

Microsatellite DNA analysis of rainbow trout (Oncorhynchus mykiss) from western Alberta, Canada: native status and evolutionary distinctiveness of “Athabasca” rainbow trout

Molecular genetic assays can contribute to conservation of aquatic taxa by assessing evolutionary and taxonomic distinctiveness, levels of genetic variation within and between populations, and the degree of introgression with introduced taxa. The Athabasca River drainage of␣western Alberta, Canada is one of only three (and the largest) drainages flowing east of the continental divide that contain native populations of rainbow trout (Salmonidae: Oncorhynchus mykiss). The “Athabasca” rainbow trout has been considered a preglacial relict worthy of special conservation measures. In addition, the native range of Athabasca rainbow trout has seen many instances of introductions of non-native populations since the beginning of the 20th century. We assayed rainbow trout from the Athabasca River drainage, from hatchery populations, and from representative populations in adjacent regions (N = 49 localities) for variation at 10 microsatelite loci to assess the level of evolutionary distinctiveness of Athabasca rainbow trout, and to assess the levels of introgression with non-native hatchery fish. We found that native Athabasca rainbow trout did not form a distinctive genetic assemblage and that the greatest amount of allele frequency variation was attributable to contemporary drainage systems (29.3%) rather than by a Athabasca/non-Athabasca distinction (12.6%). We found that 78% of all fish were confidently assigned to a “wild” rather than a “hatchery” genetic grouping and that most of the inferred introgression with hatchery fish was restricted to a few localities (N = 6). Our results suggest that: (i)␣Athabasca River rainbow trout are likely postglacial immigrants from adjacent populations of the Fraser River, and (ii) that there is no evidence of widespread introgression of hatchery alleles into native Athabasca River drainage rainbow trout.     

Seasonal changes in reproductive function of the rainbow trout (Salmo gairdneri)

The sequential changes in serum oestradiol 17β (measured by specific radioimmunoassay), vitellogenin (measured by phosphoprotein phosphorus content) and total calcium (measured by fluorimetry) in male and female rainbow trout under a simulated natural photoperiod cycle were investigated. Resting levels of 130 pg/ml serum oestradiol in both male and female fish were found in April and May. In the female, levels reached a peak of 4800 pg/ml in October, and almost returned to resting levels just prior to spawning in mid-January. No significant change from resting levels was seen in the male fish.
In both male and female fish levels of 25 μg/ml serum phosphoprotein phosphorus and 10–14 mg % total serum calcium were found from April to July. Coincident with the rise in oestradiol 17β, in the females serum levels of phospho-protein phosphorus and total calcium increased to 400 uβg/ml and 58 mg% respectively just prior to spawning. In the males no significant change in either of these values was observed throughout the cycle. These results strongly support the hypothesis that photoperiod is the major factor in the environmental control of reproductive activity in the rainbow trout.     

The influence of photoperiod on sexual development in underyearling rainbow trout, Salmo gairdneri Richardson

Photoperiods of 19 h light or more induced sexual maturation in male underyearling rainbow trout but did not influence maturation in the females. Early maturation was not a consequence of the increased growth under long photoperiods. The rate of mortality was much higher in the early maturing males than in the immature fish.     

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.     

Photoperiodic history and a changing melatonin pattern can determine the neuroendocrine response of the ewe to daylength

The reproductive neuroendocrine response of Suffolk ewes to the direction of daylength change was determined in animals which were ovariectomized and treated with constant release capsules of oestradiol. Two groups of animals were initially exposed to 16 or 10 h light/day for 74 days. On day zero of the study, when one group of ewes was reproductively stimulated (elevated LH concentrations) and the other reproductively inhibited (undetectable LH concentrations), half the animals from each group were transferred to an intermediate daylength of 13 h light/day. The remaining ewes were maintained on their respective solstice photoperiods to control for photorefractoriness. LH concentrations rose in animals experiencing a 3 h decrease in daylength from 16L:8D to 13L:11D while LH concentrations fell to undetectable values in those that experienced a 3 h increase in daylength from 10L:14D to 13L:11D. The photoperiodic response of the Suffolk ewe, therefore, depends on her daylength history. Such a result could be explained if the 24-h secretory pattern of melatonin secretion, known to transduce photoperiodic information to the reproductive axis, was influenced by the direction of change of daylength. Hourly samples for melatonin were collected for 24 h 17 days before and three times after transfer to 13L:11D. The melatonin secretory profile always conformed to daylength. Therefore, the mechanism by which the same photoperiod can produce opposite neuroendocrine responses must lie downstream from the pineal gland in the processing of the melatonin signal.     

光周期影响雌性虹鳟鱼的免疫活动

运用放射免疫测定法,酶联免疫吸附法及酶联免疫斑点法调查了性未成熟雌性虹鳟鱼在生殖季节血浆中的皮质醇,雌二醇,睾丸酮,免疫球蛋白Ｍ（ＩｇＭ）,抗体产生细胞等水平的变化,同时也测定了不同光周期条件下ＩｇＭ水平的变化。实验结果表明,伴随生殖季节,血浆中甾醇类激素,ＩｇＭ量和抗体科生细胞数有季节性的变化;另外,生活在不同光周期条件下的虹鳟鱼,血浆中ＩｇＭ的量明显地不同,由于实验是在常温条件下进行的,而且即     

Photoperiod influences the annual reproductive cycle of the male pallid bat (Antrozous pallidus)

Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm.     

Maternal and direct effects of natural-like changes of photoperiod and food condition manipulation on life history parameters in <Emphasis Type="Italic">Daphnia</Emphasis>

This study analyzed changes of life history parameters of a Daphnia pulicaria clone in response to increasing (spring conditions) versus decreasing (fall conditions) photoperiod and low and high food concentrations in maternal and offspring environments. One treatment increased the photoperiod from 12 to 16 h at a rate of 3 min per day, while the other treatment decreased the photoperiod from 16 to 12 h at the same rate. We also used two food concentrations: low (0.2 mg C/l) and high (0.5 mg C/l). Maturation time, first clutch size, survivorship, and somatic growth in offspring depended on the direction of photoperiodic changes for Daphnia grown under high food concentration. Natural-like changes of photoperiod on life history parameters and abrupt changes resulted in similar effects on life history parameters of Daphnia (see Alekseev and Lampert 2004 Hydrobilogia 526:225–230).     

Thermoregulatory responses to variations of photoperiod and ambient temperature in the male lesser mouse lemur: a primitive or an advanced adaptive character?

The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in ambient temperature, evaporative water loss (EWL), body temperature (T _b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions. In both photoperiods, EWL, T _b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated with a decrease in T _b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T _b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed according to daylength. Daily variations in T _b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T _b decrease with or without the occurrence of torpor (T _b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations. Accepted: 4 August 1998     

Increased daylength stimulates plasma growth hormone and gill Na+, K+-ATPase in Atlantic salmon (Salmo salar)

Atlantic salmon juveniles reared at constant temperature (9–10°C) were exposed to four photoperiod treatment and sampled every 2 weeks from January through May. Fish reared under normal photoperiod exhibited eight-and three fold increases in plasma growth hormone and gill Na⁺, K⁺-ATPase activity, respectively, between January and April. Fish exposed to abrupt increases in daylength (LD 15:9) in February or March responded with earlier increases in plasma growth hormone and gill Na⁺, K⁺-ATPase activity, and earlier decreases in condition factor relative to fish in the normal photoperiod group. Fish maintained under short daylength (LD 9:15) from January to May exhibited delayed and muted increases in plasma growth hormone and gill Na⁺, K⁺-ATPase activity. Plasma thyroxine exhibited a 2.5-fold increase from February to late March in the normal photoperiod group, was generally lower in the LD 9:15 group, but exhibited no obvious response to abrupt increases in daylength. There was an increase in plasma 3,5,3-triiodo-l-thyronine with time in all groups (43–80%) but no significant response to photoperiod. Plasma levels of somatostatin-25 were highest in the LD 9:15 group, but there was no detectable response to increased daylength in any of the photoperiod treatments. The results indicate that plasma growth hormone is responsive to increased daylength and may be causally related to subsequent increases in gill Na⁺, K⁺-ATPase.Abbreviations ANOVA two-way analysis of variance - BCA bicinchoninic acid - BSA Bovine serum albumin - EDTA ethylene diamine tetraacetic acid - ELISA enzyme-linked immunosorbent assay - EST eastern standard time - GH growth hormone - GLU Glucagen - IgG Immunoglobulin G - INS Insulin - LDN Simulated natural photoperiod - RIA radio immuno assay - RIA radio immuno assay - SEI Sucrose EDTA imidazole - SS-25 somatostatin-25 - SW sea water - T ₃ 3,5,3 triiodo-l-thyronine - T ₄ thyroxine     

Importance of changing photoperiod and melatonin secretory pattern in determining the length of the breeding season in the Suffolk ewe

Three groups of ovariectomized Suffolk ewes bearing s.c. Silastic implants of oestradiol were subjected to a 90-day priming treatment of an inhibitory long photoperiod (16 h light/day; 16L:8D). On Day 0 of the experiment, they were moved to stimulatory photoperiods. One control group was transferred to 12L:12D and a second control group was transferred to 8L:16D; both groups remained in those photoperiods to determine the timing of reproductive induction and refractoriness. The experimental group was transferred to 12L:12D on Day 0 and then to 8L:16D on Day 55 to determine whether the further reduction in daylength could delay the development of refractoriness. Reproductive neuroendocrine condition was monitored by serum concentrations of LH and FSH. Both gonadotrophins remained elevated for a longer period of time in the experimental group receiving the second reduction in daylength than in either control group, indicating that the second photoperiodic drop delayed the onset of photorefractoriness. Measurement of 24-h patterns of circulating melatonin suggests that the prolonged stimulation of reproductive neuroendocrine activity in the experimental group resulted from a lengthening of the nocturnal melatonin rise. These findings indicate that refractoriness to an inductive photoperiod can be temporarily overcome by exposure to a shorter daylength, and that the change in duration of the nocturnal increase in melatonin secretion is important in photoperiodic signalling. Thus, in natural conditions, the decreasing autumnal daylength, and the resulting expansion of the nocturnal elevation in melatonin secretion, may be utilized to produce a breeding season of normal duration.     

Photoperiodic control of the termination of breeding and the induction ofmoult in House Sparrows Passer domesticus

Two photoperiodic mechanisms controlling gonadal regression in birds have been identified: absolute photorefractoriness, typical of species with short breeding seasons, where gonadal regression occurs spontaneously during long days, and relative photorefractoriness, where a decrease in daylength is required to induce regression. An experiment was designed to test whether these simply represent extremes of one underlying mechanism. Three groups of male House Sparrows Passer domesticus were transferred from a short photoperiod, 8 h of light: 16 h of darkness per day (8L:16D) to long photoperiods of either 18L:6D, 16L:8D or 13L:11D. Gonadal maturation rates were similar in all three groups; gonadal regression and moult began latest in the 13L:11D group. Four additional groups of sparrows were transferred from 8L:16D to 18L:6D and then transferred to either 13L: 11D or 16L:8D prior to, or shortly after, the onset of gonadal regression. The decrease in daylength prior to regression had no effect on the timing of regression but did advance the onset of moult. Decrease in daylength after the onset of regression increased the rate of regression and the rate of moult. Because a decrease in daylength did not affect the timing of regression, the data do not support the hypothesis that absolute and relative photorefractoriness represent extremes of a single underlying photoperiodic control mechanism. The adaptive significance of the effects of decreasing daylength on the rate of regression and moult is discussed.     

Plasma Nesfatin-1 Is Not Affected by Long-Term Food Restriction and Does Not Predict Rematuration among Iteroparous Female Rainbow Trout (Oncorhynchus mykiss)

The metabolic peptide hormone nesfatin-1 has been linked to the reproductive axis in fishes. The purpose of this study was to determine how energy availability after spawning affects plasma levels of nesfatin-1, the metabolic peptide hormone ghrelin, and sex steroid hormones in rematuring female rainbow trout (Oncorhynchus mykiss). To limit reproductive maturation, a group of female trout was food-restricted after spawning and compared with a control group that was fed a standard broodstock ration. The experiment was conducted twice, once using two-year-old trout (second-time spawners) and once using three-year-old trout (third-time spawners). During monthly sampling, blood was collected from all fish, and a subset of fish from each treatment was sacrificed for pituitaries. Pituitary follicle-stimulating hormone-beta (fsh-β) mRNA expression was analyzed with q-RT-PCR; plasma hormone levels were quantified by radioimmunoassay (17β-estradiol and ghrelin) and enzyme-linked immunosorbent assay (11-keto-testosterone and nesfatin-1). Although plasma nesfatin-1 levels increased significantly in the months immediately after spawning within both feeding treatments, plasma nesfatin-1 did not differ significantly between the two treatments at any point. Similarly, plasma ghrelin levels did not differ significantly between the two treatments at any point. Food restriction arrested ovarian development by 15–20 weeks after spawning, shown by significantly lower plasma E2 levels among restricted-ration fish. Pituitary fsh-β mRNA levels were higher among control-ration fish than restricted-ration fish starting at 20 weeks, but did not differ significantly between treatment groups until 30 weeks after spawning. Within both treatment groups, plasma 11-KT was elevated immediately after spawning and rapidly decreased to and persisted at low levels; starting between 20 and 25 weeks after spawning, plasma 11-KT was higher among control-ration fish than restricted-ration fish. The results from these experiments do not provide support for plasma nesfatin-1 as a signal for the initiation of reproductive development in rematuring female rainbow trout.