Purification and development of ELISAs for two forms of vitellogenin in Indian walking catfish, <Emphasis Type="Italic">Clarias batrachus</Emphasis> (L.)

Two forms of vitellogenin (Vg: Vg1 and Vg2) were purified from the plasma of estradiol-17β (E₂)-treated Indian walking catfish, Clarias batrachus, by gel filtration and adsorption chromatography. Native Vg1 and Vg2 had apparent molecular masses of 375 and 450 kDa, respectively, and both Vgs resolved into two similar major bands (95 and 67 kDa) in SDS-PAGE under reducing condition. Polyclonal antisera raised against each form of Vg were absorbed with a combination of hypophysectomized male catfish serum proteins and alternate Vg to ensure specificity. Immunological analyses verified the presence of Vg1 and Vg2 in the plasma of female catfish. Homologous ELISAs were developed for Vg1 and Vg2 using their respective harvested antisera, which exhibited the detection limit of 100 ng ml^?1 for Vg1 and 40 ng ml^?1 for Vg2, and low level of cross-reactivity (not parallel to the standard) was found with alternate Vg in each assay. Treatment of male catfish with E₂ induced both Vgs showing a proportionate ratio of Vg1 to Vg2 at 5.6:1. Plasma concentrations of both Vgs measured by ELISAs at different reproductive phases of field collected female catfish increased in accordance with the ovarian development, keeping the proportionate ratio of Vg1 to Vg2 at about 2:1 in fish undergoing vitellogenesis during prespawning period and 1:20 during spawning period, suggesting that Vg1 may be the major Vg to contribute in yolk formation, whereas Vg2, besides its role in yolk formation, may facilitate other physiological functions. The present study, thus, demonstrates the occurrence of two unequally synthesized Vgs in the catfish.     

The purification and development of a quantitative enzyme linked immunosorbent assay (ELISA) for the measurement of vitellogenin in diploid and triploid brook trout (Salvelinus fontinalis)

Vitellogenin (VTG) was purified from the plasma of estradiol-17β (E₂) treated male brook trout (Salvelinus fontinalis; bt) using gel filtration and anion exchange chromatography. An antiserum to bt-VTG was raised in rabbits, then used to detect bt-VTG by Western blot analysis. Purified bt-VTG and its antibody were then used to develop an antibody-capture, competitive enzyme-linked immunosorbant assay (ELISA). Confirmation of the purified protein as bt-VTG was based on the characteristics of high molecular weight (∼562 kDa), dominant plasma protein in vitellogenic females and induction by exogenous E₂ treatment in males. The antiserum recognized a major 184 kDa polypeptide as well as minor bt-VTG degradation products (150–66 kDa) in purified bt-VTG and in plasma from vitellogenic females. Low levels of antibody cross reactivity were shown with plasma from nonvitellogenic females, control rabbit serum, and several other antisera known to not contain VTG. The ELISA had a minimum detection limit of 8 ng ml⁻¹ and intra- and inter-coefficients of variation less than 9% and 15%, respectively. The ELISA demonstrated parallel binding slopes among dilution curves of purified bt-VTG standard and plasma from diploid and triploid brook trout females. Using the ELISA, maximum plasma VTG levels of 93.5±33.6 mg ml⁻¹ were detected in vitellogenic diploid females, whereas only 0.18±0.15 mg ml⁻¹ were detected in triploid females of the same age (n=5 for each). Diploid and triploid males cohabitating with vitellogenic females showed measurable levels of plasma VTG during vitellogenesis in females (i.e., 0.17 and 0.06 mg ml⁻¹, respectively (n=1)). This revised version was published online in August 2006 with corrections to the Cover Date.     

Photoperiodic manipulations of the reproductive cycle of sea bass (Dicentrarchus labrax) and their effects on gonadal development, and plasma 17ß-estradiol and vitellogenin levels

The annual profile of plasma vitellogenin (VTG) and 17ß-estradiol (E₂) levels, as well as gonadal development and spawning characteristics were investigated in captive female sea bass (Dicentrarchus labrax). Endocrine and gonadal changes were studied in fish reared under natural conditions or exposed to manipulated photothermal cycles. In natural conditions of photoperiod and temperature, sea bass spawned from February through March (East coast of Spain, 40°N 0°E). One or two months of constant long-days (15L/9D) in a constant short-day photoperiod regime (9L/15D) all-year-round, given early in the year (March and March–April), advanced spawning by 3 months. The same treatment applied later in the year (September–October) delayed spawning by 1 month, compared to controls.In all groups, changes in plasma VTG levels were correlated with E₂ levels, oocyte growth and spawning time. In control females, VTG was low (<100 ng ml^-1) during the summer, until its first surge in plasma 4 months before the beginning of spawning. The VTG (3.1 ± 0.3 mg ml^-1) and E₂ (4.1 ± 0.5 ng ml^-1) levels showed a single annual peak during late vitellogenesis, the time of the highest proportion of vitellogenic oocytes in the ovary. Constant high levels of VTG (1–1.4 mg ml^-1) and E₂ (1.6–1.9ng ml^-1) were maintained during the entire spawning time, together with the presence of vitellogenic oocytes, suggesting the existence of several waves of oocyte growth in the ovary and thus, several spawns per female. Endocrine profiles and oocyte development in fish exposed to constant photoperiods were similar to controls, but were shifted in time in relation to the displacement of the spawning time. In the fish showing advanced spawns, the duration of the gametogenic proces was compressed when compared to controls. The differences observed in the evolution of the reproductive-related factors in the advanced groups, which were exposed to a reduction in temperature to 15°C, suggest an influence of the temperature in the early stages of the reproductive cycle in sea bass.     

Using estradiol and progesterone concentrations to assess individual variability in the reproductive cyclicity of captive female little skates, Leucoraja erinacea, from the western Gulf of Maine

In the current study, plasma steroid hormones were used to assess the individual variability of Leucoraja erinacea over the course of 12 months, in hopes of further defining its reproductive cycle. No statistical differences in hormone concentrations were observed between the isolated and non-isolated female skates. Monthly E₂ concentrations ranged from 1,430 pg ml^?1 in August to 3,940 pg ml^?1 in March, indicating the presence of mature ovarian follicles and supporting the conclusions from previous studies that L. erinacea is capable of reproducing year-round. Concentrations of E₂ were significantly elevated or depressed during some months (February, March, June, July, August, and September) of the year, suggesting that reproductive activity may vary over the annual cycle. Even though monthly P₄ concentrations were highly variable, ranging from 82 pg ml^?1 in November to 816 pg ml^?1 in September, no significant reproductive peaks were observed. In addition, a persistently large variation in E₂ and P₄ concentrations, indicative of reproductive asynchrony within (mean CV 62 % and CV 69 %, respectively) and between (mean range CV 78 and 125 %, respectively) individual skates, was observed throughout the study. Collectively, the continually high E₂ concentrations and variability in both hormones observed in the current study are indicative of an oviparous species that reproduces actively throughout the year. However, the weekly sampling frequency revealed that plasma E₂ concentrations, not P₄, were more useful to assess reproductive status in asynchronous continuously breeding oviparous elasmobranchs.     

Disruption of gonadal maturation in cultured Senegalese sole Solea senegalensis Kaup by continuous light and/or constant temperature regimes

A major problem in the development of Senegalese sole Solea senegalensis intensive culture is the poor control on reproduction, in part due to the lack of knowledge on the precise role of photoperiod and temperature. Thus, gonadal maturation was evaluated by assessing the sequential changes in plasma levels of 17β-estradiol (E₂), 11-ketotestosterone (11-KT), and testosterone (T) in both female and male cultured Senegalese sole (F1 generation) exposed to various combinations of constant or naturally-fluctuating daylength and water temperature. Under natural photoperiod (NP; 36° N), exposure to constant temperature (t0; 18-20 °C) disrupted gonadal development, as indicated by a lower incidence (in comparison with naturally-fluctuating water temperature; 14-24 °C) of females at advanced maturation (from February to April: 12 vs. 33%) and running males (from February to May: 46% vs. 57%), and the reduced mean (± S.E.M.) sex steroid plasma levels (female peak E₂ levels: 2.9 ± 0.28 vs. 1.8 ± 0.3 ng ml^− 1; male peak T levels: 1.5 ± 0.14 vs. 0.9 ± 0.06 ng ml^− 1). Therefore, the onset and progression of gonadal development in this species seem to be strongly (“proximally”) influenced by fluctuating water temperature. When compared to NP and t0, exposure to continuous light (LL) under t0 significantly reduced steroid production (female peak E₂ levels: 1.8 ± 0.28 vs. 0.5 ± 0.05 ng ml^− 1; male peak 11-KT levels: 9.4 ± 1.06 vs. 5.4 ± 1.33 ng ml^− 1) and subsequently gonadal development (lower proportions of females at intermediate [46 vs. 6%] and advanced maturation [12 vs. 0%] from February to April and of RM [46 vs. 33%] from February to May). Thus, the seasonal changes of daylength would be crucial for normal gonadal development, being its cueing effects of higher magnitude than those of water temperature. The present report constitutes the first systematic study focused on the environmental control of reproductive events in Senegalese sole.     

The dynamics of in vitro 17 β-estradiol secretion by isolated ovarian follicles of the rainbow trout (Oncorhynchus mykiss)

This study investigated the effects of human chorionic gonadotropin (hCG), 17-hydroxyprogesterone (17P) and testosterone (T) on the in vitro production of 17-estradiol (E₂) by isolated ovarian follicles of the rainbow trout (Oncorhynchus mykiss). 17P at 100 ng ml^-1, and hCG at 100 IU ml^-1 stimulated E₂ production relative to controls, whereas lower doses were ineffective. T was the most effective in stimulating E₂ production, followed by 17P and hCG respectively. The timecourse of E₂ production was investigated for both static culture, and incubations with media replacement, with follicles being exposed to hormone treatment for 30 min, 1 or 3 h, or constantly. E₂ production was observed after 30 min, 3 and 3-6 h in response to T, 17P and hCG respectively. Under static culture, E₂ levels reached maximal levels in 6 h. Longer incubations resulted in further metabolism of E₂ to E₂-glucuronide, which resulted in the blurring of treatment effects after 18 h. Incubations with media replacement resulted in higher E₂ production than in static culture. The results indicate that a 6 h incubation period is sufficient to produce significant increases in E₂ production in response to hCG, 17P and T, and that incubations longer than 12 h result in losses E₂ from the incubation media. These findings have implications for the validity of using static cultures to examine the effects of hormone treatment on the activity of steroid converting enzymes in vitro.     

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E₂), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E₂ levels in females increased rapidly from low values in October (< 0.1 ng ml⁻¹) to peak levels of 3.7 ng ml⁻¹ in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E₂ levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml⁻¹ in November, and peaking again at 3.3 ng ml⁻¹ just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml⁻¹, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml⁻¹ by November, remained elevated throughout the winter, and peaked at 2.8 ng ml⁻¹ I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml⁻¹, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml⁻¹. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.     

Endocrine changes during the annual reproductive cycle of the red porgy, Pagrus pagrus (Teleostei, Sparidae)

Changes in 17-estradiol (E2), estrone (E1), testosterone (T), 11-ketotestosterone (11KT), and 17,20-dihydroxy-4-pregnen-3-one (17,20-P) levels were correlated to changes in gonadosomatic index (GSI), vitellogenin concentration (Vg), ovarian and testicular histology during the annual reproductive cycle of the red porgy, Pagrus pagrus. The production of E2, E1, T and 17,20-P was confirmed by analysis of the steroidogenic activity of ovaries. In females, the average concentration of E2 was lower than 2 ng ml^–1. E2 values first increased significantly at the stage of endogenous vitellogenesis and remained high during exogenous vitellogenesis. E1 levels were lower values than E2 (less than 300 pg ml^–1), but they increased at the beginning of exogenous vitellogenesis. Estrogens concentrations followed similar pattern to Vg and were significantly correlated. Mean levels of T were mostly lower than 1 ng ml^–1. They followed a pattern similar to that of E2 except for a further increase observed at the stage of final maturation. T and E2 levels were significantly correlated. The concentration of 11KT did not change significantly. The levels of 17,20-P ranged between 0.22 and 1.22 ng ml^–1 but changes were not related to gametogenesis. In males, the concentrations of T and 11KT fluctuated significantly during the sexual maturity stages, showing a similar pattern and were significantly correlated to GSI changes. T levels increased during spermiogenesis and spermiation stages to reach about 3 ng ml^–1. 11KT levels stayed about half those of T. The levels of estrogens showed no significant changes. Level of 17,20-P showed no significant variation related to male maturity. Results are discussed in relation to changes in plasma steroid levels during gametogenesis of other multiple spawner species.     

Plasma steroid levels and follicular development in the female staghorn damselfish Amblyglyphidodon curacao

Female staghorn damselfish were captured from coral reefs by divers and bloodsampled. Ovarian follicle type and size distribution were correlated with plasma levels of the ovarian steroids testosterone (T) and 17β-estradiol (E₂). Ovaries contained up to three clutches of vitellogenic follicles and steroid levels were maximal when all three clutches were present.     

Changes in gonadal hormones during oocyte development in the striped bass,Morone saxatilis

Wild striped bass,Morone saxatilis, were collected from coastal waters and spawning areas to describe the endocrine correlates of oocyte development in non-captive, migratory fish. The fish were classified according to their most advanced oocytes. Serum levels of estradiol (E₂), testosterone (T) and 17-20-dihydroxyprogesterone (DHP) were measured by radioimmunoassay (RIA). Females in the primary growth phase and early secondary growth phase (pre-vitellogenic) had low levels of plasma steroids, ovarian lipid content and gonadosomatic indices (GSIs). Significant increases in E₂, T, ovarian lipid content and GSIs occurred during the vitellogenic phase. Maximum levels of all reproductive parameters were found in prespawning fish sampled in the Hudson River. Mean levels of E₂, T, ovarian lipids and GSIs for these fish were 2.0±0.5 ng/ml, 3.0±0.3 ng/ml, 24±1 mg/g, and 5.6±0.3% (mean±SEM), respectively. In fish induced to spawn with human chorionic gonadotropin (HCG), DHP levels (1.9±0.4 ng/ml) were significantly elevated. Similar levels were found in two fish captured during the spawning season, suggesting that DHP may serve as the maturation-inducing steroid in this species.     

Involvement of androgens and growth hormone in the synthesis of vitellogenin in Japanese eel (Anguilla japonica)

Immature eels positively responded to estradiol-17β (E₂) injection in terms of vitellogenin (Vg) synthesis but not to growth hormone (GH) or 17α-methyltestosterone (MT) injection. However, injection of MT or GH combined with E₂ strongly increased Vg synthesis. In in vitro experiments, eel hepatocytes treated with E₂, GH, or MT alone did not produce detectable amount of Vg, whereas the combination of E₂ with GH or MT, or both greatly increased Vg synthesis in the hepatocytes.     

The modulating effect of vitellogenin on the synthesis of 17β-estradiol by rainbow trout (Oncorhynchus mykiss) ovary

In vivo induction of vitellogenin (VTG) in response to the administration of 17-estradiol (E₂) was achieved and the protein was isolated by gel filtration column chromatography of plasma samples. Adult female trout were injected with the vitellogenic fraction every ten days from July to November and levels were measured by RIA from September to December. The results showed a significant decrease (p<0.01) in plasma E₂ levels in injected females compared with the controls. In December, after finishing the treatment, the plasma E₂ concentration increased, in injected females to reach a level similar to that of control females at vitellogenesis. The in vitro study showed that in early vitellogenic oocyte (from September) the presence of the vitellogenic fraction in the incubation medium causes a significant decrease (p<0.01) in the synthesis of E₂ by the oocytes. These data suggest that the concentration of the VTG into the oocyte can alter VTG production by the liver, moderating the production of E₂ by the ovary.     

Effect of in vitro xenoestrogens on steroidogenesis in mature female fish, Chasmichthys dolichognathus

In this study, fully vitellogenic oocytes of the longchin goby (Chasmichthys dolichognathus) were exposed to in vitro xenoestrogens such as diethylstilbestrol (DES), bisphenol A (BPA) and nonylphenol (NP) at concentrations of 100 ng/ml in the presence of [³H]17α-hydroxyprogesterone as precursor. The major metabolites produced in vitro are progestogens [17α-hydroxy,20α-dihydroprogesterone (17α20αOHP) and 17α-hydroxy,20β-dihydroprogesterone (17α20βOHP)], androgens [androstenedione (A4) and testosterone (T)] and estrogens [estrone (E1) and estradiol-17β (E2)]. Comparative activities of these chemicals in oocyte steroid biosynthesis showed as follows: NP treatment resulted in clear stimulation of estrogen production, while the opposite occurred in DES treated incubation. Treatment with DES resulted in a higher synthesis of 17α20αOHP. BPA treatment increased the androgen, while estrogen synthesis was slightly inhibited. These results suggest that NP exhibited clearly estrogenic activity on the three chemicals.     

A unique lipoprotein profile found in the plasma of cultured Japanese eelAnguilla japonica: very low density lipoprotein,but not high density lipoprotein,is the main component of plasma

A unique lipoprotein profile was found in the plasma of cultured Japanese eel,Anguilla japonica which accumulated more lipid in its muscle than in its liver. The plasma lipoprotein level of Japanese eels was in excess of 54 mg ml¹, a concentration considered to be hyperlipoproteinemic in relation to other teleosts. The plasma lipoproteins consisted of very low density lipoprotein (VLDL, density (d)<1.006 g ml¹) low density lipoprotein (LDL, 1.0061), high density lipoprotein 2 (HDL₂, 1.0851), and HDL₃ (1.1001). VLDL, but not HDL, was the main component in the plasma of Japanese eels, unlike most teleosts where HDL is the main component. An additional lipoprotein, vitellogenin (1.2101), was induced by the injection of estradiol-17ß (E₂), but VLDL was the main plasma component even in the E₂-treated eels. VLDL was a triacylglycerol (TG)-rich lipoprotein and possessed two apolipoprotein (apo) B-like proteins of molecular weights (Mr) 260K and 230K as main components.LDL, HDL₂, and HDL₃ were revealed to consist of heterogeneous components by a density gradient ultracentrifugation. LDL was separated into three subclasses of LDL₁ (1.0301), LDL₂ (1.0431), and LDL₃ (1.0671). LDL₁ with apo B-like protein of Mr 230K was a TG-rich lipoprotein, while both LDL₂ and LDL₃ were cholesterol ester-rich lipoproteins with apo A-I-and A-II-like proteins of Mr 25K and 14K. The particle sizes of HDL₂ and HDL₃ subclasses differed, although all of HDL₂ and HDL₃ subclasses possessed apo A-I-and A-II-like proteins of Mr 25K and 14K as main components. To our knowledge, this is the first report of detailed plasma lipoprotein profile in Japanese eels.Corresponding author: till August 18, 1996 and after April 19, 1997: at the above address. From August 19, 1996 till April 18. 1997: c/o Dr. N.H. Haunerland, Department of Biological Sciences. Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.     

The development of a radioimmunoassay for carp,Cyprinus carpio,vitellogenin

The development of an easily — performed and robust radioimmunoassay (RIA) to carp, Cyprinus carpio, vitellogenin (c-VTG) is described. Purified c-VTG was iodinated using Iodogen. The resulting c-VTG label was useful for up to 60 days. High titre antibodies were raised in rabbits to the purified c-VTG. The practical operating range of the c-VTG RIA was between 2 and 200 ng. ml^-1. VTG was detected in plasma from all female mirror carp investigated, and all plasmas diluted parallel to the standard. The plasma VTG level in female carp increased concomitantly with the GSI; levels increasing from the ng. ml^-1 level in juveniles to a maximum of 1 mg. ml^-1 in fully mature females. VTG level was a far more sensitive index of the degree of sexual development than was GSI. In males, blood levels of VTG were always undetectable. Vitellogenic plasma from all subspecies of C. carpio (e.g. mirror, common, Koi) diluted parallel to the standard, as did blood from most other female cyprinids, such as the roach (Rutilis rutilis), bream (Abramis brama), and dace (Leuciscus leuciscus), but not all. These results suggest that the structure of VTG is highly conserved within this family. However, plasma from vitellogenic salmonids did not cross-react in the RIA. The relationship between plasma VTG and calcium levels was studied in both carp and rainbow trout. In rainbow trout it was found that plasma calcium levels do not rise above basal levels until the VTG level exceeds about 1 mg. ml^-1, and therefore in this species it is only useful as an indicator of the degree of ovarian development in the later stages of the reproductive cycle. In the carp, however, and probably other cyprinids, blood VTG levels do not appear to naturally exceed about 1 mg.ml^-1, and plasma calcium levels are not suitable as an indirect measure of the VTG level.     

Stress responses and disease resistance in salmonid fish: Effects of chronic elevation of plasma cortisol

Basal levels of plasma cortisol in unstressed salmonid fish are normally in the range 0–5 ng ml⁻¹. An acute stress such as handling or 1 h confinement caused a temporary elevation of the plasma cortisol levels of both brown trout,Salmo trutta L., and rainbow trout,Salmo gairdneri Richardson, in the range 40–200 ng ml⁻¹ with a return to basal levels within 24–48 h. The extent of the cortisol elevation in response to an acute stress was dependent upon both the species and strain of trout. Chronic stresses, such as prolonged confinement or crowding, resulted in an elevation of plasma cortisol levels to approximately 10 ng ml⁻¹. Under these circumstances, blood cortisol levels remained elevated for periods of up to 4 weeks before acclimation finally occurred. It is shown, by means of intraperitoneal implantation of cortisol, that chronic elevation of plasma cortisol levels in the brown trout results in a dose-dependent increase in mortality due to common bacterial and fungal diseases. This effect is apparent at plasma cortisol levels as low as 10 ng ml⁻¹, levels below those often reported as being representative of ‘unstressed’ fish. These findings are discussed in relation to the known immunosuppressive effects of corticosteroids in teleost fish.     

Seasonal changes in reproductive condition and plasma levels of sex steroids in the blue cod,Parapercis colias (Bloch and Schneider) (Mugiloididae)

Gonad and plasma samples were taken from blue cod captured throughout the reproductive cycle, gonad condition was assessed, and plasma levels of 17-hydroxyprogesterone (17OHP), 17,20-dihydroxy-4-pregnen-3-one (17,20P), testosterone (T), 17-estradiol (E₂) and estrone (E₁) were measured by radioimmunoassay. It was confirmed that spawning occurred over an extended period in late winter and spring, with individual fish being involved in multiple spawning events. Plasma levels of T were bimodal in both sexes with peaks (maximum of 6.0 ng.ml^–1) occurring 2 months prior to, and also during the early part of the spawning period. 17,20P was elevated in males (2.1 ng.ml^–1) in mid-spermatogenesis coinciding with the first T peak (4.9 ng.m.^–1). 17,20P was detectable but not significantly elevated (0.6–1.2 ng.ml^–1) at any sample time in females. E₂ was elevated in mature females (1.0 ng.ml^–1) early in the spawning period but remained at assay detection limits (0.3 ng.ml^–1) at all other sample times. Neither 17OHP nor E₁ were detectable in the plasma of either sex. It is suggested that bimodal increases in sex steroids prior to spawning may be a feature of species with rapid recrudescence.     

The Effect of Photoperiod on Sexual Maturation,Appetite and Growth in Wild Atlantic Cod (Gadus morhua L.)

An experiment was conducted to examine (a) the effects of photoperiod on timing of sexual maturation (b) the relationship between plasma steroid levels, appetite and growth in male and female Atlantic cod (Gadus morhua L.). Wild caught Norwegian coastal cod were subjected to either a 6L/18D photoperiod typical of January at 60° N-(Short day group) or a simulated natural photoperiod (Normal day group) from June 2000 until spawning started. Appetite of individual fish were measured twice weekly, while weight, length and plasma levels of the sex steroids testosterone (T), 11 keto-testosterone (11-KT) and estradiol-17β (E2) were monitored bimonthly. Cod in the Short day group matured 3 months ahead of the cod in the Normal day group and started spawning in early November. Appetite decreased in both sexes 2–3 months prior to spawning in both groups, but this reduction was stronger among males. In both sexes, length growth was reduced concurrently with the appetite loss. Overall, females had significantly higher somatic growth, put relatively less energy into length growth and had developed larger livers compared to males at the time of spawning in the Short day group. Plasma steroid levels increased in both groups throughout the experiment, reaching peak levels of ca 10 ng ml⁻¹ (T) and 15–20 ng ml⁻¹ (11-KT) in males, and 1.5–2 ng ml⁻¹ (T) and 12–18 ng ml⁻¹ (E2) in females at the onset of spawning. Steroid levels increased more rapidly among Short day cod verifying the earlier onset of maturation. These results confirm that photoperiod is a major cue to maturation in cod and imply that the high cost of spawning for females incur differences in appetite between the sexes.     

Effect of triiodothyronine on the growth and survival of larval striped bass (Morone saxatilis)

This study was carried out to test the effect of triiodothyronine (T₃) on the growth and survival of larval striped bass (Morone saxatilis). Growth and survival of striped bass held in 5 ppt seawater and treated with various doses of T₃ were measured beginning at 5 and 16 days after hatching. Body content of T₃ was measured by radioimmunoassay. T₃ dissolved in the 5 ppt seawater was taken up by larval striped bass in a dose-dependent manner, and affected the growth and survival of the fish. At 5 days after hatching, T₃ at 100 ng ml^–1 and 50 ng ml^–1 retarded the growth of larval striped bass and caused a lower survival rate than T₃ at 25 ng ml^–1 or the control treatment. At 16 days after hatching, T₃ at 100 ng ml^–1 retarded the growth of larval fish and caused a higher mortality. T₃ at 10 ng ml^–1 and 1 ng ml^–1 did not show any effect on either survival or growth. Body content of T₃ returns to control levels within days following end of treatment. The results indicate that exogenous T₃ can be detrimental to the growth and survival of larval striped bass.     

Serum steroid profiles in artificially maturing female Japanese eel,Anguilla japonica

To investigate whether steroid profiles in salmon pituitary homogenate (SPH)-induced artificially maturing Japanese eel, Anguilla japonica, resemble those in other, naturally maturing fishes, the daily changes in 11 steroids were analyzed for a 70-day period (average time needed to reach the maturational phase). Concentrations of most steroids were low and changed on a weekly basis, with maximum values 2–5 days after an SPH injection. Thus, pregnenolone, 17α-hydroxypregnenolone, dehydroepiandrosterone, progesterone, 17α-hydroxyprogesterone, 17α,20 β-dihydroxy-4-pregnen-3-one, androstenedione and estrone levels were barely or not detectable in serum throughout the experimental period, which is largely in keeping with what is known about oogenesis-related steroids in other fishes. In contrast, serum testosterone (T) levels were high, but fluctuated considerably with each SPH injection (about 0.3–8.3 ng/ml). The serum estradiol-17β (E₂) levels increased after SPH injections and gradually rose throughout the experiment, peaking at the end of the experimental period (about 0.2–7.8 ng/ml). Serum levels of 11-ketotestosterone (11-KT) before SPH treatment were higher (approximately 2 ng/ml) than those of the other steroid hormones (less than 0.5 ng/ml). 11-KT levels increased gradually over the experimental period, and, like E₂, levels peaked towards the end of the experimental period (about 15 ng/ml). The observed patterns for T, E₂ and 11-KT are unlike those in other fishes. Furthermore, the consistent elevations in levels of 11-KT, both before and after SPH treatment, are suggestive of an important role for this steroid in controlling oocyte growth.