Intraspecific alkaloid variation in ladybird eggs and its effects on con- and hetero-specific intraguild predators

Sexual size dimorphism (SSD) is a common phenomenon in animals. In many species females are substantially larger than males. Because body size plays a central role in modulating the body temperature (T _b) of ectotherms, intersexual differences in body size may lead to important intersexual differences in thermoregulation. In addition, because SSD is realized by differences in growth rate and because growth rate is strongly temperature dependent in ectotherms, a conflict between male reproductive behaviour and thermoregulation may affect the expression of SSD. In this study, we investigated the thermal implications of SSD in a reptile exhibiting spectacular female-biased SSD: the northern map turtle (Graptemys geographica). Over three seasons, we collected >150,000 measurements of T _b in free-ranging adult and juvenile northern map turtles using surgically implanted miniature temperature loggers. Northern map turtles exhibited seasonal patterns of thermoregulation typical of reptiles in northern latitudes, but we found that large adult females experienced a lower daily maximum T _b and a narrower daily range of T _b than adult males and small juvenile females. In addition, despite more time spent basking, large adult females were not able to thermoregulate as accurately as small turtles. Our findings strongly suggest that body size limits the ability to thermoregulate accurately in large females. By comparing thermoregulatory patterns between adult males and juvenile females of similar body size, we found no evidence that male reproductive behaviours are an impediment to thermoregulation. We also quantified the thermal significance of basking behaviour. We found, contrary to previous findings, that aerial basking allows northern map turtles to raise their T _b substantially above water temperature, indicating that basking behaviour likely plays an important role in thermoregulation.     

Thermal biology and temperature-based habitat selection in a large aquatic ectotherm, the alligator snapping turtle, Macroclemys temminckii

Ectotherms in water experience rates of heat transfer at least two orders of magnitude greater than in air, seriously constraining their thermoregulatory capabilities. Yet, even in water, individuals may exert control over body temperature (T_b) via behaviors such as selecting thermally favorable microhabitats. The interactions among body size, physiology, and behavior on the thermal biology of large, entirely aquatic, ectotherms is poorly understood. We tested the hypothesis that alligator snapping turtles (Macroclemmys temminckii) selected microhabitats based on temperature by comparing temperatures at sites used by turtles to temperatures at randomly selected sites. These large turtles selected a narrow range of microhabitats that were significantly warmer and less variable in temperature than random sites. Cooling trials in the laboratory indicated larger turtles equilibrated more slowly to ambient temperature (T_a) than smaller turtles. We recorded T_a and body temperature (T_b) of turtles in the field continuously throughout the year. The T_b generally conformed to T_a but there were periods when T_b−T_a differences were great. These results suggest that while physiology and size of aquatic turtles can affect T_b transiently, microhabitat selection may be the only meaningful mechanism for large, entirely aquatic, turtles to control T_b.     

Thermoregulation of spotted turtles (Clemmys guttata) in a beaver-flooded bog in southern Ontario,Canada

Body temperature has a major influence on the physiological processes, growth, reproductive output, and overall survival of ectotherms. When a habitat is altered as a result of natural or anthropogenic influences, the available temperatures in the habitat can change, thus affecting an animal's ability to thermoregulate. We studied thermoregulation in response to habitat change in a population of spotted turtles (Clemmys guttata) in Southern Ontario, Canada. Historically, the study site was ditched to draw down water levels to facilitate peat mining, and the resulting drainage ditches were the only habitat containing surface water and turtles were restricted to these drains. Recent colonization of the site by beaver (Castor canadensis) caused increases in water level and water surface area. We followed spotted turtles (N=16) outfitted with radio transmitters and iButtons to estimate body temperatures (T_b) continuously throughout the active season post-flooding. Turtle models outfitted with iButtons (N=50) were deployed in the nine available habitat types to record environmental temperatures (T_e). Turtles (N=13) were tested in a thermal gradient under laboratory conditions to determine preferred body temperature range (T_set). The T_set for the population ranged from 20 °C to 26 °C. In the field, T_b was within the T_set range 28% of the time from March to October, and 67% of the time from July to August. Efficiency of thermoregulation was calculated to be highest in July and August. The habitat type with the highest thermal quality was the shallow flooded zone created by beaver damming, and the habitat with the lowest thermal quality was the drain bottom, the drains being the only aquatic habitat available prior to flooding. This study confirms that beaver flooding provided a wide variety of preferable thermal opportunities for spotted turtles. Further investigation is needed to determine the effects of flooding on spotted turtle thermoregulation during nesting and hibernation.     

Home‐site fidelity and homing behavior of the big‐headed turtle Platysternon megacephalum

Site fidelity refers to the restriction of dispersal distance of an animal and its tendency to return to a stationary site. To our knowledge, the homing ability of freshwater turtles and their fidelity is reportedly very low in Asia. We examined mark–recapture data spanning a 4‐year period in Diaoluoshan National Nature Reserve, Hainan Province, China, to investigate the site fidelity and homing behavior of big‐headed turtles Platysternon megacephalum. A total of 11 big‐headed turtles were captured, and all individuals were used in this mark–recapture study. The site fidelity results showed that the adult big‐headed turtles (n = 4) had a 71.43% recapture rate in the original site after their release at the same site, whereas the juveniles (n = 1) showed lower recapture rates (0%). Moreover, the homing behavior results showed that the adults (n = 5) had an 83.33% homing rate after displacement. Adult big‐headed turtles were able to return to their initial capture sites (home) from 150 to 2,400 m away and precisely to their home sites from either upstream or downstream of their capture sites or even from other streams. However, none of the juveniles (n = 4) returned home, despite only being displaced 25–150 m away. These results indicated that the adult big‐headed turtles showed high fidelity to their home site and strong homing ability. In contrast, the juvenile turtles may show an opposite trend but further research is needed.     

Sex differences in DHEA and estradiol during development in a wild songbird: Jugular versus brachial plasma

Sexual differentiation of the brain has traditionally been thought to be driven by gonadal hormones, particularly testosterone (T). Recent studies in songbirds and other species have indicated that non-gonadal sex steroids may also be important. For example, dehydroepiandrosterone (DHEA) - a sex steroid precursor that can be synthesized in the adrenal glands and/or brain - can be converted into active sex steroids, such as 17β-estradiol (E₂), within the brain. Here, we examine plasma DHEA and E₂ levels in wild developing European starlings (Sturnus vulgaris), from hatch (P0) to fledging (P20). Blood samples were collected from either the brachial vein (n = 143) or the jugular vein (n = 129). In songbirds, jugular plasma is enriched with neurally-synthesized steroids and, therefore, jugular plasma is an indirect measure of the neural steroidal milieu. Interestingly, brachial DHEA levels were higher in males than females at P4. In contrast, jugular DHEA levels were higher in females than males at P0 and P10. Brachial E₂ levels were higher in males than females at P6. Surprisingly, jugular E₂ levels were not high and showed no sex differences. Also, we calculated the difference between brachial and jugular steroid levels. At several ages, jugular steroid levels were lower than brachial levels, particularly in males, suggesting greater neural metabolism of circulating DHEA and E₂ in males than females. At a few ages, jugular steroid levels were higher than brachial levels, suggesting neural secretion of DHEA or E₂ into the general circulation. Taken together, these data suggest that DHEA may play a role in brain sexual differentiation in songbirds.     

A multidisciplinary study on social status and the relationship between inter-individual variation in hormone levels and agonistic behavior in a Neotropical cichlid fish

Social animals with hierarchal dominance systems are particularly susceptible to their social environment. There, interactions with conspecifics and hierarchal position can greatly affect an individual's behavior, physiology and reproductive success. Our experimental model, Cichlasoma dimerus, is a serially-monogamous Neotropical cichlid fish with a hierarchical social system, established and sustained through agonistic interactions. In this work, we aimed to describe C. dimerus social structure and its association with hormonal profiles and testicular cellular composition. We recorded and quantified agonistic interactions from the territorial pair, i.e. the top ranked male and female, and the lowest ranked male of stable social groups. Plasma levels of 11-ketotestosterone (11-KT), testosterone, 17β-estradiol (E₂) and cortisol were measured by ELISA. Results show that territorial pairs cooperatively guarded the territory, but rarely attacked in synchrony. Territorial males had higher testosterone and 11-KT plasma levels than non-territorial males, while E₂ and an index of its metabolization from testosterone were higher in non-territorial males. No difference was observed in cortisol levels. Plasma 11-KT and an index of the conversion of testosterone to 11-KT, positively correlated with the frequency of aggressiveness, while E₂ showed the opposite pattern. Territorial males had a higher gonadosomatic index than non-territorial males. The quantification of testicular cellular types revealed that the percentage of spermatocytes and spermatids was higher in non-territorial males, while territorial males showed a greater percentage of spermatozoa. Thus, C. dimerus male social position within a stable hierarchy is associated with distinct behaviors, steroid levels and testicular degree of development.     

Endocrine Control of Embryonic Diapause in the Australian Sharpnose Shark Rhizoprionodon taylori

The reproductive cycle of the Australian sharpnose shark, Rhizoprionodon taylori, includes a temporary suspension of development at the commencement of embryogenesis termed embryonic diapause. This study investigated levels of 17β-estradiol (E₂), testosterone (T) and progesterone (P₄) in plasma samples of mature wild female R. taylori captured throughout the reproductive cycle and correlated them with internal morphological changes. Levels of T were elevated through most of the embryonic diapause period, suggesting a role of this hormone in the maintenance of this condition. Increasing plasma T concentrations from late diapause to early active development were associated with a possible role of androgens in the termination of embryonic diapause. As in other elasmobranchs, a concomitant increase of E₂ with ovarian follicle size indicated a direct role of this hormone in regulating vitellogenesis, while a peak in P₄ suggested this hormone is associated with preovulation and ovulation. Additionally, significant correlations between photoperiod or water temperature and maximum follicular diameter and hepatosomatic index suggest that these abiotic factors may also play a role triggering and regulating the synchrony and timing of reproductive events.     

Causes of Stranding and Mortality,and Final Disposition of Loggerhead Sea Turtles (Caretta caretta) Admitted to a Wildlife Rehabilitation Center in Gran Canaria Island,Spain (1998-2014): A Long-Term Retrospective Study

Aims

The aims of this study were to analyze the causes of stranding of 1,860 loggerhead turtles (Caretta caretta) admitted at the Tafira Wildlife Rehabilitation Center in Gran Canaria Island, Spain, from 1998 to 2014, and to analyze the outcomes of the rehabilitation process to allow meaningful auditing of its quality.

Methods

Primary causes of morbidity were classified into seven categories: entanglement in fishing gear and/or plastics, ingestion of hooks and monofilament lines, trauma, infectious disease, crude oil, other causes, and unknown/undetermined. Final dispositions were calculated as euthanasia (E_r), unassisted mortality (M_r), and release (R_r) rates. Time to death (T_d) for euthanized and dead turtles, and length of stay for released (T_r) turtles were evaluated.

Results

The most frequent causes of morbidity were entanglement in fishing gear and/or plastics (50.81%), unknown/undetermined (20.37%), and ingestion of hooks (11.88%). The final disposition of the 1,634 loggerhead turtles admitted alive were: E_r = 3.37%, M_r = 10.34%, and R_r = 86.29%. E_r was significantly higher in the trauma category (18.67%) compared to the other causes of admission. The highest M_r was observed for turtles admitted due to trauma (30.67%). The highest R_r was observed in the crude oil (93.87%) and entanglement (92.38%) categories. The median T_r ranged from 12 days (unknown) to 70 days (trauma).

Conclusions

This survey is the first large-scale epidemiological study on causes of stranding and mortality of Eastern Atlantic loggerheads and demonstrates that at least 71.72% of turtles stranded due to anthropogenic causes. The high R_r (86.29%) emphasizes the importance of marine rehabilitation centers for conservation purposes. The stratified analysis by causes of admission of the three final disposition rates, and the parameters T_d and T_r should be included in the outcome research of the rehabilitation process of sea turtles in order to allow comparative studies between marine rehabilitation centers around the world.     

Cloning and characterization of vitellogenin cDNA from the common Japanese conger (Conger myriaster) and vitellogenin gene expression during ovarian development

The major yolk protein precursor, vitellogenin (VTG) was detected in plasma from vitellogenic females and estradiol-17β (E₂)-treated immature females, but not in males and immature females by Western blotting in common Japanese conger Conger myriaster. Its molecular mass was approximately 180 kDa under denaturing and reducing conditions. The common Japanese conger VTG cDNA was cloned from the liver of vitellogenic female. It contains 5110 nucleotides including an open reading frame that encodes 1663 amino acids. The deduced amino acid sequence of the common Japanese conger VTG shares 80% identity with that of eel Anguilla japonica VTG-1, and 45–55%, 32–34% and 27–29% identity with the deduced amino acid sequences of other fish, amphibian and avian VTG with polyserin domain, respectively. In female common Japanese conger, VTG gene was highly expressed in the liver of this species similar with other oviparous vertebrates. The expression levels of VTG gene in the liver increased from the oil droplet stage to the tertiary yolk globule stage and were maintained until the migratory nucleus stage.     

Age structure and growth of Semotilus atromaculatus(Mitchill) in PCB‐contaminated streams

Creek chub Semotilus atromaculatus from two PCB contaminated streams (Clear Creek and Richland Creek) at three locations and a reference stream (Little Indian Creek), Indiana, U.S.A., were examined to determine if age class structure and growth variables were correlated with in‐situ PCB exposure. Approximately five to 15 fish were captured weekly during the spring spawning season and monthly thereafter for a 12 month period. Fish collected ranged from 25 to 267 mm total length (L_T). Throughout the course of this study, no spawning activity was observed at either location in Clear Creek, although some very small young‐of‐the‐year (YOY) creek chub fry were observed at the downstream location by late summer. Creek chub nests were observed in both Richland Creek and Little Indian Creek but YOY were common only in Little Indian Creek. Exposure to PCBs was shown to both enhance and decrease growth in varied laboratory tests; subtle but significant gender‐specific differences in the growth of creek chub populations between the sites were observed. Creek chub up to 24 months in age from Clear Creek and Richland Creek were significantly larger (both L_T and mass for males and L_T for females) than reference site creek chub. This trend was reversed for creek chub aged ≥24 months as the reference site fish were consistently larger with reference males weighing significantly more. Older age classes of creek chub were missing in areas of higher PCB contamination. Female population growth rates and individual instantaneous growth rates were consistently higher at the reference site in comparison to the PCB‐contaminated sites. Calculation of ‘functional b’(as a condition factor) did indicate that growth enhancement in young males did occur at the most contaminated site and reductions in growth (mass relative to L_T) occurred in females from all contaminated sites. Furthermore, long‐term survivorship for females was reduced in the PCB‐contaminated streams. All of these subtle alterations in growth would not have been observed if males and females had not been analysed separately.     

Molecular Characterization of Japanese Sillago Vitellogenin and Changes in Its Expression Levels on Exposure to 17β-Estradiol and 4-<Emphasis Type="Italic">tert</Emphasis>-Octylphenol

We cloned a full-length cDNA encoding vitellogenin (VTG) from a marine teleost, the Japanese sillago Sillago japonica. The cloned sillago VTG contained signal peptide, lipovitellin heavy chain, phosvitin, lipovitellin light chain, and β′-component in the order from the N-terminus. An exposure to 17β-estradiol significantly increased the levels of plasma VTG, but not hepatic VTG mRNA in males. Neither plasma VTG nor hepatic VTG mRNA levels were affected by the exposure to 4-tert-octylphenol. Hepatic VTG mRNA levels in males increased at 1 day after intraperitoneal administration of 17β-estradiol but decreased in the subsequent 5 days. However, plasma VTG levels remained high for 5 days after administration, suggesting that the accumulation period of plasma VTG is longer than that of hepatic VTG mRNA in males. Therefore, VTG mRNA may be a suitable indicator of temporal exposure to estrogenic chemicals in the environment, whereas plasma VTG is useful to detect consecutive exposure.     

Zygoparity and sex steroid hormone profiles in bluemouth Helicolenus dactylopterus

Two hundred and seven individuals (103 females and 104 males) of bluemouth Helicolenus dactylopterus (Scorpaeniformes, Sebastidae), a commercially important deep‐water species with an unusual reproductive strategy, from the eastern Atlantic Ocean ranging from 13·9 to 37·5 cm total length (L_T) were analysed from September 2011 to October 2012. The analysis included gonad maturity phases and blood‐plasma levels of oestradiol‐17β (E₂), 11‐ketotestosterone (11‐KT) and 17,20β‐dihydroxypregn‐4‐en‐3‐one (17,20β‐P). Results confirmed the existence of an annual reproductive cycle with asynchrony between females and males and a spawning season from January to May. A pronounced peak in 17,20β‐P in October for both sexes was associated with possible mating behaviour and recent copula. Levels of E₂ increased preceding the elevation of the gonado‐somatic index during ovarian growth and were lower during regression and regeneration. The frequency distribution of oocyte–embryonic stages and variation of hormone levels suggest the existence of daily rhythms. Fertilization was detected between 2000–0000 and 0800–1200 h and spawning took place throughout the day peaking between 2000 and 0000 h. The cyclic pattern of sex steroids and ovarian recruitment provides a new insight into the reproductive strategy of this species.     

Daily and annual patterns of thermoregulation in painted turtles (Chrysemys picta marginata) living in a thermally variable marsh in Northern Michigan

The capacity for an ectothermic reptile to thermoregulate has implications for many components of its life history. Over two years, we studied thermoregulation in a population of Midland painted turtles (Chrysemys picta marginata) in a shallow, thermally variable wetland during summer in Northern Michigan. Mean body temperature (T_b) of free-ranging turtles was greater in 2008 (25.8 °C) than in 2010 (19.7 °C). Laboratory determined thermoregulatory set point (T_set) ranged from 25 °C (T_set-min) to 31 °C (T_set-max) and was lower during the fall (17–26 °C). Deviations of T_b distributions from field measured operative temperatures (T_e) and indices of thermoregulation indicated that C. picta marginata were capable of a limited degree of thermoregulation. Operative temperatures and thermal quality (d_e=|T_set-min−T_e| and |T_e−T_set-max|) cycled daily with maximal thermal quality occurring during late morning and late afternoon. The accuracy of thermoregulation (d_b=|T_set-min−T_b| and |T_b−T_set-max|) was maximal (d_b values were minimal) as T_b declined and traversed T_set during the late afternoon–early evening hours and was higher on cloudy days than on sunny days because relatively low T_e values decreased the number of T_b values that were above T_set. Our index of thermal exploitation (E_x=frequency of T_b observations within T_set) was 36%, slightly lower than that reported for an Ontario population of C. picta marginata. Regression of d_b (thermal accuracy) on d_e (thermal quality) indicated that turtles invested more in thermoregulation when thermal quality was low and when water levels were high than when they were low. There were no intersexual differences in mean T_b throughout the year but females had relatively high laboratory determined T_b values in the fall, perhaps reflecting the importance of maintaining ovarian development prior to winter.     

Steroid hormones and aggression in female Galápagos marine iguanas

We studied steroid hormone patterns and aggression during breeding in female Galápagos marine iguanas (Amblyrhynchus cristatus). Females display vigorously towards courting males after copulating (female-male aggression), as well as fight for and defend nest sites against other females (female-female aggression). To understand the neuroendocrine basis of this aggressive behavior, we examined changes in testosterone (T), estradiol (E₂), corticosterone (CORT), and progesterone (P₄) during the mating and nesting periods, and then measured levels in nesting females captured during aggressive interactions. Testosterone reached maximal levels during the mating stage when female-male aggression was most common, and increased slightly, but significantly, during the nesting stage when female-female aggression was most common. However, fighting females had significantly lower T, but higher E₂ and P₄, than non-fighting females. It remains unclear whether these changes in hormone levels during aggressive interactions are a cause or a consequence of a change in behavior. Our results support the “challenge hypothesis”, but suggest that E₂ and/or P₄ may increase in response to aggressive challenges in females just as T does in males. Females may be rapidly aromatizing T to elevate circulating levels of E₂ during aggressive interactions. This hypothesis could explain why non-fighting females had slightly elevated baseline T, but extremely low E₂, during stages when aggressive interactions were most common. Although P₄ increased rapidly during aggressive encounters, it is unclear whether it acts directly to affect behavior, or indirectly via conversion to E₂. The rapid production and conversion of E₂ and P₄ may be an important mechanism underlying female aggression in vertebrates.     

Thermal biology of eastern box turtles in a longleaf pine system managed with prescribed fire

Fire can influence the microclimate of forest habitats by removing understory vegetation and surface debris. Temperature is often higher in recently burned forests owing to increased light penetration through the open understory. Because physiological processes are sensitive to temperature in ectotherms, we expected fire-maintained forests to improve the suitability of the thermal environment for turtles, and for turtles to seasonally associate with the most thermally-optimal habitats. Using a laboratory thermal gradient, we determined the thermal preference range (T_set) of eastern box turtles, Terrapene carolina, to be 27–31 °C. Physical models simulating the body temperatures experienced by turtles in the field revealed that surface environments in a fire-maintained longleaf pine forest were 3 °C warmer than adjacent unburned mixed hardwood/pine forests, but the fire-maintained forest was never of superior thermal quality owing to wider T_e fluctuations above T_set and exposure to extreme and potentially lethal temperatures. Radiotracked turtles using fire-managed longleaf pine forests maintained shell temperatures (T_s) approximately 2 °C above those at a nearby unburned forest, but we observed only moderate seasonal changes in habitat use which were inconsistent with thermoregulatory behavior. We conclude that turtles were not responding strongly to the thermal heterogeneity generated by fire in our system, and that other aspects of the environment are likely more important in shaping habitat associations.     

Amino acid sequence of the active site of human pseudocholinesterase

The usualE ₁ ^u and atypicalE ₁ ^a human pseudocholinesterases (acylocholine acylhydrolase, EC 3.1.1.8) were purified to homogeneity. The active-site serine residue was conjugated with diisopropyl fluorophosphate and digested with trypsin. The tryptic peptide containing the active site was isolated by gel filtration followed by two-dimensional paper chromatography and electrophoresis. The amino acid sequence of the active site peptide obtained from the usualE ₁ ^u enzyme was found to be Gly-Glu-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu. A remarkable structural homology exists between the human and the horse enzymes in their active sites. From the difference in electrophoretic mobility of the active-site peptides obtained from the usual and atypical enzymes, the probable structure of the atypical human enzyme was deduced as Gly-His-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu.     

Thermal relationships between body temperature and environment conditions set upper distributional limits on oviparous species

We determined the thermal biology of the oviparous Liolaemus boulengeri and the viviparous Liolaemus lineomaculatus populations localised at high and low latitude sites in Patagonia, Argentina. We present data of body temperatures in the field (T_b) and preferred temperature in the laboratory (T_pref), micro-environmental and operative temperatures and the effectiveness of thermoregulation. Liolaemus boulengeri and L. lineomaculatus choose different heat sources for active selection of suitable thermal micro-environments for thermoregulation, and the oviparous L. boulengeri is a more effective thermoregulator (E=0.55) than the viviparous L. lineomaculatus (E=0.43). Even when L. boulengeri is a better thermoregulator and both species show identical timing in the reproductive cycles, there are constraint factors that impose limitations on the southernmost distribution of the oviparous L. boulengeri.     

Characterization of a cytosolic estrogen receptor and its up-regulation by 17β-estradiol and the xenoestrogen 4-tert-octylphenol in the liver of eelpout (Zoarces viviparus)

Estrogen binding activity was revealed in the cytosolic fraction of hepatic extracts from adult male and female eelpout (Zoarces viviparus). The binding moiety was characterized by a single class of high affinity binding sites (K_d=0.59±0.05 nM in males and 1.06±0.10 nM in females). The affinity was significantly higher in males. Binding sites were satiable and binding capacity was significantly elevated in vitellogenic females (2.92±0.28 pmol/g) compared to males (1.67±0.11 pmol/g). The binding was specific to known estrogens but not to other tested steroids. The binding moiety was able to bind to DNA–cellulose and was extractable by high salt concentrations. A time-course study of estrogen binding activity in liver cytosol and of vitellogenin (Vtg) in plasma, after intraperitoneal (i.p.) injections of 17β-estradiol (E₂) in male eelpout, was carried out. It was shown that both are inducible by E₂. Estrogen binding activity was significantly elevated 48 h and Vtg 72 h after E₂ treatment. The binding moiety was hereafter designated as a cytosolic estrogen receptor (ER). The estrogenicity of 4-tert-octylphenol (OP) was evaluated by measuring ER and Vtg after i.p. treatment. OP-treatment increased both receptor levels and Vtg concentrations in male fish, indicating that OP acts as an estrogen in male eelpout.     

Ovarian development and serum sex steroid and vitellogenin profiles in the female cultured sturgeon hybrid, the bester

Changes in serum levels of estradiol-17/J (E₂), testosterone (T), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and vitellogenin (VTG), in cultured adult female bester were examined in relation to ovarian development during a 1-year sampling period. Considerable variations in oocyte development were found among fish. Oocytes at previtellogenic stage (≥0–6mm in diameter) generally started to develop concomitantly with the degeneration of the first batch of oocytes. In vitellogenic individuals, ovaries were comprised of more advanced oocytes with diameter ranging from 0–6 to 2–6 mm and in the post-vitellogenic class, oocytes attained their largest size (>2–6mm) while the germinal vesicle was migrating towards the animal pole. Oocytes with a migrating nucleus were maintained during the winter period and massive degeneration started in April–May without germinal vesicle breakdown (GVBD) or ovulation occurring. Seasonal changes in E₂, T and VTG levels were well correlated with the advancement of oogenesis. Their levels increased during vitellogenesis, whereas in the post-vitellogenic (migratory nucleus) stage the levels of E₂ declined from 2–4 ng ml ^?1± to 1–2 ng ml ^?1 and VTG from 4–10 mg ml ^?1 to 0.–0.5 mg ml ^?1 while T levels remained high (50–60 ng ml ^?1). In contrast, serum levels of 17,20?-P were constantly low (less than 0.2 ng ml^?L) throughout the reproductive cycle. These results indicate that the time appropriate for induction of artificial reproduction would be from October–November to April–May when the oocytes are in the late Stages of the development.