Search

Because blood vitellogenin (Vg) has been considered a biomarker for environmental estrogens, the basal levels of Vg and 17β-estradiol (E2 ) were determined in male Japanese whiting reared under natural conditions. Serum levels of Vg and E2 were measured and gonadal development was assessed by gonadosomatic index (GSI) and histological observation in 8–10 male fish at monthly intervals throughout the annual reproductive cycle. Serum E2 was <60 pg/mL throughout the study period. In contrast, serum Vg exhibited seasonal changes: serum levels of Vg gradually increased from April to May (mean 63 ± 13 ng/mL and 124 ± 48 ng/mL in April and May, respectively), and then reached a peak value (mean 352 ± 68 ng/mL) in June. Thereafter, serum Vg gradually decreased, reaching undetectable levels (<50 ng/mL) in October. Serum levels of Vg tended to increase in the male fish in which the GSI was >1%. Histological observation revealed that testes in such male fish were in active spermatogenesis and then all of the testes of male fish in which serum Vg decreased to ND levels were regressed. These results suggest that Vg productive potency (sensitivity to estrogens) may increase in the spermatogenic stage, resulting in production of Vg in response to very low levels of natural or xenobiotic estrogens. [ABSTRACT FROM AUTHOR]

ABSTRACT: To determine the thermal limit for normal spawning of Japanese whiting and to evaluate thermal effects on spawning in the normal temperature range, two experiments were conducted. In Experiment 1, the temperature of three experimental groups (Groups A, B and C) was increased from 25 to 28, 31 or 33°C, respectively. Subsequently, temperatures in all groups were decreased to 28°C. During the experimental period, the number of eggs, egg size, and hatching rate were monitored. According to the results, the upper thermal limit of normal spawning was considered to be 28–29°C, because the number of eggs and the hatching rate decreased at temperatures over 28°C. However, egg size tended to be reduced at 28°C, and was found to be strongly dependent on temperature. In Experiment 2, the number of eggs, egg size and time of spawning were compared between fish held at a constant temperature of 22°C (Group CT) and those held at increasing temperatures from 22 to 28°C (Group IT). Group IT spawned more in number and had smaller-sized eggs than did Group CT, while spawning was delayed in group IT. To identify the thermal effects on spawning of Japanese whiting, the mechanisms governing egg size must be determined. [ABSTRACT FROM AUTHOR]

We previously demonstrated the biological activities of single-chain recombinant gonadotropins (scGTHs) of goldfish Carrassius auratus follicle-stimulating hormone (scFSH) and luteinizing hormone (scLH), produced by a baculovirus–silkworm larvae system, by using in vivo bioassays with some fishes including Japanese eel Anguilla japonica. Among the bioassays, we succeeded in induction of spermatogenesis of sexually immature male Japanese eels by both scFSH and scLH, especially resulting in the occurrence of spermatozoa in scLH-administered males. However, those recombinant hormones did not induce enlargement of testes. In order to further confirm the potency of recombinant GTHs for use in aquaculture species, we administered scFSH and scLH to males of Japanese eel at higher dosage and frequency (eight times with 2–5 days interval) than those of the previous study (five or six times with 7 days intervals), including combination of scFSH and scLH administration (scFSH–scLH). Gonadosomatic indices (GSI) of scLH- and scFSH–scLH-administered males were larger than those of initial control males and of control males that were injected with saline. Enlargement of testes was also confirmed by measurement of testicular lobe size in scFSH-, scLH-, and scFSH–scLH-administered males. By histological observation, occurrence of spermatozoa was confirmed in scLH- and scFSH–scLH-administered eels. Although milt production was not induced, higher dosage and frequency of scGTH administration was effective in promoting testicular development of immature eels. Thus, single-chain fish GTHs produced by the baculovirus–silkworm larvae system could be a useful tool for promotion of gonadal maturation in aquaculture fishes. [ABSTRACT FROM AUTHOR]

Abstract: Recombinant gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) of goldfish Carassius auratus were previously produced by baculovirus in silkworm larvae Bombyx mori. These GTHs are heterodimeric hormones consisting of a common α subunit and an FSHβ or LHβ subunit; the GTH subunits were produced separately in silkworm larvae. In order to simplify the production process of the hormones and increase production efficiency, we produced single-chain FSH (scFSH) and LH (scLH) in which the FSHβ or LHβ subunit was fused to the α subunit. Biological activities of these single-chain GTHs produced by baculovirus–silkworm larvae system were analyzed in vivo using male goldfish, female bitterling Rhodeus ocellatus ocellatus, and male Japanese eel Anguilla japonica. Injection of hemolymph containing scFSH or scLH induced milt production in male goldfish. scLH induced ovulation in bitterling but scFSH showed lower potency. Both scLH and scFSH induced the initiation of spermatogenesis in the testes of sexually immature male eels after 5–6 administrations of the recombinant GTHs at seven day intervals. Spermatozoa were observed in scLH-administered eels and spermatids in scFSH-administered eels whereas the testes of eels administered with hemolymph of untreated silkworm larvae remained at the spermatogonia stage. Thus, single-chain GTHs of goldfish produced by baculovirus in silkworm larvae showed in vivo biological potency not only in the final phase of gametogenesis (milt production and ovulation) but also in the early phase of gametogenesis (spermatogenesis). We suggest that single-chain fish GTHs could be used for the induction of gonadal development in aquaculture fishes. [Copyright &y& Elsevier]

Surveys of the estrogenic activity in coastal areas of Japan were performed by using two serum vitellogenins (Vg-530 and Vg-320) of male Japanese common goby Acanthogobius flavimanus as biomarkers. To evaluate the relationship between the Vg concentrations in the serum of male fish and the concentrations of environmental estrogens in seawater, 3 week exposure experiments were performed using estradiol (E2), nonylphenol (NP) and bisphenol A (BPA). From the results of the E2 exposure, mean concentrations of the Vg and the ratio of Vg-positive fish increased from actual concentration at 10.5 ng/L E2 treatment. Exposure of NP and BPA showed that the 19.0 µg/L NP treatment induced the Vg but 133.7 µg/L BPA did not. As for the survey of the estrogenic activity in coastal areas, the mean Vg concentrations and ratio of Vg-positive fish in some urban areas were similar to values of the 10.5 ng/L E2 treatment. Although E2 and NP were detected in the seawater from urban areas, the concentrations were concluded as not sufficient to independently induce the Vg. Considering these results, it is concluded that the total estrogenic activity in some urban areas is dependent not only on E2 but synergistically with other environmental estrogens. [ABSTRACT FROM AUTHOR]

Two vitellogenins (Vgs) were detected in serum from estradiol-17β (E2)-injected Japanese common goby (Acanthogobius flavimanus). Vitellogenins with molecular masses of 530 kDa (Vg-530) and 320 kDa (Vg-320) were purified, and used to raise specific antisera in rabbits. Sandwich enzyme-linked immunosorbent assays (ELISAs) for Vg-530 and Vg-320 were developed using the antisera and the isolated Vgs. The sensitivity ranges of these ELISAs were 1.25–160 ng/ml for Vg-530 and 0.26–66 ng/ml for Vg-320, and very low cross-reactivity was found with the alternate Vg in each assay. Treatment of male gobys with E2 by injection and immersion induced both Vgs in sera in a dose-dependent manner. The mean concentrations of the Vgs increased from 10 ng/L E2 exposure for three weeks. Serum concentrations of the two Vgs in field-collected maturing females increased in accordance with increment of E2 level and ovarian development, and the mean concentrations of Vg-530 were higher than those of Vg-320 in maturing female. These results indicate that the sandwich ELISAs for Vg-530 and Vg-320 developed in the present study is useful as an assay system for surveys of estrogenic activity in coastal areas of Japan. [Copyright &y& Elsevier]