Abstract-There are many endocrine-disrupting chemicals in the environment that have the potential to alter the development of sexual characteristics in fish and wildlife. Little is known about the factors that influence the development of an intersex condition in fish. Japanese medaka (Oryzias latipes) were exposed to octylphenol (OP), a known estrogen agonist, during various life history stages to determine the factors that control induction of testis-ova, an intersex condition. In male medaka exposed to OP (100 g/L) beginning at 1, 3, 7, 21, and 35 d posthatch, the incidence of testis-ova at 100 d posthatch was highest in the 3-d posthatch treatment (4 of 14 males) and declined when exposures were initiated with older fry. Exposure to OP (100 g/L) from hatch for a period of 1 or 2 months did not induce testis-ova, but exposure for 3 months resulted in 3 of 50 males developing this condition. Exposures of adult male medaka to OP (200 and 300 g/L) for either 18 or 36 d resulted in only one testis-ova in a male fish exposed for 36 d to the highest nominal concentration. In addition to testis-ova, male medaka exposed to OP developed testicular fibrosis. Overall, these data indicate that prolonged exposure of male medaka to an estrogen agonist beginning around the period of gonadal differentiation is optimal for the development of testis-ova, but this intersex condition can be induced when exposure begins at later life stages.

There are many endocrine‐disrupting chemicals in the environment that have the potential to alter the development of sexual characteristics in fish and wildlife. Little is known about the factors that influence the development of an intersex condition in fish. Japanese medaka (Oryzias latipes) were exposed to octylphenol (OP), a known estrogen agonist, during various life history stages to determine the factors that control induction of testis‐ova, an intersex condition. In male medaka exposed to OP (100 μg/L) beginning at 1, 3, 7, 21, and 35 d posthatch, the incidence of testis‐ova at 100 d posthatch was highest in the 3‐d posthatch treatment (4 of 14 males) and declined when exposures were initiated with older fry. Exposure to OP (100 μg/L) from hatch for a period of 1 or 2 months did not induce testis‐ova, but exposure for 3 months resulted in 3 of 50 males developing this condition. Exposures of adult male medaka to OP (200 and 300 μg/L) for either 18 or 36 d resulted in only one testis‐ova in a male fish exposed for 36 d to the highest nominal concentration. In addition to testis‐ova, male medaka exposed to OP developed testicular fibrosis. Overall, these data indicate that prolonged exposure of male medaka to an estrogen agonist beginning around the period of gonadal differentiation is optimal for the development of testis‐ova, but this intersex condition can be induced when exposure begins at later life stages.

Polychlorinated diphenyl ethers (PCDEs) are a group of compounds that resemble polychlorinated dibenzofurans in structure that have been detected at ppb concentrations in fish from the Great Lakes. The objective of this project was to determine the toxicological significance of PCDE residues in fish. PCDE congener 77 (3,3Ј,4,4Ј-tetrachlorodiphenyl ether), congener 71 (2,3Ј,4Ј,6-tetrachlorodiphenyl ether), congener 118 (2,3Ј,4,4Ј,5-pentachlorodiphenyl ether), and congener 105 (2,3,3Ј,4,4Ј-pentachlorodiphenyl) were tested for toxicity with early life stages (ELS) of Japanese medaka, Oryzias latipes. These embryotoxicity data showed that the mono-ortho congeners 105 and 118 and the non-ortho congener 77 were embryotoxic to medaka. However, the toxic equivalency factors (TEFs) estimated for congeners 105, 77, and 118 relative to 2,3,7, 8-TCDD were relatively low at 0.00056, 0.00003, and 0.00001, respectively. PCDE compounds were isolated in a fraction prepared from a bulk extract of Lake Ontario lake trout. In this fraction, congeners 99 (2,2Ј,4,4Ј,5-pentaCDE), 153 (2,2Ј,4,4Ј,5,5Ј-hexaCDE), 154 (2,2Ј,4,4Ј,5,6Ј-hexaCDE), and 163 (2,3,3Ј,4Ј,5, 6-hexaCDE) comprised 81.3% of total PCDEs, while congeners 77, 71, 118, and 105 comprised only 1.1% of total PCDEs. The LC50 for embryotoxicity of this fraction was equivalent to 15.5 ng/ml of total PCDEs. Toxicopathic lesions noted in medaka embryos exposed to either individual PCDEs or the lake trout extract included vascular hemorrhage but no edematous lesions. Medaka fry did not exhibit symptoms of hyperexcitability prior to death, as has been noted for ELS of lake trout exhibiting ''swim-up syndrome.'' These data indicate that PCDEs in Lake Ontario lake trout have the potential to induce toxic effects in early life stages of fish. However, the medaka mortalities were not consistent with observations of either ''blue-sac disease'' or swim-up syndrome observed in some natural populations of Great Lakes salmonids.

Abstract-Polychlorinated diphenyl ethers (PCDEs) are a group of compounds that resemble polychlorinated dibenzofurans in structure that have been detected at ppb concentrations in fish from the Great Lakes. The objective of this project was to determine the toxicological significance of PCDE residues in fish. PCDE congener 77 (3,3Ј,4,4Ј-tetrachlorodiphenyl ether), congener 71 (2,3Ј,4Ј,6-tetrachlorodiphenyl ether), congener 118 (2,3Ј,4,4Ј,5-pentachlorodiphenyl ether), and congener 105 (2,3,3Ј,4,4Ј-pentachlorodiphenyl) were tested for toxicity with early life stages (ELS) of Japanese medaka, Oryzias latipes. These embryotoxicity data showed that the mono-ortho congeners 105 and 118 and the non-ortho congener 77 were embryotoxic to medaka. However, the toxic equivalency factors (TEFs) estimated for congeners 105, 77, and 118 relative to 2,3,7, 8-TCDD were relatively low at 0.00056, 0.00003, and 0.00001, respectively. PCDE compounds were isolated in a fraction prepared from a bulk extract of Lake Ontario lake trout.