Factors affecting the development of testis‐ova in medaka, Oryzias latipes, exposed to octylphenol

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 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.

Estrogenic potency of chemicals detected in sewage treatment plant effluents as determined by in vivo assays with Japanese medaka (Oryzias latipes)

“…We have previously observed this condition in medaka exposed to extremely high concentrations of E2 and octylphenol [32]. Intersex was not observed in fish exposed to higher concentrations of this compound.…”

“…Spontaneous reversal of gonadal sex or development of intersex gonads has never been observed in medaka [34], so even the most subtle responses such as the presence of single oogonia must be taken as evidence of effects upon gonadal differentiation. Our recent studies of the factors that affect development of testis-ova in medaka [32] indicated that the optimal conditions for development of this intersex condition in medaka involved starting exposures to estrogenic chemicals within the first week of hatch. This is also the period for optimal induction of complete sex reversals in medaka by exposure to potent estrogens [34].…”

“…This is also the period for optimal induction of complete sex reversals in medaka by exposure to potent estrogens [34]. However, exposures of adult medaka to estrogens can induce testis-ova, even though the incidence is very low [32]. This indicates that bipotential germ cells are present in the gonad of adult medaka that are susceptible to chemically induced alterations to differentiation.…”

Reproductive endocrine disruption in smallmouth bass (Micropterus dolomieu) in the Potomac River basin: spatial and temporal comparisons of biological effects

“…However, the presence of TO, even in adult males, may be more indicative of early life stage exposure, as opposed to induction of Vtg in males or immature fish. Larval stages have been shown to be the most sensitive period of exposure for induction of TO in a number of fish species (Gray et al 1999; Koger et al 2000; Krisfalusi and Nagler 2000; Metcalfe et al 2000; Liney et al 2005). However, there are two windows of enhanced sensitivity to EDC—the larval or yolk sac stage when gonad differentiation occurs and the reproduction period or gonadal recrudescence (seasonal maturation) in mature adults (Ankley and Johnson 2004).…”

Assessing the Sensitivity of Different Life Stages for Sexual Disruption in Roach ( Rutilus rutilus ) Exposed to Effluents from Wastewater Treatment Works

“…Laboratory studies have shown that it is possible to induce gonadal duct disruption and germ cell disruption in early-life-stage (ELS) fish by exposing them to some of the estrogenic chemicals found in WwTW effluent, but generally this occurs only at concentrations higher than those found in the environment (Gimeno et al 1997, 1998; Gray et al 1999; Knorr and Braunbeck 2002; Koger et al 2000; Yokota et al 2000). Our previous work has shown that exposure of roach to an estrogenic WwTW effluent during early life [50–150 days posthatch (dph)] induced VTG synthesis and gonadal duct disruption (feminization) but not the simultaneous presence of male and female germ cells in the same gonad (Rodgers-Gray et al 2001).…”