Behavioral and sex ratio modification of Japanese medaka (Oryzias latipes) in response to environmentally relevant mixtures of three pesticides

Abstract

We exposed Japanese medaka (Oryzias latipes) to environmentally relevant concentrations of azinphos-methyl, chlorothalonil, endosulfan, and mixtures of all three to determine if combinations of these pesticides result in additive, less-than-additive, or more-than-additive effects. Medaka were exposed from fertilization until 7 days posthatching, and end points included survival, time to hatch, size at 7 days posthatching, activity level (as measured by distance swam) and foraging ability at 3 weeks posthatching, and adult size, liver size, and sex ratio at 5 months posthatching. Although exposure to individual pesticides or pesticide mixtures did not affect survival, hatching time, or foraging ability, fry exposed to azinphos-methyl were significantly smaller at 1 week of age, and those exposed to chlorothalonil and a combination of the chemicals showed reduced activity. Adult sex ratios were biased toward females in all groups exposed to pesticides, with those exposed to azinphos-methyl, chlorothalonil, and the pesticide mixture departing significantly from an even sex ratio. There was no evidence of additive or synergistic effects of pesticide mixtures.

Risks of carbamate and organophosphate pesticide mixtures to salmon in the Pacific Northwest

“…The high concentrations used in the Laetz et al (2009) mixture studies may have affected secondary, nontarget sites of action, which would not have been affected at environmentally relevant concentrations. Past studies that were designed to determine mixture toxicity at environmentally relevant concentrations (e.g., George et al 2003;Teather et al 2005;Brander et al 2009) did not produce effects beyond those predicted by assuming concentration addition.…”

Endosulfan affects GnRH cells in sexually differentiated juveniles of the perciform Cichlasoma dimerus

“…Reduced GtH neurosecretory activity can lead to delayed sex differentiation, and reduced fecundity; all reported effects of ES action under sub-lethal exposure (ranged from 0.01 to 1.4 μg/L) in fish (Balasubramani and Pandian, 2008;Gormley and Teather, 2003;Shukla and Pandey, 1986). Alterations in germ cell distribution and deviation to female sex proportion have also been reported as sub-lethal effects of the pesticide on larvae (Teather et al, 2005;Willey and Krone, 2001). However, on our previous study on sexually undifferentiated larvae, alterations caused by ES at the hypothalamus and pituitary did not affect the onset of gonadal differentiation at the studied stage of development, 30 days post fertilization (dpf) (Piazza et al, 2011).…”

Endocrine disruptive potential of endosulfan on the reproductive axis of Cichlasoma dimerus (Perciformes, Cichlidae)

“…As is the case with many pesticides, ES has also been suggested as an endocrine disrupting chemical, capable of interfering with the normal functions of the endocrine system of animals (Mills and Chichester, 2005). Evidences for the action of ES on the reproductive axis of fish include: decreased clutch size (Gormley and Teather, 2003) and sex ratio skew toward females (Teather et al, 2005) in exposed Japanese medaka (Oryzias latipes); lowered vitellogenin plasma levels in females (Chakravorty et al, 1992) and altered expression of steroidogenic enzymes, gonad-related transcription factors and cfGnRH mRNAs in larvae (Rajakumar et al, 2012;Chakrabarty et al, 2012) of the Asian catfish (Clarias batrachus); sex ratio skew toward females and delayed sexual maturity following discrete immersion of fry (Balasubramani and Pandian, 2008) and decreased hatching rate, reduced gonadosomatic index in females, vitellogenin levels increase in males and histological gonadal alterations (Han et al, 2011) in exposed zebrafish (Danio rerio).…”