Effects of the Herbicide Pendimethalin on Hormone Receptor Expressions and Dorsal Fin Biometrics in Thai Medaka, <I>Oryzias Minutillus</I> (Actinopterygii: Beloniformes: Adrianichthyidae)

Abstract

Ngamniyom A., Panyarachun B. 2012. Effects of the herbicide pendimethalin on hormone receptor expressions and dorsal fin biometrics in Thai medaka, Oryzias minutillus (Actinopterygii: Beloniformes: Adrianichthyidae). Acta Ichthyol. Piscat. 42 (3) 239-246.Background. Xeno-oestrogens have negative effects on the endocrine systems of wildlife including freshwater fish. Pendimethalin is a herbicide found in the environment which exerts some oestrogenic action in vivo. Dwarf medaka (known also as Thai medaka), Oryzias minutillus Smith, 1945, inhabit the natural aquatic environments. Dorsal fin of this species is a secondary sex character controlled by sex hormones and assumes as a sensitive bioindicator for testing of oestrogenic chemicals. In this study, we aimed to examine the pendimethalin effects on hormone receptor expressions and dorsal fin biometrics in adult Thai medaka. Materials and methods. Pendimethalin effects on the androgen receptor (AR) and estrogen receptor (ER) β expressions in dorsal fins were determined by semi-quantitative RT-PCR. The fin biometry was presented as the values (%) of the dorsal fin length (DFL) divided by the standard length (SL).Results. In males, AR levels decreased when the fish were exposed to 0.1 µg · mL -1 pendimethalin for 60 days and were exposed to 1 µg · mL -1 for 30 and 60 days. In females, a 60-day treatment with 1 µg · mL -1 caused AR levels to decrease. Conversely, in males, ERβ levels increased after 30 and 60 days of treatment with 1 µg · mL -1 . In females, ERβ levels increased after 30 days of treatment with 1 µg · mL -1 and 60 days of treatment with 0.1 µg · mL -1 . In males, values of DFL/SL% decreased after exposure to 1 µg · mL -1 for 60 days. Additionally, we observed 4 testis-ova among 30 gonads from males treated with 1 µg · mL -1 for 60 days. Conclusion.Our results suggest that pendimethalin may interfere with endocrine processes via hormone receptors, leading to the feminisation of dorsal fins and gonads in Thai medaka.

Molecular analysis of population and De Novo transcriptome sequencing of Thai medaka, Oryzias minutillus (Teleostei: Adrianichthyidae)

“…Recently, Smitthikunanon et al (2009) originally determined the molecular phylogeny of Thai medaka from twelve localities that were based on the displacement loop (D-loop) region of mitochondrial DNA (mtDNA), suggesting that this marker was potentially able to be used for the Thai medaka population. However, molecular data are needed to evaluate for Thai medaka, and studies of the Thai medaka populations have been remained to examine (Ngamniyom et al, 2009;Ngamniyom and Panyarachun, 2012).…”

Investigation of hormone receptor expressions in the fins of Oryzias woworae (Actinopterygii: Beloniformes: Adrianichthyidae)

“…The anal fin of the male plays a role in mating with the female for successful fertilisation (Koseki et al 2000). Moreover, the dorsal and anal fins have been used as bio-indicators for examination of endocrine disrupting chemicals (Hayashi et al 2007, Ngamniyom andPanyarachun 2012).…”