Causes of the skewed sex ratio in the Critically Endangered Formosa landlocked salmon of Taiwan

Abstract

The residual estrogenic pollutant alkyl phenols, 4-nonylphenol (NP), 4-tert-octylphenol (OP), and the sex ratio of Formosa landlocked salmon Oncorhynchus formosanus were surveyed in the Formosa landlocked salmon ecological reservation area. This species survives as a remnant, landlocked population in the headwaters of the Chichiawan Stream, a tributary of the Tachia River of central Taiwan. Dams restrict the movement of fish in and out of the agriculturally influenced zones. Fish (n = 157) were collected from a total of 9 habitat sites, and the amount of NP and OP present in each site (ambient water from rearing pools, streams, stream sediments, and agricultural effluents) was measured and the sex of the fish was determined via a noninvasive PCR-based method. The results indicate significantly higher NP content and a skewed sex ratio in Formosa landlocked salmon found in agricultural zones compared to salmon found in non-agricultural zones. The concentrations and distributions of NP observed in this study are ecologically significant because they correspond with the skewed sexual ratio and the lower quality and quantity of male salmon sperm observed in previous field investigations. Although the skewed sex ratios are likely a reflection of multiple endocrine disrupting compounds rather than simply NP and OP alone, these results support the contention that exposure of Formosa landlocked salmon to environmentally persistent estrogenic chemicals can have deleterious reproductive consequences.