“Xenotoca” doadrioi is a species of viviparous teleost fishes in the Goodeidae family endemic to shallow freshwater ecosystems of the central Mexican plateau and the western Great Basin of the United States. The Goodeidae family is the most diverse and threatened family of teleost fishes in Mexico with 83% considered threatened or endangered. X. doadrioi are critically endangered and in danger of extinction, with declining populations in the wild and an estimated range of only 12-88 km2. According to the IUCN, the main threat X. doadrioi faces is water pollution through agricultural sources. X. doadrioi is a candidate for stock enhancement projects similar to other closely related endangered and extinct in the wild species such as Skiffia francesae and Zoogoneticus tequila.
The goal of this project was to determine how an anthropogenic agricultural runoff contaminant impacts the evolutionary unique form of viviparous reproduction and offspring output of X. doadrioi. Three concentrations of nitrates were tested: 0 mg/L NO3 (no nitrate pollution), 10 mg/L NO3 (low nitrate pollution), and 100 mg/L NO3 (high nitrate pollution). Reproductive data (estimated length of gestation periods, number of birthing events, number of offspring birthed, survivability, and deformity rates) were measured over a six-month sampling period. Additionally, growth rates of adults and offspring were also sampled monthly.
Impacts on reproduction and offspring output were predicted to be more significant in the higher concentrations of nitrates. After two months, the length (mm) and weight (mg) of offspring were significantly less (p < 0.01) in higher concentrations of nitrates, with offspring in the 100 mg/L weighing less than they did at birth. It was also observed that fewer offspring were produced, survival rates were decreased, and both gestation periods and deformity rates increased. These results suggested that offspring exposed to high concentrations of nitrates are being affected most severely. This project provides insights into how wild populations and future generations are affected by nitrates, which can help guide restoration efforts for this critically endangered species.