Effect of Turbidity on Survival and Growth of Juvenile Devils River Minnow (Dionda diaboli) Fed Chironomid Larvae

The Devils River Minnow (Dionda diaboli) is a federally endangered species endemic to spring-fed tributaries of the Rio Grande drainage of Mexico and western Texas. Its occurrence in spring-fed stream habitats suggests that increased turbidity could negatively affect its survival in the wild. We used a laboratory experiment to assess the effect of turbidity (0 NTU: control; 10 NTU: low; 50 NTU: moderate; and 100 NTU: high) on time to initiate foraging, feed conversion ratio (FCR), specific growth rate (SGR), and condition coefficient for juvenile D. diaboli fed on a diet of chironomids, a pollution-tolerant invertebrate. Our results showed that increased turbidity significantly affected time to initiate foraging, but not the amount of food consumed, growth, body condition, and survival. Thus, although short-term exposure to turbidity conditions negatively affected feeding behavior, the treatments were not sufficient to cause significant differences in physiological performance and growth, suggesting D. diaboli may be resistant to short-term pulse increases in turbidity in its natural habitat. In this study, D. diaboli fed on chironomids had low average juvenile survivorship (27%) by the end of 12 weeks, with decreased growth and weight beginning by week 4 and 6, respectively. Thus, although increased turbidity did not directly affect D. diaboli, if elevated turbidity causes alteration of food resources toward pollution-tolerant macroinvertebrates, the species could be negatively affected. These results provide important information on the impacts of turbidity on the long-term conservation of D. diaboli, though further studies are needed to examine the species response to combined impacts of turbidity, droughts, non-native species invasions, and altered habitat.