Reproduction, Life History, and Diets of the Greenthroat Darter Etheostoma lepidum in Low-Flow and High-Flow Environments
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The Greenthroat Darter Etheostoma lepidum (Class Actinopterygii) is a member of the Austroperca complex, along with five other darters found primarily in the Rio Grande drainage of USA and Mexico. Greenthroat Darter, however, is the most widely distributed Austroperca and found east of the Rio Grande drainage into the Edwards Plateau region of central Texas. Threats, as with other aquatic organisms found in arid and semi-arid environments, include natural and anthropogenic modifications to stream flow and water permanency. Purpose of this study was to gain a better understanding of the mechanisms related to low flows and population viability of stream fishes. Using Greenthroat Darters as a representative of the understudied Austroperca complex, study objectives were to quantify life history traits, reproduction, and diets of the Greenthroat Darter and to assess the effects of low flow on their reproduction and diets. Greenthroat Darters were sampled monthly for one year from two environments within the Comal River (Comal County, TX): a low-flow environment, where stream flows were reduced because of a downstream dam and consisted of a persistent low-flowing (0.1 m3/s) pool mesohabitat; and a high-flow environment, where stream flows are sufficient (2.6 m3/s) to maintain a typical riffle mesohabitat for Greenthroat Darters. Study results demonstrated Greenthroat Darters had an 11-month spawning season from October through August, produced multiple batches of ova during the spawning season, lived up to 2 years, and consumed primarily aquatic insects. Differences between flow environments consisted of greater parasite prevalence, lower fish condition, and fewer food items consumed in the low flow environment compared to the high flow environment. However, energy invested into reproduction (i.e., gonadosomatic index, batch fecundity) was not detected between the low flow and high flow environments. Despite greater number of parasites and lower condition, Greenthroat Darters have persisted in the low flow environment since the construction of the dam (late 1800s). Therefore, there is uncertainty among the linkages between typical measures of fish health (e.g., number of parasites, condition) and population viability.