Current Velocity and Flow Mediated Diets of Larval Fishes
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Purposes of this study were to test two theories relating to food consumption of larval stream fishes. Flow-pulse feeding theory states that larval fish food consumption will be greater following nutrient-rich flow pulses. Drift-feeding theory states that larval fishes enter the drift at night to consume food items under the protection of darkness. Objectives of this study were to quantify gut fullness and occurrence and abundances of food items consumed among larval fishes taken during subsistence flow, base flow, and several high flow pulse tiers (e.g., one per season, one per year) and between larval fishes taken during the day in slackwater habitats and larval fishes taken during the night in swift water habitats. During a one year period of observation among four sites and two rivers, mesolarval of obligate riverine taxa (i.e., Cyprinidae, Catostomidae, Percidae) had greater gut fullness within 28 d following a 1 per season flow event than those taken within 28 d following subsistence flow, base flow, 2 per season flow event. Greater gut fullness during a 1 per season flow event was attributed to greater numbers of copepods and detritus consumed. However, gut fullness and occurrences and abundances of food items consumed by metalarvae were independent of flow. Among mesolarvae and metalarvae collectively and among taxa, gut fullness was greater during the day for fishes taken in slackwater habitat than those taken at night from swift water habitats. Larval fishes within lowland rivers of western gulf slope drainages of Texas conformed only partially to larval fish feeding theories. Drift-feeding theory likely is not a mechanism to explain larval drift at night, and the value of flow pulses to larval fish feeding and subsequent recruitment was not consistent among larval life stages. Nevertheless, this study documents for the first time larval fish food consumption in lowland rivers and establishes a process to quantify the value of flow tiers relevant to the stream fish community.