Nitrogen Excretion in Fed and Fasted Lake Sturgeon

Abstract

AbstractLake sturgeon Acipenser fulvescens are imperiled throughout their native range, and hatchery‐reared fish are often stocked to facilitate population restoration. However, the rearing of hatchery fish requires knowledge of nitrogenous excretion rates for efficient culture system design and maintenance. Total ammonia nitrogen (TAN) and urea nitrogen (UN) excretion rates were quantified in age‐0 lake sturgeon that were either fasted or fed brine shrimp Artemia spp. In the first experiment, fish of three different size‐classes (small [10–20 g], medium [50–65 g], and large [100–120 g]) were fasted for 5 d, and their nitrogenous excretions were measured at the end of this period. In the second experiment, lake sturgeon from different size‐classes were fed low (0.5% of body weight [BW] on a dry‐matter basis, 4.2% BW on a wet‐weight basis), and high (1% BW on a dry‐matter basis, 8.3% BW on a wet‐weight basis) rations of Artemia. No UN was detected in fasted lake sturgeon. Endogenous TAN excretion rates varied inversely with fish size. The mean endogenous TAN excretion rate in fasted small lake sturgeon (37.42 mg·kg−1·d−1) was significantly higher than the TAN excretion rates in medium (13.72 mg·kg−1·d−1) and large (6.02 mg·kg−1·d−1) fish. The mean TAN excretion rate in fed small fish (117.34 mg·kg−1·d−1) was significantly higher than the rates in medium (33.69 mg·kg−1·d−1) and large (26.29 mg·kg−1·d−1) fish. Ration size did not significantly affect TAN excretion rates, and mean UN excretion rates in fed fish were not significantly affected by either fish size or ration size. These results suggest that lake sturgeon, like most teleost fishes, predominantly excrete ammonia. The estimates for nitrogen excretion from this study will aid in determining rearing densities for juvenile lake sturgeon in culture systems.