We developed a foraging model for young fishes that incorporates handling and digestion rate to estimate daily food consumption. Feeding trials were used to quantify functional feeding response, satiation, and gut evacuation rate. Once parameterized, the foraging model was then applied to evaluate effects of prey type, prey density, water temperature, and fish size on daily feeding rate by age-0 (19–70 mm) pallid sturgeon (Scaphirhynchus albus). Prey consumption was positively related to prey density (for fish >30 mm) and water temperature, but negatively related to prey size and the presence of sand substrate. Model evaluation results revealed good agreement between observed estimates of daily consumption and those predicted by the model (r2 = 0.95). Model simulations showed that fish feeding on Chironomidae or Ephemeroptera larvae were able to gain mass, whereas fish feeding solely on zooplankton lost mass under most conditions. By accounting for satiation and digestive processes in addition to handling time and prey density, the model provides realistic estimates of daily food consumption that can prove useful for evaluating rearing conditions for age-0 fishes.

This study documented brown trout (Salmo trutta) spawning locations, redd construction timing, and associated environmental variables in an 850-m long mainstem section and a 400-m long diversion channel of Spearfish Creek within the city limits of Spearfish, South Dakota, USA in 2019. The first redds were observed on October 15, with no new redds observed after November 12. Redd construction peaked during the first week of November, when 23 redds were observed in the mainstem section and 50 in the diversion channel. Substrate size was significantly smaller, water temperatures significantly higher, and water velocities significantly greater in redd versus non-redd locations in both the mainstem reach and the diversion channel (P < 0.05). Six significant redd hotspots were observed in the diversion channel. Hotspots were associated with a small (0.1˚C), but significant, increase in water temperature from the rest of the channel locations. This is the first study to document redd locations in Spearfish Creek and will provide a baseline to evaluate future spawning activity, particularly as it may be affected by likely future anthropogenic changes potentially affecting the stream environment.

No abstract

To evaluate the effects of water hardness on survival to hatch of eyed rainbow trout Oncorhynchus mykiss eggs during iodophor disinfection, hard (300 mg/L CaCl 2 ) and soft water (20 mg/L CaCl 2 ) solutions were used in combination with iodophor treatments of 0, 100, 200, 400, 800, and 1600 mg/L. Water hardness did not significantly influence egg survival-to-hatch. In addition, there was no significant interaction between water hardness and iodine concentration on egg survival. However, significant differences in egg survival due to iodine concentration were observed. Egg survival significantly decreased at 800 mg/L, with near complete mortality occurring at 1,600 mg/L. Rainbow trout eyed egg disinfection using iodine concentrations of 800 mg/L or greater are not recommended, regardless of water hardness (calcium) concentrations.