We developed an index of egg and larval maturation for Lake Sturgeon Acipenser fulvescens to incrementally chart development over time. To evaluate the relationship between temperature and development rate, eggs and larvae from the Wolf River were incubated at four constant water temperatures. The time required for neural tube closure, hatch, and exogenous feeding were monitored. The number of hours from incubation to each development stage and mean water temperature were related by predictive exponential regression equations for neural tube closure (R2 = 0.96), start hatch (R2 = 0.97), end hatch (R2 = 0.97), and exogenous feeding (R2 = 0.99). Calculated hourly development was used to create an index capable of predicting specific daily development. Daily development from incubation to exogenous feeding ranged from 2.0% to 8.3% at 10°C to 19.9°C. This index was used to predict the rate of development of sturgeon eggs and larvae from the St. Lawrence River reared in water with varying temperatures. All development stages occurred within 24 h of the time predicted by the index. This index may be used to accurately predict and manipulate the progress of development and assist with the culture and management of Lake Sturgeon populations.

Contaminants of emerging concern (CECs) are ubiquitous throughout aquatic environments. Previous research has shown that CECs can have detrimental effects on fish biology, potentially leading to population impacts. Specifically, polybrominated diphenyl ethers (PBDEs), a class of CECs, have been shown to alter thyroid hormones in fish, which can impact development, endocrine system functioning, and possibly imprinting. These impacts can lead to reproductive effects and population declines, which have serious implications for species of conservation priority, such as the Lake Sturgeon Acipenser fulvescens. To assess the effects of CECs and PBDEs, Lake Sturgeon were evaluated at rearing facilities within the Great Lakes basin during 2017-2018 to determine (1) whether exposure to CECs and PBDEs differs between facility locations and (2) whether changes in whole-body PBDE concentrations correlate with changes in thyroid hormones (triiodothyronine [T 3 ] and thyroxine [T 4 ]), which could indicate impacts to imprinting. Exposure to CECs and PBDEs differed among sites. The CECs that were detected in water across all sites included atrazine, hexachlorobenzene, N,N-diethyl-meta-toluamide (DEET), desethylatrazine, erythromycin, and metformin, with the highest concentrations (except for DEET) measured at the Maumee River (Ohio) streamside rearing facility.We detected PBDEs in every sample of water, food, and Lake Sturgeon eggs and whole bodies, and there were no differences in lipid-normalized total PBDE concentrations in whole bodies across sites. Concentrations of total PBDE and the PBDE congeners 47, 99, 100, 153, 154, and 209 in fish tissues did not correlate with serum T 3 and T 4 levels, indicating that observed concentrations were unlikely to negatively impact Lake Sturgeon rearing for the biological endpoints assessed. Overall, this study exemplifies a cautionary tale since CECs and PBDEs were identified throughout Lake Sturgeon habitat and in hatchery food sources. Fisheries managers should be aware of the potential for CEC and PBDE impacts even though current observed levels do not seem to be impacting Lake Sturgeon rearing success.

This study evaluated the relationship between temperature and growth rate of juvenile Lake Sturgeon Acipenser fulvescens and determined optimal temperature for growth based on weight gain and length increase. Four temperature regimes (12.0 ± 0.5, 17.0 ± 0.3, 21.6 ± 0.4, and 26.8 ± 0.6°C [mean ± SD]) were tested in triplicate to determine specific growth rates and daily length increases. In addition to growth rate, consumption rates were also assessed by recording the grams of feed offered to fish and the amount uneaten to ensure all fish were fed to satiation. Lake Sturgeon consumed 2.76, 9.63, 13.69, and 14.22% body weight/d, respectively, and grew at a specific growth rate of 0.50, 1.42, 2.01, and 1.75 mm/d, respectively. Fish consumed more food with increasing water temperature; however, daily length increase declined at 26.8°C. This study may be used to construct growth models for production programs, project size at stocking, and project feed rates based on water temperature.