Examination of Thiamine Deficiency and Water Quality as Potential Causes of Smallmouth Bass Decline in the Susquehanna River

Elaine Langone Center, Forum

In 2005, abnormalities and increased mortality were first observed in young of the year (YOY) Smallmouth bass (Micropterus dolomieu) (SMB) in the lower reaches of the Susquehanna River including the Juniata River. Since then, both YOY and adult populations have remained surprisingly low, with little indication of rebound. Despite considerable investment of effort and resources, causes of the problem remain inconclusive and likely point to multiple interacting stressors within the ecosystem. We evaluated the hypothesis that the limitation of dietary thiamine (B1) negatively impacted the health of SMB populations. We characterized a suite of thiamine forms (free thiamine and phosphorylated thiamine) in adult and YOY SMB at sites varying in anthropogenic activity within the Susquehanna River watershed. We also conducted visual assessments to evaluate if thiamine status correlated to the intensity of fish abnormalities. Young-of year SMB were further assessed for dietary thiaminase activity, an enzyme known to degrade thiamine. Neither thiaminase activity nor thiamine status significantly correlated to the extent of physical abnormalities. Nevertheless, various metrics of water quality including phosphorus and suspended sediment were highly correlated to thiamine status and identity (phosphorylated versus free thiamine). These results suggest that while thiamine limitation may not directly impact SMB populations, there is a potentially strong link between watershed activities and overall nutritional status. More studies are needed to assess the ecological significance of these patterns.