Reproductive parameters in invasive blue catfish (Ictalurus furcatus) from tributaries of the Chesapeake Bay in Maryland and Delaware, 2020–22

Over the past few decades, Ictalurus furcatus (Valenciennes in Cuvier and Valenciennes, 1840; blue catfish) have become a formidable invasive species in tidal tributaries of the Chesapeake Bay in Maryland and Delaware. Knowledge of their reproductive behaviors can support managers in the determination of ideal timing and implementation of mitigation strategies. In 2020–22, the U.S. Geological Survey sampled blue catfish from the Chesapeake Bay’s tidal reaches of the Nanticoke River, Broad Creek, Marshyhope Creek, and Patuxent River in Maryland and Delaware from March to October. All fish were analyzed with histology to assess reproductive stages (immature, pre-spawn [early and late], and post-spawn). Plasma was collected for multiple endpoints including 17β-estradiol (E2), calcium, and total protein. Results indicated that female spawning generally occurred from late April through June, as evidenced by the histological data showing that the number of vitellogenic oocytes in late pre-spawn females began to increase in April, peaked in May, and gradually declined through July. In males, the greatest number of late pre-spawn individuals was observed in April and gradually declined through June. Additionally, female E2 levels were highest in late, pre-spawn females, thus showing a similar trend as the histological results, indicating that this endpoint can be used for assessing reproductive changes over time. Collectively, this study documents typical spawning patterns in blue catfish within the Chesapeake Bay watershed. However, further research across different watersheds would enhance data availability and inform more comprehensive management strategies.