Age, Growth, and Reproductive Biology of Buffalofishes (Ictiobus spp.) in the lower Red River catchment

Abstract

Many North American freshwater fishes are of conservation concern. Riverine non-game fishes are understudied with many knowledge gaps in life history such as factors influencing spawning, hatching, and growth of individuals. Buffalofishes, such as Bigmouth Buffalo Ictiobus cyprinellus, Black Buffalo I. niger, and Smallmouth Buffalo I. bubalus are emblematic of these conservation concerns and knowledge gaps. My research objectives were to relate environmental covariates to adult buffalo growth and assess population demographics of three sympatric buffalofishes and determine the hatch and spawning chronology of female buffalofishes in the lower Red River catchment. I aged 598 Bigmouth, 343 Black, and 1,153 Smallmouth Buffalo that were sampled from March 2022 to May 2024 using gillnets and boat electrofishing. I collected gonadosomatic index from 565 females and then used the ovaries for histological analyses. Additionally, I collected 67 age-0 buffalofishes using mini-fyke nets, beach seine, and a Siamese trawl. On average, Black Buffalo and Bigmouth Buffalo were larger than Smallmouth Buffalo. The oldest individual was a 61-year-old Bigmouth Buffalo. My results indicate low mortality and variable recruitment among species with Bigmouth Buffalo having the least stable recruitment Successful hatches were positively associated with precipitation, while environmental factors such as air temperature and discharge variability influenced post-ovulatory follicle presence. Juvenile hatch success varied across years and locations, with Smallmouth Buffalo showing the longest spawning period and Bigmouth Buffalo and Black Buffalo having more restricted timelines. These results suggest an opportunistic spawning strategy with limited successful hatches during the warmwater season, emphasizing the need for winter sampling to capture coldwater season dynamics.