Examination of Bigheaded Carp Ovaries Indicates Batch Spawning

Abstract

Fishes utilize several different species-specific reproductive strategies adapted to their environment. Invasive species may display reproductive strategies that allow successful reproduction in varying environments, such as batch and protracted spawning. Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, referred to as bigheaded carp, are invasive species that have been introduced worldwide. In some invaded ranges, they either have a protracted spawning period and/or spawn multiple times in a season, which can be advantageous in novel environments. Reproductive strategies can vary between river systems or with environmental conditions, and understanding differences in strategies can improve management of bigheaded carp. To determine reproductive strategy, we evaluated the histology of spawning capable ovaries from Silver Carp (n = 58) and Bighead Carp (n = 38) collected during May-September 2016 and June 2017 from Pools 17-20 of the upper Mississippi River (UMR). We found that 87.9% of Silver Carp (n = 51) and 86.8% of Bighead Carp (n = 33) had an ovary that contained primary growth, cortical alveolar, and vitellogenic oocytes simultaneously. Multiple stages of oocytes within an ovary indicated that individuals were capable of spawning multiple times during a single year, and the presence of postovulatory follicle complexes demonstrated that individuals had already spawned while oocytes were still present. Based on histological samples, bigheaded carp appear to be indeterminate batch spawners, with oocytes continuing to develop throughout the spawning period. Silver and Bighead carp in the UMR may exhibit protracted and batch spawning and employ flexible spawning strategies among different river systems, which can increase the probability of successful recruitment in a variable environment.Fish species display several types of reproductive strategies, including total or batch spawning, determinate or indeterminate fecundity, and synchronous, groupsynchronous, or asynchronous spawning, which have evolved in response to varying environmental conditions. Certain spawning strategies may be advantageous and contribute to the success of a species. For example, total spawners, which are always determinate spawners with

Light Trapping Reveals Multiple Bigheaded Carp Spawns Upstream of Lock and Dam 19 in the Upper Mississippi River

“…2019); however, mature bigheaded carp are routinely collected by commercial fishers upstream of LD19 (Lenaerts 2019; Lenaerts et al. 2021a, 2021b, 2021c, all this special section). Native and introduced fishes have been documented passing upstream through many LD structures in the upper Mississippi River (Tripp et al.…”

Plasticity in Reproductive Potential of Bigheaded Carp along an Invasion Front

“…The subsamples were enumerated under a stereo dissecting microscope (magnification of 0.75× and WF10× eye piece magnification). The Silver Carp and Bighead Carp had several egg stages within a sample, indicating multiple spawning events within a season (this finding was confirmed via histology in Lenaerts et al., in press), and the most developed eggs (i.e., late‐stage vitellogenic oocytes) within each subsample were counted to yield batch fecundity. Only the most developed eggs were used in the following analyses.…”

“…There is evidence of protracted and multiple spawning in invaded environments, as indicated by multiple oocyte sizes within an ovary (Schrank and Guy 2002; Papoulias et al. 2006; Lenaerts et al., in press [this special section]) and egg collections over several months (Coulter et al. 2013; Lenaerts et al.…”

A Quick Method for Estimating Batch Fecundity in Bigheaded Carp

“…2020; Lenaerts et al. 2021a). Therefore, batch fecundity only represents the number of eggs that Silver Carp are capable of releasing during a single spawning event (Hunter et al.…”

“…Various egg developmental phases were evident within spawning capable ovaries (Lenaerts et al. 2021a, this special section); therefore, only the eggs representing the largest developmental phase in each sample—presumed to be the most mature at the time of removal—were counted, yielding a batch fecundity estimate (number of eggs released in a single spawning event) rather than total fecundity (Hunter et al. 1985).…”