Reproductive Potential of Captive Rio Grande Silvery Minnow

Abstract

Captive propagation and augmentation of the Rio Grande Silvery Minnow Hybognathus amarus is necessary for continued persistence of the species until habitat can be restored. Augmentation occurs using captive fish within the first year (age 0) through age 2; however, older year‐classes (ages 3–4) have been released into the wild. We quantified fecundity and compared egg quality across four reproductive age‐classes (1–4) of hatchery‐reared Rio Grande Silvery Minnow. Batch fecundity (total number of spawned eggs) ranged from 2,029 eggs in age‐1 fish to 10,588 eggs in age‐4 fish. Standing stock of vitellogenic (i.e., yolked) oocytes remaining in ovaries after spawning increased from 988 oocytes at age 1 to 4,924 oocytes at age 4. Total fecundity (i.e., batch fecundity plus standing stock of yolked oocytes) increased from 3,017 eggs and yolked oocytes in age‐1 fish to 15,522 eggs and yolked oocytes in age‐4 fish. Of note, batch fecundity ranged from 57% to 68% across the four age‐classes indicating that over half of the total fecundity occurs in the first spawn. Average percent fertilization of eggs (63–82%) was not detectably different across the four age‐classes, while average egg diameter (4.1–5.5 mm) increased as age increased. Fecundity increased across all four reproductive age‐classes of Rio Grande Silvery Minnow, with the larger portion of total fecundity occurring in the first spawn across all age‐classes. The timing of spawning with optimal conditions in the Rio Grande is critical for survival and ultimately recruitment into the wild fish population.

No quarter: Lack of refuge during flow intermittency results in catastrophic mortality of an imperiled minnow

“…Rio Grande silvery minnow were once widespread (Bestgen & Platania, 1991; Treviño‐Robinson, 1959) and are vagile (Archdeacon et al., 2018; Platania et al., 2020), and they have high fecundity relative to other small‐bodied minnows (Caldwell, Falco, Knight, Ulibarri, & Gould, 2019), traits generally found among species resilient to drought (Lennox et al., 2019). Historically, RGS minnow populations could have recolonised disturbed areas from refuges upstream or downstream.…”

Quantifying flow and nonflow management impacts on an endangered fish by integrating data, research, and expert opinion

“…$$$ \upalpha $$$ was given a normal prior with a mean of 675 and a standard deviation (SD) of 135 based on fecundity estimates, an assumed sex ratio of 0.5, and a larval survival rate of 0.75. Based on the average standard lengths of age‐1, age‐2+, and augmented RGSM and the relative fecundity at these different sizes (Caldwell et al, 2019), $$$ {\upbeta}_A $$$ was given a normal prior with a mean of 1 and SD of 0.1, and $$$ {\upbeta}_2 $$$ was given a normal prior with a mean of 2 and SD of 0.1. Different versions of the model were run until they had approximately converged based on visual inspection of the three chains and values of $$$ \hat{R}<1.1 $$$.…”

“…All parameters were given weakly informative priors apart from parameters related to reproduction, which were informed by a past laboratory study on RGSM reproduction and early life history. Specifically we used information from Caldwell et al (2019) to develop priors for $$$ \upalpha $$$, $$$ {\upbeta}_A $$$, and $$$ {\upbeta}_2 $$$. $$$ \upalpha $$$ was given a normal prior with a mean of 675 and a standard deviation (SD) of 135 based on fecundity estimates, an assumed sex ratio of 0.5, and a larval survival rate of 0.75.…”

“…Absolute abundance estimates would not have been possible without 4 years of direct abundance estimates (Dudley et al, 2012). The model was also informed by prior studies of reproduction (Caldwell et al, 2019), larval habitat (Gonzales et al, 2014;Valdez et al, 2019Valdez et al, , 2021, and fish rescue (Archdeacon, 2016;. To interpret monitoring data, we made parametric assumptions about how mesohabitat availability and preference scales with discharge (Figure 5a,b) and used both existing data (e.g., Dudley et al, 2021) and expert elicitation to fit these relationships.…”

Fish Rescue during Streamflow Intermittency May Not Be Effective for Conservation of Rio Grande Silvery Minnow

“…Fishes with this life-history strategy are typically small, short-lived, have high reproductive output, and maintain high demographic resilience [31]. Rio Grande silvery minnow have a relatively short lifespan, with few living > 2 years [32]; they reach maturity in the first year of life [33] and have relatively high fecundity for their body size [34]. Rio Grande silvery minnow spawn non-adhesive, neutrally buoyant ova directly into the water column [35], a mode of reproduction found in several other cyprinid species in the Great Plains of the western United States [36].…”