Sex assignment of lake sturgeon (Acipenser fluvescens) based on plasma sex hormone and vitellogenin levels

Abstract

This study focused on identifying the sex of lake sturgeon by measuring the sex hormones estradiol and testosterone, and the phosphoprotein vitellogenin (Vtg) in blood plasma by radioimmunoassay and enzyme-linked immunosorbent assay, respectively, and evaluating these techniques as tools in lake sturgeon population management. Surveys of the St Clair River (SCR) lake sturgeon population have characterized it as rebounding by having steady or increasing recruitment since 1997. However, researchers have not been able to effectively determine the sex for most of the sturgeon they capture because few fish caught during surveys are releasing gametes. A total of 115 fish were sampled from May through June in 2004 and 2005 from the SCR, Michigan, USA. Of these, only four females and eight males were verified (i.e. they were releasing gametes at time of capture), resulting in very few fish with which to validate blood hormone and Vtg biomarkers of sex. Fifty-six percent of the fish were assigned a sex designation based on biomarker criteria. Correspondence between actual gonadal sex and biomarker-directed classification was good for the small subset of fish for which gonadal sex was definitively determined. Moreover, application of the steroid values in a predictive sex assignment model developed for white sturgeon misclassified only the same two fish that were misclassified with the steroid and Vtg biomarkers. The experimental results suggest a sex ratio of 1 : 2.7 (F:M), however more conclusive methods are needed to confirm this ratio because so few fish were available for sex validation. Of the 43 males, 14 were within the legal slot limit, 11 were smaller than 1067 mm total length (TL), and 18 were larger than 1270 mm TL. All 15 females were larger than 1270 mm TL, and thus protected by the slot limit criteria. Considering that lake sturgeon are threatened in Michigan, an advantage to using blood plasma assays was that fish were not harmed, and sample collection was quick, simple, and inexpensive. However, because a sufficiently large number of fish could not be validated for gonadal sex due to handling restrictions given the fishÕs protected status, assignment of sex is not based on a robust multi-variate model. An immediate alternative may be to use other non-invasive field methods (e.g. ultrasound, fiber-optic endoscope) to provide a more timely classification while establishing well-validated plasma hormone and Vtg-based predictive models for sex assignment of lake sturgeon.

Using circulating reproductive hormones for sex determination of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in the Saco River estuary, Maine

“…In comparison to T concentrations in male maturing white sturgeon (150 ng ml −1 ), the mean SRE sturgeon value (49 ± 5.4 ng ml −1 ) was lower (Webb et al ., 2002). However, the adult male T mean in the SRE was higher than means in lake sturgeon (Craig et al ., 2009) and ‘the bester’ [F 1 hybrid beluga and sterlet sturgeon ( Huso huso L. female ×  Acipenser ruthenus L. male); Amiri et al ., 1996a], where T peaked at 5.023 and 28 ng ml −1 , respectively in each species.…”

“…This trend also corresponds to findings in maturing female white sturgeon (Webb et al ., 2002), showing the utility of a sex-determining equation between species, as used in the present study. The mean E 2 concentration in the present study (3.7 ± 0.3 ng ml −1 ) fell within the range of female adult ‘the bester’ hybrid (2–4 ng ml −1 ; Amiri et al ., 1996b) and female lake sturgeon (0.025–9.536 ng ml −1 ; Craig et al ., 2009) but was lower than adult female Gulf sturgeon (mean, 9.97 ng ml −1 ; Heise et al ., 2009). Additionally, in the present study, the immature female E 2 mean was an intermediate value (2.9 ± 0.2 ng ml −1 ) between mature females and all male sturgeon.…”

“…Juvenile individuals would be expected to have lower basal levels of T and E 2 , and conversely, adults would have significantly higher levels (e.g. Webb et al ., 2002; Craig et al ., 2009; Petochi et al ., 2011). These high levels of T and E 2 in the SRE could be attributed to individuals that are considered late-stage juvenile by FL that were undergoing sexual maturation at the time of sampling.…”

“…The classification used in this study from Webb et al . (2002) has been successfully used in lake sturgeon ( Acipenser fulvescens ), showing the utility of these types of classification equations even across sturgeon species (Craig et al ., 2009; Shaw et al ., 2012; Thiem et al ., 2013). However, the model created herein needs further investigation with spawning populations, in which mean hormone concentrations are generally higher than the mean values of T and E 2 in the SRE (Van Eenennaam e t al.…”

“…For example, T is an important androgen contributing to maturation in males and females (Cuisset et al ., 1995; Moberg et al ., 1995; Van Eenennaam et al ., 1996; Amiri et al ., 1996a, b; Webb et al ., 2002), whereas E 2 has been shown to increase during vitellogenesis and decrease during the terminal stages of oocyte maturation in females (Amiri et al ., 1996b; Doroshov et al ., 1997; Webb et al ., 2002). Thus, by using a ratio of T and E 2 concentrations, the sex of sturgeon can be determined (Craig et al ., 2009). For example, significant differences in androgen and E 2 concentrations were observed between sex and reproductive phases (i.e.…”