Gametogenesis and Assessment of Nonlethal Tools to Assign Sex and Reproductive Condition in Burbot

Abstract

Nonlethal tools (plasma sex steroid concentrations and ultrasound) for assigning sex and reproductive condition in Burbot Lota lota from Lake Roosevelt, Washington, were assessed. Gonadal tissue, blood plasma, and gonadal sonograms were collected monthly from November 2016 to March 2018. Gametogenesis was described by gonadal histology during an entire reproductive cycle to confirm sex and reproductive condition. Plasma testosterone (T) and estradiol‐17β (E2) concentrations were measured by radioimmunoassay. Plasma 11‐ketotestosterone (11‐KT) concentrations were measured by liquid chromatography–mass spectrometry. Plasma sex steroid profiles, gonadosomatic index, and ovarian follicle diameter were also described during an entire reproductive cycle. Plasma 11‐KT concentration was used to assign sex with 82% accuracy during the entire reproductive cycle, and plasma 11‐KT and E2 concentrations were used to assign sex with 98% accuracy when fish were reproductive (i.e., November–March in Lake Roosevelt). Plasma T and E2 concentrations were used to assign reproductive condition in females with 98% accuracy, and plasma T concentration was used to assign reproductive condition in males with 90% accuracy. Ultrasound was used to assign sex with 96% accuracy but was not useful for assigning reproductive condition. Nonlethal tools to assign sex and reproductive condition will enable fisheries biologists to assess reproductive indices of the Burbot population in Lake Roosevelt to inform management decisions.

Gonad Size Measured by Ultrasound to Assign Stage of Maturity in Burbot

“…Ultrasound can be used to assign sex (McGarvey et al 2020) and is a promising tool to assign stage of maturity in Burbot. Ultrasound is nonlethal and noninvasive, therefore eliminating the need to sacrifice fish and reducing stress experienced by fish compared with other indices of gonad development (e.g., gonad histology, GSI, ovarian follicle diameter, and plasma sex steroids; Blythe et al 1994).…”

“…We euthanized six fish by an overdose of MS-222 (500 ppm) monthly from November 2017 to March 2018 (seven fish were euthanized in January 2018) for biological sampling. We selected equal numbers of females and males using ultrasound (McGarvey et al 2020). We collected the following biological data from individual fish: total length (60.1 cm), body weight (60.01 g), gonad weight (60.01 g), ultrasound measurements of gonad diameter and circumference (60.01 cm), measurements of excised gonad diameter and circumference (60.01 cm; i.e., true gonad diameter and circumference), and gonad tissue (Data S1, Supplemental Material).…”

“…We then embedded tissue samples in paraffin wax, sectioned them at 5 lm, and stained sections with periodic acid-Schiff for histological analysis (Webb and Erickson 2007). We examined slides under a Leica DM compound microscope (250-4503; Leica Biosystems Inc., Lincolnshire, IL) and assigned a stage of maturity to germ cells in gonad tissue using our description of gametogenesis in Burbot (McGarvey et al 2020; Table 1).…”

“…Ultrasound has been used to nonlethally assign sex, stage of maturity, and reproductive condition in fishes by detecting morphological and echogenic differences among gonads (Shields et al 1993;Moghim et al 2002;Colombo et al 2004;Evans et al 2004;Novelo and Tiersch 2016). In a previous study, we assessed the use of ultrasound to assign sex, stage of maturity, and reproductive condition in adult Burbot Lota lota (McGarvey et al 2020). We used ultrasound to assign sex with 96% accuracy, but ultrasound could not be used to assign stage of maturity and reproductive condition by detecting morphological or echogenic differences among gonads.…”

“…The objective of this study was to assess gonad size (diameter and circumference) measured by ultrasound as a metric to assign stage of maturity in Burbot from Lake Roosevelt. Using ultrasound to assign sex (McGarvey et al 2020) and stage of maturity will enable fisheries biologists to nonlethally and noninvasively assess indices of reproductive potential (e.g., sex ratio, reproductive structure, and spawning periodicity) for the Burbot population in Lake Roosevelt.…”