Geology topics

Jason G. McLellan

Publications and source records attributed to Jason G. McLellan.

3 recordsLinked to original sources

USGS2022

Nonlethal tools to identify mass ovarian follicular atresia in Burbot

Skipped spawning, or variation in spawning periodicity, occurs in many annual spawning fish species and is an important consideration for population management. We assessed plasma sex steroid concentrations and measured gonad size and ovarian follicle diameter as metrics to nonlethally identify mass ovarian follicular atresia, which may contribute to skipped spawning in Burbot Lota lota . We maintained wild fish in captivity and exposed them to increasing water temperatures during a 3-wk period before the spawning season to induce mass ovarian follicular atresia. We collected ovarian follicles, blood plasma, and gonadal sonograms from fish weekly between January 28, 2018, and March 25, 2018. We histologically analyzed ovarian follicles to confirm stage of maturity. We measured concentrations of plasma sex steroids testosterone (T) and estradiol-17β (E2) by radioimmunoassay. We measured gonad diameter and circumference by ultrasonography and ovarian follicle diameter by image analysis. Mean plasma T concentration decreased from 8.94 ng/mL during late vitellogenesis to 1.83 ng/mL during atresia, suggesting that plasma T concentrations may be used to identify mass ovarian follicular atresia. We do not recommend using plasma E2 concentrations to identify mass ovarian follicular atresia because E2 concentrations rapidly decreased during the completion of vitellogenesis and the initiation of atresia in Burbot; therefore, plasma E2 may not accurately identify mass ovarian follicular atresia. Mean gonad diameter measured by ultrasonography decreased from 4.05 cm during late vitellogenesis to 3.65 cm during atresia. Mean diameter of ovarian follicles decreased during the final week of the study, suggesting that ovarian follicle diameter may be used to identify advanced mass ovarian follicular atresia. The nonlethal tools assessed—plasma sex steroid concentrations, ultrasonography, and ovarian follicle diameter—enable fisheries biologists to determine the occurrence and frequency of mass ovarian follicular atresia among Burbot in Lake Roosevelt and may be applied to other Burbot populations.

Journal of Fish and Wildlife Management↗

USGS2021

Gonad size measured by ultrasound to assign stage of maturity in Burbot

We measured gonad size (diameter and circumference) by ultrasound and used it as a metric to assign stage of maturity in Burbot Lota lota from Lake Roosevelt, Washington. We collected paired gonad tissue and ultrasound measurements monthly from November 2017 to March 2018 and processed gonad tissue for histological analysis to confirm stage of maturity. We measured gonad diameter and circumference by ultrasound. We also measured excised gonad diameter (i.e., true gonad diameter) by digital calipers and excised gonad circumference (i.e., true gonad circumference) by a measuring tape. All late vitellogenic (stage 6) ovaries measured by ultrasound had a diameter greater than 3.90 cm, suggesting a value of 3.90 cm or greater may be used to characterize females capable of spawning in the current reproductive cycle. One mid-spermatogenic (stage 3) and all ripe (stage 4) testes were too large to be measured and were assigned a diameter of 5.11 cm, the maximum value capable of being measured by our ultrasound transducer. A value of 5.11 cm or greater may be used to characterize males capable of spawning in the current reproductive cycle. Testis circumference measured by ultrasound is not reported because some testes were wider than the ultrasound transducer and could not be measured. Measurements of testis diameter did not differ between measurement methods (ultrasound versus true), but ultrasound measurements of ovary diameter and circumference were higher than true measurements. We attributed the difference between measurement methods to flattening of the ovary while applying the ultrasound transducer. Gonad diameter and circumference measured by ultrasound were highly correlated with gonadosomatic index and ovarian follicle diameter, indicating gonad size measured by ultrasound is an appropriate index of gonad development in Burbot.

Washington↗

USGS2020

Gametogenesis and assessment of nonlethal tools to assign sex and reproductive condition in Burbot

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.

Washington↗