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

Abstract

Gonad size (diameter and circumference) measured by ultrasound was assessed as a metric to assign stage of maturity in Burbot Lota lota from Lake Roosevelt, Washington. Paired gonad tissue and ultrasound measurements were collected monthly from November 2017 to March 2018. Gonad tissue was processed for histological analysis to confirm stage of maturity. Gonad diameter and circumference were measured by ultrasound. Excised gonad diameter (i.e., true gonad diameter) was measured by digital calipers, and excised gonad circumference (i.e., true gonad circumference) was measured 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 assigned 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 vs. true), but ultrasound measurements of ovary diameter and circumference were higher than true measurements. We attributed the difference between measurement methods to flattening of 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.

Population Reproductive Structure of Rainbow Trout Determined by Histology and Advancing Methods to Assign Sex and Assess Spawning Capability

“…For males in this study, there were many larger fish that had extremely small gonad lobes (low GSI; 8% of ≥300‐mm males), which is unusual and contributed to lower accuracy. Testicular size measured by ultrasonography has been found to be highly correlated with GSI and reproductive condition (i.e., spawning capability) in Burbot Lota lota (McGarvey et al 2021) and should be further examined in Rainbow Trout. Applying size‐based criteria in the field to determine when to use ultrasonography (e.g., lower limit of ≥300 mm) will provide much more robust estimates of the proportion of spawning capable fish relative to gamete expression, and ultrasonography does not require sacrificing the fish.…”

Are the Coastal Waters of French Guiana a Source or Sink Habitat for Atlantic Goliath Grouper Epinephelus itajara?

“…To better understand the life cycle of Goliath Grouper in French Guiana and their connectivity with other populations, further research is recommended. This could include the determination of sex and maturity stage of live fish using ultrasound, which has emerged in recent years as an appropriate tool (e.g., [65], so as to identify potential prespawners and post-spawners. Additionally, tracking and telemetry studies across multiple locations in French Guiana and the Caribbean would help determine whether mature fish migrate from French Guiana to spawn and whether they return post-spawning.…”