Using Ultrasound to Determine the Sex and Maturity of Lake Sturgeon in the Field

Sex determination of fish species in the field is difficult to assess when sexual dimorphism and gametes are not apparent.  For threatened and endangered fish, unobtrusive techniques are needed when determining sex to minimize stress and the potential for mortality.  The current study evaluates the use of a portable ultrasound unit to determine sex of lake sturgeon in the field.  The sex and maturity of 25 female and 61 male lake sturgeon was determined by visually inspecting gametes through a small incision.  Six images (vent transverse, mid transverse, anterior transverse, vent frontal, mid frontal, and anterior frontal) were collected from each sturgeon using a SonoSite MicroMaxx ultrasound unit.  The average time spent collecting images was 3 minutes and ranged 2-5 minutes once comfortable with operating procedures.  Images were analyzed and sex and maturity was assigned and compared with the 86 sturgeon of known sex and maturity.  Preliminary analysis indicates F4 (black egg), F5 (spawning) female, and M2 (fully developed) male gametes can be accurately identified during the spring spawning season.  This work shows the utility of using an ultrasound unit in the field to determine sex of female and male lake sturgeon in later reproductive stages around the spawning season.