Nonlethal laparoscopic detection of intersex (testicular oocytes) in largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieu)

Abstract

Intersex in wild fish populations has received considerable attention in the scientific literature and public media. Conventional detection of testicular oocytes, the presence of immature oocytes within testis of male fish, commonly employs transverse sectioning of excised testis and is lethal. The present study used a nonlethal laparoscopic technique to collect biopsies of testis from black bass, entering the body cavity via the genital pore. Detection of testicular oocytes was compared between biopsy and conventional methods using 79 smallmouth bass (Micropterus dolomieu) from 8 sites and 68 largemouth bass (Micropterus salmoides) from 4 sites. The 2 methods performed similarly at sites where testicular oocyte severity was moderate or high (6 of 8 smallmouth bass sites), whereas transverse sectioning resulted in superior testicular oocyte detection at sites where severity was low (2 of 8 smallmouth bass sites and all 4 largemouth bass sites). In smallmouth bass, testicular oocyte prevalence by transverse and biopsy methods was strongly correlated across sites (r = 0.81) and severity reported by enumeration of testicular oocytes was moderately correlated across sites (r = 0.59). Survival of a subset of largemouth bass (n = 20) to 28 d after laparoscopic surgery was 90%. The present research indicates that laparoscopy may be useful for monitoring the prevalence and severity of testicular oocytes in Micropterus species, particularly when lethal sampling is precluded. Environ Toxicol Chem 2017;36:1924-1933. © 2016 SETAC.

Testicular oocytes in smallmouth bass in northeastern Minnesota in relation to varying levels of human activity

“…Wild black bass populations ( Micropterus spp.) may also be subject to reproductive disruption, as evidenced by gonadal intersex rates as high as 100% of males per site in several major US river systems ; and according to a recent review, Micropterus dolomieu and Micropterus salmoides , combined, were the most commonly reported intersex fish species in North America . Intersex is considered abnormal in most gonochoristic fish , and is recognized as a potential biomarker of exposure to EDCs from anthropogenic sources .…”