Gonad metabolomics and blood biochemical analysis reveal differences associated with testicular oocytes in wild largemouth bass (Micropterus salmoides).

Adverse reproductive effects associated with gonadal intersex among freshwater fish could hold considerable implications for population sustainability. Presence of testicular oocytes (TO) is the most common form of intersex and is widespread among centrarchids (sunfishes) of North America and other freshwater teleosts. Placing TO within the toxicological context of adverse outcome pathways (AOPs) to assess ecological risk is a priority for ecotoxicologists due to the association of TO with harmful chemical exposure and adverse reproductive effects in some cases. However, key event relationships between EDC exposure, incidence of TO, and apical outcomes have yet to be fully elucidated - in part due to a lack of knowledge of relationships between intersex gonad physiology and fish health. Understanding the physiological status of intersex fish is critical to assess ecological risk, understand mechanisms of induction, and to establish biomarkers of intersex in fish. In the present study, features of gonad metabolite profiles associated with TO in largemouth bass (LMB, Micropterus salmoides) from an impoundment in Georgia (USA) were determined using GC-MS-based metabolomics. Clinical blood biochemical screens were used to evaluate markers of fish health associated with TO. Results suggest that physiological changes in energy expenditure as well as relatively 'feminized' gonad lipid and protein metabolism may be related to the occurrence of TO in male LMB, and highlight the need to understand relationships between intersex and physical stressors such as elevated temperature and hypoxia. These results provide novel insight to AOPs associated with TO and identify candidate analytes for biomarker discovery.

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

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 (r2 = 0.81) and severity reported by enumeration of testicular oocytes was moderately correlated across sites (r2 = 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.