Differences in sexual development in inbred and outbred zebrafish (Danio rerio) and implications for chemical testing

• Published in: Aquatic toxicology Vol. 112-113; pp. 27 - 38
• Main Authors: Brown, A. Ross, Bickley, Lisa K., Ryan, Thomas A., Paull, Gregory C., Hamilton, Patrick B., Owen, Stewart F., Sharpe, Alan D., Tyler, Charles R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.05.2012; Elsevier
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Body Size; Breeding; Danio rerio; ecotoxicology; Ecotoxicology, biological effects of pollution; eggs; Female; females; fish; Fundamental and applied biological sciences. Psychology; General aspects; Genetic Variation; germ; Gonads - growth & development; hybrids; Inbreeding; karyotyping; laboratory animals; Male; Outbreeding; phenotype; Phenotypic plasticity; reproductive toxicology; sex ratio; Sexual development; Sexual Development - physiology; Species Specificity; Strain differences; Time Factors; Toxicity Tests; variance; viability; Zebrafish - genetics; Zebrafish - physiology; Phenotypic plasticity; Inbreeding; Sexual development; Strain differences; Outbreeding; Genetic variation; Genetic variability; Ecotoxicology; Toxicity; Mating system; Aquatic environment; Reproduction; Vertebrata; Brachydanio rerio; Pisces; Cyprinidae
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2012.01.017

► Under standard control conditions in a new Fish Sexual Development Test (FSDT) we compared a range of phenotypic endpoints in a WIK zebrafish strain and a WIK/Wild strain with three levels of inbreeding. ► Inbred WIK/Wild lines were male-biased and the WIK strain was female-biased beyond tolerance limits for sex ratio (30–70% females). ► Only the outbred line of WIK/Wild strain met all acceptance criteria stipulated for controls. ► Gonadal development was also more advanced in outbred WIK/Wild zebrafish compared to WIKs, offering greater scope to detect repro-toxicity. Outbred laboratory animal strains used in ecotoxicology are intended to represent wild populations. However, breeding history may vary considerably between strains, driving differences in genetic variation and phenotypes used for assessing effects of chemical exposure. We compared a range of phenotypic endpoints in zebrafish from four different “breeding treatments” comprising a Wild Indian Karyotype (WIK) zebrafish strain and a WIK/Wild strain with three levels of inbreeding (FIT=n, n+0.25, n+0.375) in a new Fish Sexual Development Test (FSDT). There were no differences between treatments in terms of egg viability, hatch success or fry survival. However, compared with WIKs, WIK/Wild hybrids were significantly larger in size, with more advanced gonadal (germ cell) development at the end of the test (63 days post fertilisation). Increasing the levels of inbreeding in the related WIK/Wild lines did not affect body size, but there was a significant male-bias (72%) in the most inbred line (FIT=n+0.375). Conversely, in the reference WIK strain there was a significant female-bias in the population (80% females). Overall, our results support the use of outbred zebrafish strains in the FSDT, where one of the core endpoints is sex ratio. Despite increased variance (and reduced statistical power) for some endpoints, WIK/Wild outbreds (FIT=n) met all acceptance criteria for controls in this test, whereas WIKs failed to comply with tolerance limits for sex ratio (30–70% females). Sexual development was also more advanced in WIK/Wild outbreds (cf. WIKs), providing greater scope for detection of developmental reproductive toxicity following chemical exposure.