Yuguo Xia

Cytochrome P450 (Cyp)17A1 has both 17a-hydroxylase and 17,20-lyase activities, which are involved in the steroidogenic pathway that produces androgens and estrogens. Previously, a phenotype of all-male cyp17a1-deficient zebrafish generated by transcription activatorlike effector nuclease has been reported. In the current study, the mechanisms relating to Cyp17a1 that are involved in the development of sexual traits, especially gonadal differentiation and testicular development, were characterized. We found that the cyp17a1-deficient fish at 3 months postfertilization (mpf) were all fertile males with normal testis and spermatogenesis but compromised male-typical mating behaviors and secondary sex characters (SSCs), including breeding tubercles, body pigmentation, and anal fin coloration. These results demonstrate that spermatogenesis and testicular development are not as susceptible to androgen deficiency compared with the formation of male-typical SSCs and mating behaviors in zebrafish. The differentiation of the juvenile ovary into the mature ovary failed during the critical sexual differentiation stage. This all-male phenotype of the cyp17a1-deficient fish could be restored with testosterone or estradiol treatment. For testicular development in cyp17a1deficient fish, a gradually increasing number of spermatozoa and testis hypertrophy from 3 to 6 mpf were observed, accompanied by constitutively upregulated pituitary gonadotropin FSH subunit b (fshb). The hypertrophic testis and enhanced spermatogenesis in the cyp17a1-deficient fish at 6 mpf could be effectively rescued by fshb depletion. These results confirm that adequate estrogen is essential for maintaining ovarian differentiation, and they provide new insight into the role of FSHb in male testicular development and spermatogenesis. (Endocrinology 159: 3549-3562, 2018) M ating success and fecundity result from proper coordination of the development and expression of various sexual traits, including reproductive organs, mating behaviors, and secondary sex characters (SSCs). It is well established that sex steroid hormones exert considerable influence on the formation of these sexual traits in both mammals and fish (1-8). Recently, zebrafish have emerged as a well-developed model for the reproductive research of the steroidogenic pathway (see below), as zebrafish possess several advantages, including the ease of fertility evaluation and gonadal dissection, observability of germ cells in vivo, and, in particular, the successfully adopted knockout strategy (7, 9-13). In the current study, sexual traits were deeply characterized from the cytochrome P450 (cyp) 17A1 (cyp17a1)-deficient zebrafish, a model that has defective synthesis of androgens (6).

Abstract Individual specialization and high plasticity in feeding activity are common in natural populations. However, the role of these two in intraspecific competition is unclear. In this study, the rhythm of feeding activity, dietary composition, niche width, niche overlap, and individual specialization was explored in four different size groups of black amur bream ( Megalobrama terminalis ), using microscopic identification of foregut contents and stable isotope analysis ( δ 13 C and δ 15 N) of dorsal muscle. Both methods observed ontogenetic shifts in dietary preference and individual specializations, and revealed that the total niche width of large individuals was greater than small individuals. Mixed linear models indicated that feeding activity was significantly influenced by time ( p < 0.0001), and no significant changes among size groups was evident ( p = 0.244). Niche overlaps revealed that there was intensive diet competition between different size groups of black amur bream. Individual specialization in small juveniles was likely to be stronger than sub-adult and adult groups. Pearson’s correlation analysis revealed that the individual specialization was positively correlated with mean diet similarity within a group. The results indicated that intraspecific competition is reduced mainly by individual dietary specialization, rather than shift in feeding activity.

Abstract Cultivation of the redtail culter Culter mongolicus has been increasing substantially over the last decade along the Yangtze River basin; such increases in production lead to increased juvenile transportation. However, redtail culter juveniles have high transport mortality rates due to a strong stress response that is exacerbated by the accumulation of toxic metabolic waste. Through a 24-h simulated transport experiment (sampling every 6 h), we assessed effects of tricaine methanesulfonate (MS-222) at 10 mg/L of water, 20 mg/L, and 40 mg/L on redtail culter survival and water quality parameters, and similarly we assessed clove oil at 2 mg/L of water, 5 mg/L, and 10 mg/L. None of the anesthetics significantly improved water quality during the initial 6–12 h of the experiment. However, MS-222 treatments at the first 12–24 h of the experiment had significantly higher dissolved oxygen (DO), ammonia, and pH than the control but failed to decrease un-ionized ammonia content. In contrast, the clove oil treatment significantly reduced the un-ionized ammonia but failed to improve DO and pH at 12–24 h. The improvements in water quality were reflected in cumulative mortality, MS-222 and clove oil anesthetic treatments having significantly lower cumulative mortality than the control at 12–24 h. The MS-222 and clove oil slowed water quality deterioration, ensured a better transport environment, and improved juvenile survival during transportation. We recommend 5 mg/L clove oil be used when transporting juvenile redtail culters because that concentration improves fish survival while keeping cost low.