Abstract
Simple SummaryThe maintenance and manipulation of AB strain zebrafish oocytes at 26 °C was found to be possible for 2 h without incurring a marked reduction in fertilization potential. However, the post-ovulatory ageing of oocytes for 6 h resulted in an almost complete loss of egg viability. All larvae derived from the 4- and 6-h aged oocytes were characterized by physical abnormalities. Ageing oocytes for 4 h resulted in the incidence of ploidy anomalies having a four-fold increase. These results make a valuable contribution with respect to the control of experimental reproduction in zebrafish, which is currently accepted as an excellent model animal.Fish egg quality can be markedly influenced by the oocyte age after ovulation. In this study, we examined the duration of oocyte ageing in the zebrafish (Danio rerio) and whether prolonged ageing is associated with the incidence of ploidy anomalies in the resulting embryos. Oocytes were incubated in vitro for 6 h post-stripping (HPS) at 26 °C and fertilized at 2-h intervals. Meanwhile, for eggs fertilized immediately after stripping, the fertilization, embryo survival, and hatching rates started at ~80%; these rates decreased to 39%, 24%, and 16%, respectively, for oocytes that had been stored for 4 h (p ˂ 0.05), and there was an almost complete loss of egg viability at 6 HPS. Furthermore, almost 90% of the embryos derived from 6-h aged oocytes died prior to hatching, and all larvae originating from 4- and 6-h aged oocytes showed malformations. The proportion of ploidy abnormal embryos was significantly greater at 4 HPS (18.5%) than at either 0 or 2 HPS (4.7% and 8.8%, respectively). The results revealed that zebrafish oocytes retained their fertilization potential for up to 2 h after stripping at 26 °C and indicated the contribution of post-ovulatory oocyte ageing in the occurrence of ploidy anomalies in the resulting embryos.
Highlights
We examined the rates of fertilization, embryo survival, hatching, embryo mortality, and larval malformation for eggs originating from oocytes of different ages
Only 5% of the control group (0 h post-stripping (HPS)) larvae showed any evidence of malformation; all the larvae originating from 4- and 6-h aged oocytes were observed to be malformed, mostly suffering from the skeletal abnormalities
The developmental competence of fish embryos is critically dependent on the integrity of oocytes, and our examination of the effects of zebrafish oocyte ageing on embryo survival and hatching rates in the present study revealed that the corresponding rates were significantly lower in the eggs derived from oocytes aged for 2, 4, and 6 h than those derived from fertilized fresh oocytes
Summary
The gametes of female organisms, are the final products of oogenesis, during which all essential components, such as maternal mRNAs, proteins, lipids, carbohydrates, vitamins, and hormones, that support initial embryonic development are incorporated [1]. These maternally incorporated endogenous factors are important for ensuring the production of good-quality eggs, and they subsequently contribute to successful fertilization and successful embryo development [2,3]. Oocyte ageing appears to be a complex process involving multiple pathways. The precise pathways underlying oocyte ageing have yet to be sufficiently characterized
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