The effect of different kinds of electrolyte and non-electrolyte solutions on the survival rate and morphology of zebrafish Danio rerio embryos

Optimization of vitrification factors for embryo cryopreservation of kelp grouper (Epinephelus moara)

Cryopreservation of marine fish embryos causes to severe cryogenic damage, and to date, adults have not been reared from embryos that were cryopreserved. Here, we optimized vitrification factors to improve the survival and hatching rate of kelp grouper (Epinephelus moara) embryos after cryopreservation. We screened the effects of 11 vitrification solution concentrations (25-50%) on the survival rate of embryos at four developmental stages (16S, 18S, 22S, TB). We investigated the effects of different equilibration time (25-45min) on the survival rate and the influence of vitrification solutions on embryonic volume. In addition, we tested the effects of treating embryos at five different developmental stages (4-6S, 16S, 22S, TB, HB) with different vitrification solutions (35% PMG3S and 35% PMG3T), prechilling temperature (-5 °C and 4 °C) and prechilling time. In total, 9855 embryos were cryopreserved at 10 developmental stages, from optic capsule stage to pre-hatch stage. We found that kelp grouper embryos performed best at equilibration time of 30 min. Embryos at the tail-bud stage exhibited greater tolerance to vitrification than other stages. Vitrification solutions that contained sucrose showed better survival rates compared to embryos treated with vitrification solutions containing trehalose. Pre-chilling treatment improved viability before freezing, but did not improve viability after freezing. In the most optimal condition we identified in this study, the average survival, normal development and malformation rates of cryopreserved embryos were 6.32%, 2.36% and 3.49%, and 39.85% of the surviving embryos that were cryopreserved hatched. The hatched larvae gradually died at day 12 of cultivation, where the longest surviving individuals lived for 16 days. This study provides valuable data for improving survival and hatching rate of cryopreserved grouper embryos, and provides references for further exploring techniques in fish embryo cryopreservation.

Transcriptional changes in Atlantic salmon (Salmo salar) after embryonic exposure to road salt

Road salt is extensively used as a deicing chemical in road maintenance during winter and has in certain areas of the world led to density stratifications in lakes and ponds, and adversely impacted aquatic organisms in the recipients of the road run-off. Aquatic vertebrates such as fish have been particularly sensitive during fertilisation, as the fertilisation of eggs involves rapid uptake of the surrounding water, reduction in egg swelling and in ovo exposure to high road salt concentrations. The present study aimed to identify the persistent molecular changes occurring in Atlantic salmon (Salmo salar) eggs after 24h exposure to high concentrations (5000 mg/L) of road salt at fertilisation. The global transcriptional changes were monitored by a 60k salmonid microarray at the eyed egg stage (cleavage stage, 255 degree days after fertilisation) and identified a high number of transcripts being differentially regulated. Functional enrichment, pathway and gene-gene interaction analysis identified that the differentially expressed genes (DEGs) were mainly associated with toxiciologically relevant processes involved in osmoregulation, ionregulation, oxidative stress, metabolism (energy turnover), renal function and developmental in the embryos. Quantitative rtPCR analysis of selected biomarkers, identified by global transcriptomics, were monitored in the eggs for an extended range of road salt concentrations (0, 50, 100, 500 and 5000 mg/L) and revealed a positive concentration-dependent increase in cypa14, a gene involved in lipid turnover and renal function, and nav1, a gene involved in neuraxonal development. Biomarkers for osmoregulatory responses such as atp1a2, the gene encoding the main sodium/potassium ATP-fueled transporter for chloride ions, and txdc9, a gene involved in regulation of cell redox homeostasis (oxidative stress), displayed apparent concentration-dependency with exposure, although large variance in the control group precluded robust statistical discrimination between the groups. A No Transcriptional Effect Level (NOTEL) of 50mg/L road salt was found to be several orders of magnitude lower than the adverse effects documented in developing fish embryos elsewhere, albeit at concentrations realistic in lotic systems receiving run-off from road salt. It remains to be determined whether these transcriptional changes may cause adverse effects in fish at ecologically relevant exposure concentrations of road salt.