Evaluation of the effects of retinoids and carotenoids on egg quality using a microinjection system

Preparation of high quality eggs is essential in aquaculture. While egg quality is widely regarded as being largely dependent on the nutrients that are stored in the yolk, the identity of the factors responsible for affecting this egg quality is not yet known. Thus, in order to ensure the quality of better quality eggs, it is essential to elucidate how the nutrients in yolk influence embryogenesis. Using a microinjection system, we performed two tests with zebrafish embryos to evaluate the effects of nutrients on embryogenesis. To determine whether retinoic acid, excess retinoids and carotenoids in yolk cause malformations, we injected retinoic acid, retinal, retinol and β-carotene into the yolk of 1–4 cell cell-stage embryos, and compared their effects on embryogenesis. The injection of retinal into yolk causes similar anomalies to those induced by retinoic acid in the brain, jaw, heart, as well as suppressing hatching rate. Retinol had a lower tetragenic effect than retinal and toxicity was not detected for β-carotene. These findings suggest that excess retinal and retinol in yolk can impair egg quality by causing malformations and decreasing hatching rate. We then compared the protective effects of astaxanthin, β-carotene and α-tocopherol against oxidative stress in embryos. After injecting one of these compounds into the yolk of a 1–4 cell-stage embryo, embryos were exposed to H2O2 for 2 h from 24 h post-fertilization (hpf) and mortality and apoptosis were observed at 48 hpf. Astaxanthin conferred embryos with a marked tolerance against mortality and apoptosis due to H2O2 exposure, suggesting its potential application to the improvement of egg quality by increasing the tolerance of embryos toward oxidative stress. The methodology presented herein describes a quick method for evaluating the effects of nutrients on egg quality.