Abstract
Morphology and physiology of fish embryos undergo dramatic changes during their development until the onset of feeding, supplied only by endogenous yolk reserves. For obtaining an insight how these restructuring processes are reflected by body mass related parameters, dry weights (dw), contents of the elements carbon and nitrogen and lipid and protein levels were quantified in different stages within the first four days of embryo development of the zebrafish (Danio rerio). The data show age dependent changes in tissue composition. Dry weights decreased significantly from 79μgdw/egg at 0hours post fertilization (hpf) to 61 μgdw/egg after 96 hpf. The amounts of total carbon fluctuated between 460 mg g-1 and 540 mg g-1 dw, nitrogen was at about 100 mg g-1 dw and total fatty acids were between 48–73 mg g-1 dw. In contrast to these parameters that remained relatively constant, the protein content, which was 240 mg g-1 at 0 hpf, showed an overall increase of about 40%. Comparisons of intact eggs and dechorionated embryos at stages prior to hatching (24, 30, 48 hpf) showed that the differences seen for dry weight and for carbon and nitrogen contents became smaller at more advanced stages, consistent with transition of material from the chorion to embryo tissue. Further, we determined the effect of 2,4-dinitrophenol at a subacutely toxic concentration (14 μM, LC10) as a model chemical challenge on the examined body mass related parameters. The compound caused significant decreases in phospholipid and glycolipid fatty acid contents along with a decrease in the phospholipid fatty acid unsaturation index. No major changes were observed for the other examined parameters. Lipidomic studies as performed here may thus be useful for determining subacute effects of lipophilic organic compounds on lipid metabolism and on cellular membranes of zebrafish embryos.
Highlights
The development of embryos involves a continuous, fundamental restructuring of the embryonic organism
Considering that growth of the fish embryo proceeds without uptake of external resources and entirely relies on endogenous supplies, we address the question how the restructuring process during development is reflected by changes in body mass related parameters
As detailed further below, there is evidence that constituents of the chorion become available as physiologically relevant resources to the embryo within the chorion and that the contribution of the chorion to dry weight, carbon and nitrogen content decreases over time
Summary
The development of embryos involves a continuous, fundamental restructuring of the embryonic organism. More advanced fish life stages maintain comparatively high levels of exchange between internal compartments and the exterior via specific organs (gills and intestines) with large surface areas at the organism—environment interfaces for gas and ion exchange and the uptake of nutrients [1]. Regarding their morphology and physiology, early developmental and adult stages of fish substantially differ. This suggests that those stages may be differently affected and differently sensitive to toxic agents. In contrast to further advanced stages, experiments with fish eggs and eleutheroembryos are not regarded as animal experiments in many countries and they are promoted as an alternative ecotoxicological experimental fish model [4]
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