Fig. 2

Early embryonic development of A. burtoni. a On the day of fertilization (0 dpf) embryos develop until gastrulation – (shown is a blastula stage embryo, ~ stage 5). As in other teleosts, embryos develop on top of the yolk. b, c At 1 dpf, the neural tube and a head Anlage have formed (stage 10 shown). d, e By 2 dpf (stage 14), the embryos have developed pigmentation on the yolk, and a clear head can be distinguished, with presence of the mid-hindbrain boundary, otic vesicles and unpigmented eyes. At this stage, embryos are still surrounded by their chorion and the embryo shown has been manually dechorionated. f, g By 3 dpf (stage 15), the anterior-posterior axis has elongated further, pectoral fin Anlagen have appeared, and a clearly beating heart is visible. The eyes have developed light pigmentation. Also at this stage, embryos are still surrounded by their chorion, and the embryo shown has been manually dechorionated. h, i By 4 dpf (stage 17), the head has lifted up from the yolk, strong blood circulation through the heart is visible, and extensive vasculature runs across the yolk. All stages are indicated following the staging table for Nile tilapia [41]. Abbreviations: dpf: days post fertilization; st.: stage; BD: blastodisc; NT: neural tube; MHB: mid-hindbrain boundary; E: eye; OV: otic vesicle; PF: pectoral fin; H: heart; HA: Head Anlage