3.2.1. Yolk resorption
During endotrophic phase (stage 1) which in tuna includes the
larvae during the first two days after hatching (0–1 dph), the mouth
and the anus were still closed. At hatching, the larvae presented an
acidophilic yolk-sac surrounded by the periblast or yolk syncytial layer
of squamous epithelium. The yolk-sac showed an acidophilic homogeneousmatrix
or yolkmass containing an evident single-large oil globule
composed by neutral lipids and both yolk-structures surrounded by the
periblast (Fig. 4a, b and c). At 1 dph, evident signs of yolk fragmentation
and granular yolk appearance were detected, as a consequence of the
yolk resorption process during the two first days after hatching. During
stage 2 or endo–exotrophic phase, around 2–3 dph, the remaining yolk
matrix was observed with a reduced periblast and connected to the
developing liver. The yolk-sac was not perceptible from 4 dph.