Evaluation of scale development and its regeneration potency in the desert killifish under laboratory conditions

Scale development and its regeneration potency were evaluated in a desert killifish Aphaniops hormuzensis (family Aphaniidae) in laboratory conditions by using light and scanning electron microscopy. Scale development in A. hormuzensis took 156 days at room temperature. Four specific regions of scale formation were detected. The first scale development began 13 days post-hatching (dph) (total length [TL] = 8.5 mm) at the caudal peduncle region and is extended anteriorly 26 dph (TL = 13.6 mm) at the area below the dorsal fin. Scales began forming independently in the head region at 33 dph (TL = 21.7 mm), and in the abdominal region, began at 41 dph (TL = 25.8 mm). Additional points of scale origin were detected on the sides of the operculum or behind and below the eyes. Scale regeneration in the caudal peduncle started 6 days after removal (dar). In 16 dar, the microstructural features appeared and the growth circles, a wide and oblong focus (focus length = 0.6 ± 0.05 µm), and lepidonts were also formed. In 36 dar, the scale shape was gradually changed from circular to a polygon, and radii were distinguishable in the anterior field. The pattern of scale formation could be useful in enhancing the understanding of systematics and phylogeny, functional morphology, and habitat use. It could also be useful in helping to define the Larval/juvenile transition period.