Morphology and chronology of critical events for early‐life history survival of an old word killifish, <i>Esmaeilius shirini</i> (Teleostei: Aphaniidae): A conservation management approach

Abstract In this study, the live cell imaging microscopy of an old word cyprinodontiform fish, the Shirini toothcarp Esmaeilius shirini during its embryogenesis, is described and illustrated for the first time through the detailed morphological description and chronology of the events of all developmental stages (from fertilization to hatching). External fertilization of transparent, spherical, sticky and macrolecithal eggs bearing adhesive filaments with an average diameter of 0.83–1 mm is the first step in the ontogenesis of E. shirini . Embryogenesis continued with a process of meroblastic cleavage (approximately 2 and half h post‐fertilization, hpf), formation of blastula (blastulation), gastrula (gastrulation), neurulation, somatogenesis, organ formation (organogenesis) and pre‐hatching. The development continued with hatching (a stage between the embryonic and larval periods) at approximately 131 haf (at 24 ± 1°C). The new larvae were about 3.9–5.8 mm in length with distinct fin rays and pigmentation on the head, body and fins. Basic data from this study can be used in forthcoming investigations on the reproduction processes, breeding, behaviour and conservation of E. shirini . Fish development comprises an integrated, ordered and well‐mapped sequence of early life‐history events controlled by intrinsic and extrinsic factors. Knowledge of fish developmental stages during embryogenesis/ontogeny is essential for a better understanding of their biology, breeding criteria, phylogenetic relationships, dietary requirements, conservation plans, environmental requirements and ecological preferences.