Embryogenesis and early larval development of the fish Pimelodus grosskopfii (Siluriformes: Pimelodidae)

Introduction: Despite its ecological importance, a detailed characterization of the embryonic and early larval development is lacking for the neotropical siluriform Pimelodus grosskopfii. Objective: To describe the ontogenetic and larval development of P. grosskopfii. Methods: Key ontogenetic events were documented from fertilization through 20 days post-hatching using optical microscopy, histology, and scanning electron microscopy at 28.4 °C. Results: Embryonic development proceeded through six distinct stages (zygote, cleavage, blastula, gastrula, segmentation, and organogenesis) and was completed in 11.6 hours, notably faster than other neotropical siluriforms. Newly hatched larvae (4.6 ± 0.5 mm total length) develop from telolecithal eggs with meroblastic cleavage restricted to the animal pole. Histological analyses revealed accelerated organogenesis with barbel rudiments appearing by 13 hours post-hatching and specialized sensory corpuscles by 17.5 hours. The transition to endogenous feeding occurred at 17.5 hours post-hatching, with complete yolk sac absorption by 31 hours. By day nine, larvae developed multiple dental rows (30-40 teeth per row), and by day 14, histological sections revealed complete mandibular ossification and advanced development of olfactory rosettes, gill structures, and the digestive tract. Conclusion: This chronological sequence of morphological and histological changes provides a developmental framework for comparative studies among catfishes and contributes to understanding evolutionary patterns in teleost ontogeny.