Organogenesis of Ballan Wrasse Labrus Bergylta (Ascanius 1767) Larvae

Abstract

The organogenesis of ballan wrasse, Labrus bergylta, Ascanius, 1767 larvae was studied during the first 49 days after hatching (DAH) with histological and histochemical methods. During the yolk sac stage (0-9 DAH), a syncytial layer had surrounded the yolk sac. At mouth opening, we distinguished a primordial liver and swim bladder, a buccopharyngeal cavity with gill arch cartilages, an exocrine and endocrine pancreas, and a primordial gastrointestinal tract. By the end of this stage, the heart had become functional, the swim bladder had dilated, olfactory organs and inner ear otoliths had developed, the pituitary gland and thyroid follicle could be distinguished, and the eye had become pigmented. During preflexion (10-25 DAH), the swim bladder had inflated, and the renal corpuscles and tubules had joined the collecting duct towards the urinary bladder. Mucous cells were observed, which may provide secretions that protect against abrasion and pathogens. The density of these cells increased in the buccopharyngeal cavity and oesophagus. During flexion (26-33 DAH), secondary lamellae had developed. Increasing functionality of the digestive system coincided with a shift to the appearance of AB-positive mucous cells in the gill openings and the digestive tract. In addition, pharyngeal teeth had developed, which suggested that food preferences might change to include hard-bodied prey. Stage 4 was mainly characterized by increases in the size and complexity of pre existing organs and structures. At 49 DAH, metamorphosis was complete. The temporal sequence of development of the various systems may provide baseline information for aqua culturists and fish biologists in future studies on fish health, feed, feed development, and cultivation of ballan wrasse.