Development of Labrus Bergylta (Ascanius 1767) Larvae from Hatching to Metamorphosis

Abstract

Ballan wrasse, Labrus bergylta (Ascanius, 1767), has commercial interest as a cleaner fish in aquaculture, and culture of juveniles may be a good alternative to catching wild fish. However, basic knowledge of early development is limited. To study hatching and larvae ontogenesis, eggs were collected from a broodstock of wild caught ballan wrasse held in captivity. Larvae were fed rotifers for 27 days; Artemia was introduced at day 20 and fed larvae to day 49 after hatching. Age at hatching, and larval ontogenesis based on external morphological features were linked to the chronological age of larvae as days post hatching (DPH) and physiological age as degree day (°C.day) and standard length (SL). The ballan wrasse egg diameter was 1.05 ± 0.04 mm and 0.87 ± 0.05 mm with and without the gelatinous layer, respectively, and hatched at a SL of 3.64 ± 0.05 mm, 7 days, i.e., 72°C.day, after fertilization. The ontogeny of larvae from hatching to metamorphosis was divided into four stages. Yolk sac larva, 0 to 9 DPH (SL 4.28 ± 0.11 mm), where mouth opens and pigmentation of the eyes is seen. Dilated swim bladder is visible. Preflexion larva, 10 to 25 DPH (SL 5.35 ± 0.30 mm); yolk sac has disappeared, and initial formation of caudal fin rays occurs. Gaseous inflation of swim bladder is observed. Flexion larva, 26 to 33 DPH (SL 5.9 ± 0.78 mm), initial resorption of primordial fin fold is seen. Postflexion larva, 34 to 49 DPH (SL 10.52 ± 0.82 mm) by the end of this stage (age 686°C.day), the dorsal, anal, caudal and pelvic fins were developed. The ontogenetic development, linked to SL, chronological and physiological age, provides a baseline reference and makes it possible to compare developmental levels in future studies of ballan wrasse in culture and wild populations.