Larval and juvenile development of dusky grouper Epinephelus marginatus reared in mesocosms

Abstract

The larval development of the dusky grouper Epinephelus marginatus up to the benthic juvenile stage is described in detail to establish a reference for their larval identification. Development is described in terms of ontogenetic changes in morphology, growth, pigmentation, fin structure and skeletal structure. Larvae were reared in mesocosms at a mean temperature of 24.3 degrees C, salinity of 36.5, dissolved oxygen of 6.4 mg l(-1) and pH of 8.2. Newly hatched larvae had an estimated total length (L-T) of 2.3 mm. On the second day post hatching the yolk was almost fully absorbed with traces of the oil globule still present, the eyes were already pigmented and mouth and gut functional. At this stage the cranial skeletal elements for feeding and breathing (mouth and gills) and the pectoral-fin support were already present. About 50% of the observed larvae had food in their guts. Pigmentation was very characteristic, consisting of two large chromatophores visible on the edge of the primordial fin, close to the midpoint of the post-anal region of the body and over the midgut and hindgut and post-anal portion of the body. At 2.9 mm L-T the emergence of the second dorsal-fin spine, characteristic of the Epinephilinae, was clearly visible. The pre-flexion stage started in larva of 3.2 mm L-T. At 5.5 mm L-T the larvae possessed posterior preopercular angle spines, and the dorsal and pelvic spines presented serrated edges and were pigmented. The water surface-tension-related death of the yolk sac and pre-flexion larvae described in the rearing of several other grouper species did not occur during E. marginatus culture. Notochord flexion, with initial ossification of the caudal-fin supporting elements, started at 6.6 mm L-T. At this stage the major melanophores, preopercular, dorsal and pelvic spines and mandibular teeth were already present. Transformation of larvae into juveniles occurred when larvae averaged 13.8 mm L-T. Juveniles with a mean L-T of 20.1 mm started to settle and most of them were benthic with a mean L-T of 26.8 mm. (C) 2013 The Fisheries Society of the British Isles