Development of Free and Canal Neuromasts with Special Reference to Sensory Polarity in Larvae of the Red Spotted Grouper, Epinephelus akaara.

SUZUKI Nobuhiro, KAYANO Yasuhisa, MITO Tuzumi

doi:10.11233/aquaculturesci1953.44.159

Morphological changes of free neuromasts in larvae of the red spotted grouper, Epinephelus akaara were described. A free neuromast was found on the epidermal free surface of the head region in newly hatched larvae (1.25-2.01 mm TL) and their number increased on both the head and trunk with larval growth. All free neuromasts contained sensory cells of opposing polarity. The orientation of maximum sensitivity of free neuromasts, judged from the polarity of the sensory cells, coincided with the minor axis of the outline of the apical surface of the free neuromasts. Four-day-old larvae (2.36-2.47 mm TL) were at the postlarval stage and the polarity of head neuromasts at this stage was usually oriented along the antero-posterior axis of the fish, but occasionally had a dorso-ventral orientation. The apical surface of free neuromasts changed in outline from a circle to a lozenge as the number of sensory cells started to increase in the pelagic larval stage (twelve-day-old larvae, 5.54-7.71 mm TL) . Free neuromasts were oriented on lines tangential to concentric circles around the eyes and nostrils. The development of schooling was recognized concomitant with the formation of the canal organ in the head region in thirtyfive-day-old juveniles (18.15-18.91 mm TL) . Forty-five-day-old juveniles (5.54-7.71 mm TL) attained a benthic-life stage and had nearly mature canal organs. The cupulae of the free neuromasts changed from a stick-like to a blade-like shape on both the head and trunk.

Development of Free and Canal Neuromasts with Special Reference to Sensory Polarity in Larvae of the Red Spotted Grouper, Epinephelus akaara.

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