Development of sense organs in the Japanese sardine Sardinops melanostictus

Abstract

The developmental processes of the olfactory organ, taste buds, lateral line system, and inner ear in the Japanese sardine Sardinops melanostictus were examined in reared and wild specimens. Both the ciliated and microvillous receptor cells in the olfactory organ were found shortly after hatching. Formation of the olfactory nostrils and lamellae began at about 20 mm standard length (SL). The calculated inflection points in the relationship between the number of olfactory lamellae and standard length were at 30.3 and 62.7 mm SL. Taste buds first appeared in a 16.1-day-old larva of 11.2 mm notochord length. Newly hatched larvae were equipped with 12 pairs of neuromasts on the head and trunk. The formation of the lateral line canal commenced at about 20 mm SL and the four canals had ossified by 32.5 mm SL. At hatching, the inner ear was an oval-shaped auditory vesicle with two otoliths. Three semicircular canals formed by the first-feeding stage, and larvae assumed an upright position. The pro-otic bulla was gas-filled and formation of the lagena pocket began at about 20 mm SL. The saccular sac was entirely formed by about 32 mm SL. From the present results, the basic structure of the sense organs was almost completed by 32 mm SL, and the adult condition might be attained at 60-70 mm SL, as suggested by the second inflection point in the relationship between the number of olfactory lamellae and SL.