ムスジカジ

Ernogrammus hexagrammus (Temminck et Schlegel) is a small blennioid fish, hiding under the stones lying in the tidal zone of rocky coasts, distributing from Hokkaido to Kyushu in Japan. The authors collected the egg masses of this fish at Manju Islet in Shimonoseki City on March 15, 1957, March 7, 1958 and February 24, 1959 and reared the hatched larvae for about 40 days in the glass jar feeding with brine shrimp nauplii. The spawning season seems to extend from January to March in the vicinity of Shimonoseki City. The eggs (Fig. 2, A) are sticking to each other to form a small spherical egg mass (about 30 mm in diameter), not adherent to any other substance. The spawned egg mass is laid under the stones lying near the low tide water mark, where it is guarded by a male parent fish. The individual egg (Fig. 2, B) is spherical, measuring 2.3-2.45 mm in diameter with a single oil-globule. The yolk and oil-globule are colorless. The egg membrane is almost opaque and pale milky white with a number of small wartlike structures on the surface. The developing eggs at 47-myotome stage, with hatching enzyme glands on the head of embryonal body, collected on March 7, 1958, were reared in the tank. The hatching took place in about 8 days after being collected at the water temperature 13-17.5℃. The newly hatched larvae (including the one of Fig. 2, C) are 8.75-9.25 mm in total length, with an oil globule situated at the middle part of the yolk and partly protruding from its surface. The myotome number is 15+30～32=45～47. The larvae fed actively on the brine shrimp nauplii in the day time, but in dark they did not feed at all. In four or five days the yolk was entirely consumed and the larva measured 9.65 mm (Fig. 2, D). For about twenty days after hatching the larvae lived a swimming life in the day time, settling down to the bottom of glass jar in the dark place or at night. In 23 days after hatching the rudiments of ventral fins were formed(Fig. 2, F). In 25-30 days after hatching, melanophores and orange pigment cells suddenly appeared almost all over the body, and the larvae (including the one of Fig. 2, G), now 12.7-13.0mm in total length, entered into the bottom life. These larvae scarcely fed on the brine shrimp nauplii. In 34 days after hatching the larvae (Fig. 2, H), 13mm in total length, reached early juvenile stage.