The Life History of the Gobiid Fish, Expedio parvulus

Expedio parvulus SNYDER, a relative of Luciogobius guttatus GILL, growing to 50mm in full grown size, but lacking the ventral fin. The fish had been collected only from Misaki, Kanagawa Pref. and Onahama, Fukushima Pref. in Japan. The authors examined over one hundred specimens newly collected from Hayama in Kanagawa Pref., Tsuyazaki in Fukuoka Pref., Meshima Island and Nomozaki both in Nagasaki Pref. At the rocky shore of Akase, a small reef situated in the coast near the Fisheries Experimental Station of Nagasaki University in Nomozaki (Lat. 32° 35.3\u27N, Long. 129° 45.5\u27E), the fish was found concealing itself in sand and gravel sedimented under stones or pebbles laying the intertidal zone, and feeding on gammarus, copepods and larvae of shells. In May and August, 1971 three egg masses of this fish attaching to the under sides of stones and a piece of a roof tile laying in the habitat were collected. In two cases of the spawnings each egg mass was guared by a male parent staying under the stone or roof tile. The egg mass rather dense in one layer, and the eggs numbered 79 and 102 in the two cases. The eggs are club-shaped being 1.90 to 2.10mm in long axis and 0.62 to 0.68mm in short axis, and each provided with a shallow depression encircling at the distal end and a bundle of adhesive filaments at the basal end. The eggs are similar to those of Luciogobius guitatus in shape, but a little smaller than the latter. It took 144 to 168 hours for development from the formation of the embryonic shield to the hatching at the water temperature changing from 19.3℃ to 21.3℃. The newly hatched larva is 3.43mm in total length and it is provided with the large eyes, a remnant of yolk, 44 (23+21) myomeres, and the anus opening in the posterior part of the body. The melanophores and xanthophores in the dorsal mid line are characteristic in disposition. Fifty individuals of the newly hatched planktonic larvae were reared in a 30 liter plastic aquarium, and six of them grew up to the juveniles over 15mm in total length entered into the bottom life in 32 days. They were fed with trocophore larvae of the oyster, Crassostrea gigas in the first feeding stage and with the rotifer, Brachionus plicatilis, nauplii of brine shrimp, Artemia salina and planktonic copepods from sea in the next stage. Along with the larval development, the larva became more slender and cylindrical in body form, and the eyes and pectoral fins relatively reduced in size. The rudiment of the air bladder moved from the anterior part to the posterior part of the peritoneal cavity. But the rudiment of the ventral fin did not appear throughout the larval development. From the examination on the collected specimens, it is shown that most of the fish grow over 30mm in total length and mature in a year, and the life span is over one year