Early life history of a catadromons sculpin in western Japan

To clarify the early life history of Cottus kazika (Cottidae), the ontogeny , osteology distribution, migration and food habit were examined based on l arvae and juveniles collected from coasts and estuaries in western Japan. T he sequence of fin completion was pectoral (P-1)-dorsal soft-ray part (D-2) -anal (A)-dorsal spine part (D-1)-pelvic (P-2). However, that of calcificat ion was P-1-P-2-D-1-D-2-A. Larvae and juveniles of C. kazika are distinguis hed from those of coastal sculpins of Japan by large preopercle spines, con spicuous parietal spines, the large and densely pigmented pectoral fin and the relatively deep body. C. kazika and Myoxocephalus polyacanthocephalus p lus Enophrys bison share these four ontogenetic characters. From the relati onship between the growth ring count on the sagittae and total length, the size of embryos at hatching is estimated at 5.2 mm. Larvae are estimated to reach 7 mm in 10 days, 9 mm in 20 days and 11 mm in 30 days after hatching . Hatching dates for larvae collected in the Shimanto estuary in 1987 peake d during the period around the new moon in January. Many free embryos rangi ng from 4.3 to 5.9 mm were collected using an aqualamp at a rocky shore out side the Yura River mouth, at high salinity (> 33 ppt), but none were colle cted in the estuary. From beach samples, seasonal changes in body size vari ed from year to year, and no consistent growth pattern was found, although juveniles were generally larger in late March and April than in January and February. Very few larvae were collected along shorelines where there were no adjacent rivers. Food habit of larvae and juveniles changed with growth . Polychaete larvae, cladocerans and copepods were found in preflexion larv ae less than 6 mm. Gammarids were one of the important food items for larva e over 6 mm. Juveniles over 12 mm almost exclusively fed on gammarids. In t he Shimanto estuary,larvae and juveniles stayed near the river mouth in Jan uary and February, within a stagnant layer where temperature and salinity r emained about 12 degrees C and 20 ppt, respectively. Juveniles tended to mo ve in March when the stagnant layer disappeared in the estuary.