The diurnal vertical variation of ichthyoplanktonic abundance was investigated on May 21-22,1994, at a 65 m deep fixed station (25°12'N, 121°20'E) situated 7 km offshore from the mouth of the Tanshui River, Taiwan. Temperature was stratified at noon but was homogeneously distributed during the remainder of the day. A similar distribution pattern was found also in salinity profiles. The density of ichthyoplankton ranged from 126 to 3167 ind/1000 m3. The highest density occurred in bottom water at 0100 and a fairly even distribution occurred in mid-water. A total of 5,860 ichthyoplankton specimens was collected and 222 species, or species groups belonging to 82 families, were identified. Sardinops melanostictus was the most abundant, making up 7.2% of the total catch. The next four most abundant species were Callionymus huguenini (5.1%), Mene maculata (4.7%), Auxis spp. (4.3%) and Therapon jarbua (3.8%). The dendrogram from the clustering method of unweighted pair-group method using arithmetic averages (UPGMA) exhibited three assemblages: mid-night (0100), afterdark (1900) and daytime (0700 and 1300). The former two assemblages were grouped as the nighttime assemblage because they were similar, and the dominant species were Leiognathus rivulatus, Setipinna tenuifilis, Ctenotrypauchen microcephalus, gobiid and ophichthid. The daytime assemblage was primarily composed of Scomberoides Iysan, Therapon jarbua, Sardinops melanostictus, Upeneus bensasi, and Holocentrus sp.
Larval fish, Diversity, Length frequency
