Larvae and juveniles of two engraulid species, Thryssa setirostris and Thryssa hamiltonii, occurring in the surf zone at Trang, southern Thailand

 Engraulid larvae and juveniles collected from the surf zone off the Sikao River, Trang, southern Thailand, in the period between August 1999 and September 2000 were identified as Thryssa setirostris (n = 249, 14.1–25.7 mm SL) and T. hamiltonii (n = 731, 15.2–22.2 mm SL), based on the number of lower gillrakers and maxilla morphology. The two species were easily distinguishable by the melanophore pattern distributed on the anterior part of the striated hindgut, T. setirostris possessing three to five melanophores along the ventral midline and T. hamiltonii lacking such melanophores. The ratios of head length and eye diameter to SL also differed between the species, both being higher in T. hamiltonii. The distribution of the two species was limited to the surf zone outside the river mouth, that region being characterized by a higher salinity than the river and its tributaries.