We present length–weight relations (LWR) and use rapid, low-cost histological methods to describe the reproductive biology of the red-bellied fusilier, Caesio cuning (Bloch, 1791), and the longfin emperor, Lethrinus erythropterus Valenciennes, 1830, based on 137 and 139 specimens, respectively, collected from a remote area in Papua New Guinea.  The LWR for C. cuning is W = 0.0208FL3.0322.  We estimate male L50 at 12.6 cm FL and female L50 at 15.3 cm FL.  Overall sex ratio of mature individuals is not significantly different from 1 : 1; however, sex-ratio does vary with length.  Females dominate size-classes from 17 through 20 cm and males are more abundant in smaller and larger size classes. The species is a batch-spawning gonochore.  Batch fecundity is an exponential function of length BF = 0.1163FL4.2796. The LWR for L. erythropterus is W = 0.0145FL3.0976 for all specimens, but the length–weight relation differs between sexes.  We estimate minimum size-at-maturity for males at 19.2 cm FL, and female L50 at 20.4 cm FL.  Overall sex ratio of mature individuals is not significantly different from 1 : 1; however sex-ratio does vary with length.  Males dominate size classes > 21 cm.  The species is a batch-spawning, protogynous hermaphrodite.

size-at-maturity, reproductive mode, gonadosomatic index, size-specific sex ratios, batch fecundity, Morobe Province