Description and ontogeny of young Stolephorus baganensis and Thryssa kammalensis, two Engraulididae from Peninsular Malaysia

Abstract

The morphology of the digestive system was useful to distinguish the larvae of Stolephorus baganensis and Thryssa kammalensis before the full development of their dorsal and anal fins. The relative positions of these fins, the length of the anal fin, and body depth, were good criteria for identifying individuals >10·0 mm LS. For both species, the relative growth of the ten morphometric characters studied was best explained by linear piecewise regressions indicating inflection in allometry at specific standard lengths. Most of these sudden changes in growth rate occurred between 6·9 and 10·0 mm LS for S. baganensis and between 5·8 and 8·9 mm LS for T. kammalensis. Double‐centred principal component analysis (PCA) confirmed important changes in the external morphology of both species during this transition period. Prior to this period, the main parameters characterizing the global morphological changes of both species were the length and position of dorsal and anal fins whereas they were body depth and eye diameter (only in S. baganensis) for larger specimens. Complete development of scales did not appear as a suitable criterion to define the end of the larval period, which, instead, was set at the size at which larvae presented an adult‐like pigmentation (respectively 35·0 mm LS and 55·0 mm LS in S. baganensis and T. kammalensis).