Ontogenetic development during changeover from an endogenous to exogenous nutritional source in Laotian cyprinid <Emphasis Type="Italic">Cirrhinus microlepis</Emphasis> larvae

The nutritional transition process from endogenous to exogenous feeding in larvae of the Laotian indigenous cyprinid Cirrhinus microlepis was investigated approximately 200 h after hatching. Although 17 characters were observed, emphasis was given to those associated with the onset of feeding and subsequent development of feeding ability. Growth of larvae was divided into two phases, rapid growth (to 71.5 h) and slower growth (from 71.5 h). The yolk absorption pattern was divided into four phases, the rapid yolk consumption (to 21 h), slow yolk consumption (to 71.5 h), complete yolk consumption (to 118.5 h) and post-yolksac phases. Onset of feeding was observed at the end of the slow yolk consumption phase (71.5 h after hatching), and notochord flexion, appearance of caudal fin supports/rays and gut coiling were observed at the same time. Comparisons of developmental characters relevant to the onset of feeding between C. microlepis and sympatric species, including Trichogaster pectoralis, Anabas testudineus and Pangasianodon hypophthalmus, revealed that morphological features related to the nutritional changeover were most likely linked to the habitat environment and survival strategy of early larvae.