Journal of the Marine Biological Association of India

Volume 31 Issue 1&2

Larvae of Crossorhombus valde-rostratus (Alcock) and C azureus (Alcock) (Heterosomata : Pisces) collected during the International Indian Ocean Expedition and Naga Expedition.

C. B. Lalithambika Devi

Larvae of Crossorhombus valde-rostratus (Alcock) and C. azureus (Alcock) containing post-flexion stages ranging in size from 6.0 mm to 12.9 mm SL and 7.5 mm to 18.8 mm SL respectively were found in the zooplankton collected during the International Indian Ocean Expedition (IIOE) (196-605) and Naga Expedition (1959-61).

The flat leaf-like body, continuous dorsal and anal fins with soft rays, presence of spines (serrations) on posterior basipterygial processes and their absence on cleithra and urohyal distinguish the larvae from others. The larvae of C. azureus and those of C. valde-rostratus resemble very closely with each other in general shape and meristics. But they can be distinguished by the presence of a tiny spinous process on the urohyal at its anterior end in C. azureus. The larval stages of both these species are reported and described for the first time.

In the Indian Ocean the larvae of C. valde-rostratus appear to prefer open ocean, found in the stratum sampled during day time as well as during SW monsoon period whereas C. azureus showed a decided liking to coastal or nearshore waters and occurred in the stratum mostly during night. However they also preferred SW monsoon season as the other species. Naga samples also showed identical preferences in so far as diel variation is considered but they, were mostly found in open ocean. A significant negative correlation was found between the distribution of C. valde-rostratus and the dissolved oxygen values indicating their tolerance to low oxygen concentrations.

Date : 31-12-1989