We express our gratitude to Jose Thekkan for the facilities provided. Special thanks are due to C.V. Midhu for giving access to the specimens and also for her assistance in studying the anatomy. We are grateful to N.V. Benny, C.A. Varghese and P.J. Jostin for help during collection of specimens. Thanks are also due to R. Pethiyagoda for help and support during this study. Help rendered by H.H. Ng, K.C. Gopi and K. Remadevi is also acknowledged here. Special thanks are also due to K.T. Teji, A. Gopalakrishnan, P.R. Divya and V.S. Basheer for the help and support rendered by them. Finally, we thank J.G. Lundberg, C.J. Ferraris, Jr., and Y. Iwatsuki for their valuable comments and suggestions. While planning and executing the experiments presented here, we took care not to violate the national and international laws and guidelines for the use of fishes in research.