I wish to express my sincere gratitude to Mr. O. Nakken, leader of the “Pelagic Fish Assessment Survey North Arabian Sea” for making this study possible, for many useful discussions and for valuable comments on the manuscript.
I also wish to thank the captain, the crew and the scientific staff participating on R/V “Dr. Fridtjof Nansen” for collecting samples of the mesopelagic fauna.
Thank is also due to Miss I.M. Beck for able assistance through all phases of this study, to Mr. H. Ullebust for drawing the figures and to Miss. J. Silchenstedt for typing most of the manuscript.
I am much indebted to Dr. B.G. Nafpaktitis for identifying part of the Diaphus species collected.
