Studies on larval euphausiids from the southwest coast of India with notes on their developmental pathways and breeding seasons

Abstract

In spite of the exhaustive studies done the world over on the larval euphausiids, the developmental pathways of several species remain unknown or partly understood. The fact that larval euphausiids form a sizable portion of the zooplankton in the sea makes a study of the larval biology more important. A large number of zooplankton samples collected from the southwest coast of India have been examined for the occurrence and the developmental stages of some major species of euphausiids. As a result of the studies the complete post-naupliar stages of l'seudeupausia latifrons, Euphausia diomedeae, E. sibogae, E. lenera, Nematoscelis gracilis, Stylocheiron armatum and S. affine have been obtained. The full complement of post-naupliar stages of S. affine has been identified and the developmental pathway has been traced for the first time. Critical discussions have been made in the article on the various life history stages of important species. A study on the occurrence and abundance of the larval stages in the different months have enabled to understand the active breeding seasons of five of the species. Thus it has been found that Pseudeuphausia latifrons, E diomedeae and S. armatum have an active breeding season from December to April while E. sibogae and S. affine have it from August to December and October to February respectively. S. affine has been found to be a continuous breeder.