Growth pattern among the post-naupliar stages of three species of Euphausiacea (Crustacea)

Abstract

Experimental data regarding the larval development in Euphamiacea are very much limited and hence the pattern of larval development and the growth rate are estimated by making use of the material obtained from the open sea. Several methods of estimating the growth have been in use. The author attempts here to demonstrate the growth pattern among the post-naupliar developmental stages of three species namely Euphausia diomedeae Ortmann, E. sibogae Hansen and Stylocheiron armatum Colosi, based on material obtained from the southeastern Arabian Sea. A comparative study has also been made of the pattern of growth among these species. The percentage of increase in body length in the three species mentioned above generally showed considerable decrease as development progressed from first calyptopis onwards. However, considerable variation was observed in the rate of increment in length in between species. It was also found that the larval length and the length in adults are not proportional in the three species. The accuracy of the identity of larval stages and of the larval sequence were verified using the ' Brooks Law' of larval growth. Attention is also drawn to the modern technique of calculating growth rates by the application of log/linear regression equations relating the duration of the intercraoult period to successive moult numbers or body lengths.