Development of Eodiaptomus japonicus Burckhardt (Copepoda, Calanoida) reared on different sized fractions of natural plankton

Abstract

The nutritional value of different sized fractions of natural plankton was investigated for the growth of Eodiaptomus japonicus Burckhardt by comparing the development of its naupliar and copepodid stages fed on differentially fractionated planktonic assemblages of a eutrophic pond, at 20°C. Water filtered through a 0.8 μm Nuclepore filter, containing mainly small coccoid bacteria (0.45-0.6 μm in cell diameter), at a concentration of 82.7 μg C l-1 could not support the development of E. japonicus. The 3 μm filtered water, containing bacteria and picoalgae, at a total concentration of 259 μg C l-1. supported development but not egg production. The 20 μm filtered water, containing bacteria, pico-algae and large algae, at a total concentration of 2600 μg C l-1, supported rapid development of the juveniles and continuous egg production by the adults. The separated 3-20 μm fraction, containing only large algae, could not support the development at concentrations of 131 and 196 μg C l-1. However, the same rapid development of the juveniles and continuous egg production by adults occurred at all of the tested concentrations between 261 and 3920 μg C l-1 of the large algae. The results suggest that E.japonicus favours algae larger than 3 μm during its complete lifespan, and that the threshold food concentration for its development varies between 200 and 250 μg C l-1.