THE EFFECT OF TEMPERATURE, AND FOOD QUANTITY AND QUALITY ON THE GROWTH AND DEVELOPMENT RATES IN LABORATORY-CULTURED COPEPODS AND CLADOCERANS FROM A SRI-LANKAN RESERVOIR

Length growth, instar durations, fecundity and mortality rates of five species of microcrustacean zooplankton from a tropical reservoir were measured in relation to food quantity and temperature in laboratory c ultures. Three cladocerans (Ceriodaphnia cornuta, Moina micrura, Diaph anosoma excisum), one calanoid copepod (Heliodiaptomus viduus), and on e cyclopoid copepod (Mesocyclops thermocyclopoides) were studied. Filt ered seston (45 mu m mesh) from a local pond was used for food. Two fo od concentrations were employed: (1) 10 mu g chlorophyll l(-1) (ca 0.2 5 mg Cl-1), and (2) 50 mu g chlorophyll l(-1) (ca 1.25 mg Cl-1). Food levels and water temperature (22.5, 27.5, and 32.5 degrees C) used, ro ughly covered the ranges found in the reservoir. Although all the thre e growth parameters were often affected to some degree by temperature and food, the quantitative response of the species differed. Also, the species reacted differently to the three possible interactions (i.e. food x temperature, food x instar, and temperature x instar). This con tributed to the overall differences in the species responses. For the cladocerans, instar durations were always affected by temperature. The food did not affect the duration time of the adults and that of the c ombined juvenile instars, the latter except in one case significantly. For the two copepods food level affected the duration times of naupli ar and copepodite instars, but the effect of temperature was only sign ificant for H. viduus. The development times observed for H. viduus we re extraordinary long compared with values reported in the literature for other tropical calanoids. This suggests that food conditions in ou r culture were adversely affecting its growth rates.