Ontogeny of growth, respiration and feeding rate of the freshwater calanoid copepod Eudiaptomus graciloides

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Abstract
The calanoid copepod, Eudiaplomus graciloides, was reared from egg to adult on uni-algal diets (0.1. 0.5 and 2.5 mg dry wt 1−1) using the green alga, Chlamydomonas reinhardtii, as food, or on a mixed diet consisting of Lake Esrom water filtered through a plankton net with pore size 45 μm and supplemented with C. reinhardtii (2.5 mg dry wt 1−1). On the mixed diet at 21.0°C growth in body dry wt (W, μg dry wt) was exponential, and the growth constants were 0.21 day−1 in the early to mid juvenile stage (N1 - C4) and 0.11 day−1 in the late juvenile to early adult stage (C4-A). At 14.5°C the corresponding growth rate constants were 0.10 and 0.08 day−1. Similar growth rates were found at uni-algal concentrations of 0.5 and 2.5 mg dry wt I−1, and it was argued that the threshold concentration for growth in Eudiaptomus was close to 0.1 mg dry wt I−1. The clearance (C, ml h−1) of copepodites was measured on the uni-algal diets. The constants of the regression (C = aWb) were: a = 0.125, b = 0.858 (2000 C. reinhardtii ml−1), a = 0.068, b = 0.849 (10 000), a = 0.028, b = 0.875 (50 000). Ingestion rates were calculated from the clearances and the average algal concentrations. At the three food levels the average daily rations were 30, 67 and 125% of body dry wt. The respiration rate (R, nl O2 h−1) was measured in individuals reared on the mixed diet. The constants of the regression (R = aWb) were: a = 4.82, b = 1.07 (nauplii, 14.5°C), a = 4.17, b = 0.904 (copepodites and adults, 14.5°C), a = 6.87, b = 0.757 (copepodites and adults, 21.0°C). No significant difference in the respiration rate of copepodites reared on uni-algal diets and the mixed diet could be demonstrated. Energy budgets were calculated. The assimilation efficiency and the gross growth efficiency of copepodites decreased markedly with increasing food concentration, the net growth efficiency varied from an average of 0.44 at the lowest algal concentration to 0.60 on the mixed diet. The results are discussed in relation to previous findings with both freshwater and marine copepods.

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