Effects of water hardness and turbidity on growth and fecundity of freshwater Cladoceran, Moina macrocopa (Straus, 1820)

Water hardness and turbidity are important parameters in zooplankton culture, especially for Cladoceran affecting growth and reproductive parameters of the plankton. Effects of water hardness and turbidity on growth and fecundity of the Cladoceran, Moina macrocopa, was investigated by culturing and feeding them on green algae Scenedesmus quadricauda. Experimental treatments for hardness were 0, 20, 40 and 80mg/I as CaCO3 and for turbidity were 0, 20, 40 and 80 NTU (Nephelometric Turbidity Unit). Experiments were carried out in 500m1 flasks with initial density of 15 individuals per flask in randomized complete block design with three replicates. After 10 days, we found that M macrocopa, had the maximum population density (370.5-365.0 individuals per flask), maximum specific growth rate (SGR) (0.35/day), and the shortest population doubling time (Dt) (1.98 days) at 0 and 20mg/1 CaCO3, all with significant differences compared to other treatments (P<0.05). In contrast, we observed the maximum population density (296-325.5 individuals per flask) at turbidities of 0 and 20 NTU, maximum SGR (0.33/day) and the shortest Dt (2.10 days) at turbidity of 0 NTU, with significant differences compared to other treatments (P<0.05). The highest fecundity of Al macrocopa was obtained at 213mgil as CaCO3 and turbidity of 0 NTU which significantly differed with other treatments (P<0.05). Overall, we showed that AI macrocopa in freshwater with hardness less than 20mg11 as CaCO3 and turbidity less than 20 NTU had better growth and fecundity performance. The species can be used to evaluate habitats where water hardness and turbidity is higher. Mass culture of the species based on its growth and reproduction under these optimal conditions could provide suitable zooplanktonic biomass for feeding of fish larvae.

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