Effect of environmental factors on development of rotifer and copepod nauplii populations in sunshine bass Morone chrysops X M. saxatilis nursery ponds without fish.

摘要

Knowledge of the effect of environmental factors on timing and production of zooplankton populations would enable sunshine bass Morone chrysops X M. saxatilis farmers to stock fry when live food is most available and thereby increase fry survival. Relationships of morning water temperature, morning and average daily air temperature, day length, number of rain days and daily rain fall, and dissolved oxygen concentrations to time required for rotifer and copepod nauplii populations to peak in freshlyfilled freshwater nursery ponds was determined. Relationships of the same independent variables to concentrations of rotifers and copepod nauplii at the peak were also determined. For rotifers, day length, dissolved oxygen, and water and air temperatures were highly correlated with time to the peak density, but not concentration of rotifers. Time required for copepod nauplii densities to peak was associated with rain events; whereas, nauplii concentration was related to day length, dissolved oxygen levels and, to a lesser extent, water and air temperatures. Regression equations of the independent variables had very low predictive value for rotifer or nauplii densities or time to reach initial peak nauplii populations. Regressions of day length, morning water temperature, morning and average daily air temperature had moderate values (r2>0.7) for predicting time to initial peak rotifer densities.