Effects of golden perch (Macquaria ambigua (Richardson)) larvae, fry and fingerlings on zooplankton communities in larval-rearing ponds: An enclosure study

Abstract

In the absence of fish, the plankton community in enclosures in a larval-rearing pond showed a marked successional pattern from rotifers and Moina to copepod and then Daphnia-calanoid dominance. The impact of growing larvae and fry, with densities of 40-118 m-2 at harvest, on zooplankton was conspicuous only after Day 22 when Daphnia became rare and calanoid numbers were suppressed. Predation by fry caused reductions in the size of Moina, cyclopoids and calanoids found. An increase in Daphnia size, 'gigantism', occurred because of limitations in the mouth gape of the fry. Low densities of fingerlings (0.65 g wet weight and stocked at 1 and 2 m-2) had little effect on zooplankton succession, whereas high density (15 fingerlings m-2) caused a shift to a zooplankton community dominated by small cladocerans, rotifers and cyclopoids. High fingerling density also caused a reduction in the size of the microcrustaceans found. The size and density of fish determined their impact on zooplankton composition and succession, demonstrating that similar starting times and consistency in fish density are necessary in obtaining 'sensible' statistical inferences in field fish-zooplankton experiments.