EFFECTS OF GOLDEN PERCH (MACQUARIA-AMBIGUA (RICHARDSON)) LARVAE, FRY AND FINGERLINGS ON ZOOPLANKTON COMMUNITIES IN LARVAL-REARING PONDS - AN ENCLOSURE STUDY

In the absence of fish, the plankton community in enclosures in a larv al-rearing pond showed a marked successional pattern from rotifers and Moina to copepod and then Daphnia-calanoid dominance. The impact of g rowing larvae and fry, with densities of 40-118 m(-2) at harvest, on z ooplankton was conspicuous only after Day 22 when Daphnia became rare and calanoid numbers were suppressed. Predation by fry caused reductio ns in the size of Moina, cyclopoids and calanoids found. An increase i n Daphnia size, 'gigantism', occurred because of limitations in the mo uth 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 succes sion, whereas high density (15 fingerlings m(-2)) caused a shift to a zooplankton community dominated by small cladocerans, rotifers and cyc lopoids. High fingerling density also caused a reduction in the size o f 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 necess ary in obtaining 'sensible' statistical inferences in field fish-zoopl ankton experiments.