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.

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Subang Lake (3°1oN, tot°29'E) is a stratified lowland reservoir with a marked chemocline of some variables that probably contributes to a greater species diversity and vertical layering of plankton communities . Destratification occurs in the reservoir and is probably seasonal . Destratification results in toxic and deoxygenated waters as well as nutrient replenishment from the hypolimnion and could cause sudden mass fish and zooplankton mortality and consequent algal blooms . The nutrient budget study indicates that the reservoir is naturally oligotrophic with phosphate as a limiting factor and the high nutrient loading of the auxiliary water intake from a nearby river, Buloh River, is the cause of eutrophication in the reservoir.

This paper describes the use of a continuous-flow chamber for maintaining small and fragile fish larvae and their prey in a healthy state and under suitable conditions over a 24 h period for studies on prey preferences. Survival of golden perch (Macquaria ambigua Richardson) larvae and prey was high and ten replicates on food preferences were carried out simultaneously. The larvae preferred small Daphnia carinata King (780-860 rm) over larger ones (2000-3120 and 3680-5440 gm) and preferred cladocerans (Daphnia carinata King and Moina micrura Kurz) over calanoids (Boeckella de Guerne & Richard). The chamber is also suitable for studies on feeding behaviour and diet requirements of fish larvae.