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Phytoplankton supports fisheries and aquaculture production. Its vital role as food for aquatic animals, like mollusks, shrimp, and fish cannot be overemphasized. Because of its contribution as a food source for fish, the growth kinetics of Microcystis aeruginosa, a dominant cyanobacterium in the lake, was studied. The regular occurrence of M. aeruginosa is experienced during the months of May to July or from September to November in Laguna de Bay, the largest freshwater lake in the Philippines. M. aeruginosa was collected from Laguna de Bay, isolated, and established in axenic conditions. Data on the growth kinetic parameters for nitrate-nitrogen and phosphate-phosphorus utilization by M. aeruginosa gave the following values: half-saturation constant (K s ), 0.530 mg N. L −1 and 0.024 mg P. L −1 respectively; maximum growth rate (μ max ), 0.671. d −1 and 0.668. d −1 respectively; maximum cell yield, 6.5 and 6.54 log, cells. ml −1 respectively; nutrient level for saturated growth yield, 8.71 mg N. L −1 and 0.22 mg P. L −1 respectively; and minimum cell quota (Q 0 ), 2.82 pg N. cell −1 and 0.064 pg P. cell −1 respectively. The low K s value and high maximum growth rate (μ max ) for phosphorus by M. aeruginosa would suggest a high efficiency of phosphorus utilization. On the other hand, the high K s value for nitrogen indicated a low rate of uptake for this nutrient.

Macrobrachium rosenbergii (de Man 1879) juveniles (0.4 g) were cultured in experimental cages (L × W × H: 2.5 × 1 × 1 m) in Laguna de Bay, the largest lake in the Philippines. The following stocking densities at four replicates each were used: 15, 30, 60 and 90 prawns m−2 of cage bottom. The mean sizes at harvest after 5 months of culture ranged from 14.3 g for the highest stocking density to 26.3 g for the lowest. The mean size at harvest, daily growth rate and size class distribution were significantly influenced by stocking density, with those at the lowest stocking density showing significantly better growth and overall proportion of larger prawns. Heterogeneous individual growth (HIG) was fairly evident in all treatments. The percentage of blue‐clawed males was not influenced by treatment but the mean weight was significantly higher in the lower stocking densities. Both the percentage and mean weight of berried females were significantly higher in the lowest stocking density. Survival was the highest in the lower stocking densities (55.3%, 54.0%, 52.7% and 36.9% for 15, 30, 60 and 90 prawns m−2 respectively). Feed conversion ratio (FCR) improved with decreasing stocking density, ranging from 2.1 to 3. As expected, yield per cropping increased with stocking density and ranged from 450 to 1089 g m−2 yr−1 of actual cage area. Production values obtained in the cage cultured M. rosenbergii were comparable to or even higher than those reported from pond culture, given that the stocking densities used in this study were generally higher than in ponds. The results show that the farming of M. rosenbergii in cages in lakes is a viable alternative to pond culture and has the potential of improve aquaculture production in lakeshore fish farming communities.

Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stocking densities: 10, 20, 30 and 40 shrimp m À 2 . Another set of shrimp was stocked in concrete tanks as reference samples at 30 shrimp m À 2 . Signi¢cant di¡erences were observed among stocking densities throughout the 95-day culture. The ¢nal weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m À 2 and reference tanks were observed respectively. There were no signi¢cant di¡erences in survival throughout the culture period, ranging between 69% and 77%. Daily growth rates (range: 0.11^0.24 g day À 1 ) and speci¢c growth rates (range: 3.54^4.34%) also di¡ered signi¢cantly among stocking densities, both increasing with decreasing stocking density. The feed conversion ratio in the cages did not di¡er among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest followed the equation y 5 81.06x À 0.54 (R 2 50.938) and that of stocking density and production (in g m À 2 ) is y 5 58.01x À 0.46 (R 2 50.834).

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