Precilla F. Subosa

Performance of recirculating systems for prawn hatchery and broodstock maturation tanks

Abstract The potential use of recirculating systems with facilities for waste removal for prawn ( Penaeus monodon ) hatchery and broodstock maturation tanks was investigated. Recirculating systems evaluated for larval culture tanks were biological filtration and zigzag stream sedimentation. Systems using airlift and airstones as aeration devices with partial water change but with no provision for recirculation served as control. Results showed successful rearing of Penaeus monodon (nauplii-postlarvae) in systems with facilities for wastewater recirculation. Aeration systems became ineffective in maintaining acceptable water quality as shown by increases in 5-day biochemical oxygen demand (BOD 5 ), ammonia (NH 4 N) and nitrite (NO 2 N) nitrogen, and decreases in dissolved oxygen (DO). For broodstock maturation, a recirculating system with a preconditioned biological filter was compared with a flow-through system. Biological filtration proved to be useful in meeting water quality requirements. Nitrification was satisfactory with ammonia levels lower than 1·0 mg liter −1 . The pH values in the biofilter effluent were maintained at 7·8–8·3. BOD 5 levels were below 10 mg liter −1 while DO tended to drop due to the nitrifying activity of the filter. Better reproductive performance of Penaeus monodon broodstock was obtained in the recirculating system than in the flow-through system.

Evaluation of organic and inorganic fertilizers in brackishwater milkfish ponds

The study was conducted in twelve 144-m2 ponds to evaluate the effect of different organic and inorganic fertilizers on the growth, survival, gross production, and profitability of marketable milkfish. The following treatments were used: Treatment I, SEAFDEC traditional fertilization practice (16-20-0 at 50 kg/ha and 45-0-0 at 15 kg/ha); Treatment II, half-dosage of Treatment I; Treatment III, chicken manure at 0.5 ton/ha; and Treatment IV, MASA (processed from agricultural and industrial wastes) fertilizer at 0.5 ton/ha. All treatments were applied once in every 2 weeks. No significant difference (P > 0.05) existed in the harvest and production of milkfish among the treatments. However, economic indicators such as return-on-investment (ROI), payback period, and marginal analysis ranked the performance of the fertilizer treatments in the order of I, II, III and IV. Fish kills occurred in three ponds applied with chicken manure and MASA fertilizer. This could have been due to a heavy build-up of organic matter in the pond bottom which led to the collapse of the benthic algal community, depletion of dissolved oxygen and the presence of hydrogen sulfide. It is therefore suggested that a lower dosage of organic fertilizer should be applied in ponds especially during the rainy season.

Changes in shrimp feed quality and effects on growth and survival of Penaeus monodon juveniles

Abstract Five practical shrimp diets were formulated to contain 1, 10, 20, 50, and 100 g tetraethoxypropane (TEP) kg −1 diet. A diet with no added TEP served as the control. Diets were fed to Penaeus monodon (average weight 4.84 ± 0.11 g) juveniles to determine the level of fat oxidation tolerable to shrimp. Changes in shrimp feed quality were monitored by physical evaluation, thiobarbituric acid (TBA) values, fatty acid composition, and histological examination. Effects of feed quality on growth and survival of shrimp were evaluated. Results showed significant differences ( P −1 diet, showed signs of physical deterioration after 6–8 weeks. This diet had a significantly higher TBA value (1262 mg malonaldehyde kg −1 fat) than the other treatments. The unsaturated fatty acid content of the diet decreased as its TEP content increased. Weight gains of shrimp fed diet 5 (50 g TEP kg −1 diet) and diet 6 were significantly lower than those fed the other diets while survival was similar. Hepatopancreatic lesions were not evident in all samples. Fat oxidation levels expressed in terms of TBA values of up to 828 mg mal kg −1 fat can be tolerated by Penaeus monodon juveniles in terms of growth response.

Chicken manure, rice hulls, and sugar-mill wastes as potential organic fertilizers in shrimp (Penaeus monodon Fabricius) ponds

Shrimp (Penaeus monodon Fabricius) were cultured (3000 juveniles/ha) in 50-m2 earthen ponds fertilized with composted agricultural and industrial wastes at a basal application rate of 2 ton/ha. The following materials were tested: chicken manure, rice hulls, and three types of sugar-mill wastes: mudpress, boiler ash, and bagasse. After 66 days significant differences existed among treatments (P < 0.05) in mean body weight and gross production of shrimp. A significantly higher mean body weight (28.8 g) was obtained with boiler ash than with chicken manure (26.05 g) and these were followed by mudpress (25.8 g) and rice hulls (25.05 g) which were not significantly different from each other. The mean body weight using bagasse (22.0 g) was significantly lower than in the other treatments followed by the control (no fertilizer, 19.6 g). High survival rates were obtained in all treatments. The pond yields ranged from 53.7 to 86.4 kg/ha after 66 days with daily weight increments of the shrimp ranging from 0.18 to 0.41 g.

Butylated hydroxytoluene : its effect on the quality of shrimp diet stored at various temperatures and on growth and survival of Penaeus monodon juveniles

Abstract Shrimp diets with and without the antioxidant, butylated hydroxytoluene (BHT) were stored at 10°, 20°, 28°–30°, and 40°C for 10 weeks. To monitor lipolysis and lipid oxidation, free fatty acid (FFA) content, peroxide values (PVs), and malonaldehyde (MAL) levels were measured from the extracted lipids of the stored diets. Fatty acid levels of the diets increased between the initial and final samplings and the increase was higher (8.4%) in diets without BHT stored at 40°C after 10 weeks. Peroxide values of the extracted lipids were low and fluctuated monthly between 2.2 and 7.4 mmol/kg fat. MAL levels increased in diets with and without BHT except those stored at 10°C for 4 weeks. Diets with BHT stored at 10°C had the lowest (8.7 mg MAL/kg fat) MAL levels and diets without BHT stored at 40°C for 10 weeks had the highest (16.9 mg MAL/kg fat). Shrimp fed diets with BHT gained 5.7–6.4× their initial weight after 10 weeks of rearing. Their growth was significantly better than those fed diets without BHT (4–6×) during the 60-day culture period. Survival was significantly higher in those fed diets with BHT (87–88%) than those without BHT (75–85%). No hepatopancreatic lesions were seen in shrimp samples fed diets with and without BHT and stored at various temperatures. The incorporation of BHT in shrimp feed is necessary if the feed is to be stored at 40°C for 10 weeks.

Yield of Penaeus monodon Fabricius in brackishwater ponds given different fertilizer combinations

Abstract Yields of Penaeus monodon Fabricius in brackishwater earthen ponds were determined using different fertilizer combinations in two sets of experiments. Results indicated that the use of fertilizers was vitally needed to sustain growth of shrimps at a stocking density of 5000 individuals/ha. Application of urea (45-0-0) and diammonium phosphate (18-46-0) fertilizers at nitrogen to phosphorus fertilizer rates (N:P 2 O 5 ) of 15:15 and 30:15 kg/ha, together with 1 t/ha of chicken manure, was inexpensive and resulted in better yields. In another experiment, increase in the amount of nitrogen and phosphorus fertilizers did not significantly improve prawn yields, but did increase the cost of production. Different salinity levels affected survival in both experiments.