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:P₂O₅) 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.

A feeding experiment was conducted to determine the effect of a commercial growth promoter, Bayo-n-ox, on Nile tilapia fingerlings (mean initial weight 3.6 g). After 6 weeks, the weight gain of fish given 25 mg Bayo-n-ox/kg body weight was somewhat higher than that of the control fish. A slight growth depression was manifested by fish given 50 mg Bayo-n-ox/kg body weight. Total length followed a trend similar to that of weight gain. However, growth, the feed conversion ratio and the survival rate were not significantly different (p > 0.05) among treatments.

Bighead carp (10.5 months old) stocked in cages in Laguna de Bay were assigned the following feeding treatments: 1. 40% protein diet, 2. 20% protein diet, and 3. no artificial diet (control), to determine the effects of feeding on growth and reproduction. The fish were fed for 15 months. Growth was monitored for the first 9 months and fish were induced to spawn in the succeeding months. Both weight gain and increase in total length did not differ significantly (P > 0.05) among treatments. Results of the induced spawning showed that fish fed the 40%-protein diet had the highest mean total weight of eggs/female, total number of eggs/spawning, and number of eggs/kg body weight. Fish fed the 20%-protein diet had intermediate values while the control fish had the lowest values for the same parameters. However, mean fertilization rates (54–58%) and hatching rates (61–78%) were not significantly different (P > 0.05) among treatments. The mean number of 3-day old fry of fish fed the 20%-protein diet (48 085) was lower than that of fish fed the 40%-protein diet (86 806). The control fish gave a significantly low (P < 0.05) number of 3-day old fry (37 469). When deprived of food for up to 10 days, fry of the fed broodstock had a lower mortality rate than fry of the control fish.

The importance of the analysis of low level nitrite concentrations in aqueous samples is increasing in various fields such as environmental, food, and aquaculture chemistry. Recent progress in ion chromatography paved the way to the direct analysis of nitrite in water samples at ppm to sub ppb levels. However, analysis of low level nitrite in highly concentrated salt matrix still remains a difficult problem. The presence of a large amount of the matrix ion makes establishment of an ion exchange equilibrium very difficult in the column, often resulting in bad peak shapes [1]. In previous papers, we reported the analysis of a nitrite and other anions in chloride matrix on a conventional low capacity anion-exchange column by means of a heart-cut and recycling method [1] and by using a potassium chloride eluent [2]. To monitor the nitrite peak, both a UV detector and a conductimetric detector has been used [3]. Several groups have demonstrated the potential of an electrochemical detector for a specific and sensitive detection of nitrate. [4-6]. Poly(vinyl alcohol) (PVA) gel have been introduced recently as a chemically stable HPLC column packings [7-9]. It was found that when an acidic eluent was employed, a PVA gel and its acylated gel columns produced large capacity factors for nitrite [10].

Penaeus japonicus nauplii from wild spawners were reared up to the early postlarval stage (PL20) in 12-t concrete tanks. A survival rate of 13-15% was obtained. Hatchery-reared postlarvae were restocked in concrete tanks for grow-out. After six months, survival rate was 49.3% with mean body weight of 20 g and carapace length of 21-33 mm. Ablated and unablated females were stocked together with males at 1:1 sex ratio in broodstock tanks. After three months, 11% of the ablated prawns spawned whereas 1.4% of unablated females spawned after five months. Nauplii from these spawnings were reared up to the adult stage thus completing the life cycle of J. japonicus in captivity.

The relationship of predator size to maximum prey size, and predator weight to weight of prey consumed among cannibalistic sea bass (Lates calcarifer Bloch) in a hatchery were assessed. Maximum prey size was computed from morphological measurements (predator mouth width, prey body depth and fish total length), while prey consumption was determined from predators kept in experimental beakers and fed only prey sea bass for a 7-day period. Maximum prey size was 61–67 % of predator total length \((TL_{prey} = 0.5944 TL_{predator} + 0.0724)\). Gut dissection of predators showed that size of ingested prey increased with increasing predator size not exceeding the maximum size limit indicated by the above equation. Daily prey consumption of predators in the beakers was expressed as \(W_{Prey} = -0.2407\; W_{predator^{2}}+ 0.7697W_{predator}-0.1141\). During hatchery rearing of sea bass, fish with length differences of more than 33 % must be separated and food of appropriate size provided to limit cannibalism.

The benefits of intensive farming of the giant tiger prawn Penaeus monodon in the Philippines are discussed in relation to the environmental costs. Ecological effects include mangrove conversion into ponds; use of antibiotics and chemicals leading to drug resistance; dumping of pond effluents which affect neighboring ecosystems; and pumping of groundwater that causes saltwater intrusion and vulnerability to floods. In addition, these effects lead to social costs in the form of reduction in domestic and agricultural water supplies; decreases in the production of foodfish and other food crops; further marginalization of coastal fishermen; displacement of labor; and credit monopoly by big businessmen. Comparative economic analyses of three prawn-farming systems showed that, compared to extensive and intensive culture, semi-intensive farms give the best performance using undiscounted (payback period, return on investment) and discounted (net present value, internal rate of return) economic indicators. With a 20% fluctuation in inputs or selling price intensive farming will no longer be profitable because of the high variable cost. The paper concludes with recommendations for strict enforcement of existing government guidelines (e.g. ban on mangrove conversion); institution of new policies on the use of groundwater, seawater and public credit; diversification of cultured species; and emphasis on semi-intensive farming parallel with brakes on further intensification of prawn farming.

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 (BOD₅), ammonia (NH₄-N) and nitrite (NO₂-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. BOD₅ 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.

A preliminary study was conducted to determine growth and survival of Clarias macrocephalus fed live zooplankton (Artemia or Moina macrocopa ) and/or a dry artificial diet. The specific growth rate over a 14-day rearing period was higher for fish fed Artemia plus a dry diet than for other treatment groups fed either live zooplankton or a dry artificial diet alone. C. macrocephalus larvae can directly take dry diet during the early days of exogenous feeding, however, continued feeding on dry artificial diet resulted in poor fish growth and survival. Mortality due to observed cannibalism in fish fed exclusively an artificial diet increased from 4% to 18% during the last two days of the rearing period. A significantly lower proportion of mortality due to cannibalism was observed in those fed an artificial diet after a 7-day period of feeding on Artemia . The survival rate was generally high, except for the fish fed a dry diet alone.

Fifteen day old sea bass larvae were acclimated to 10‰ S and fed ad libitum levels of Moina, Artemia or Moina + Artemia (at 1:1 ratio). Fish kept at 32 ‰ S and fed Artemia served as a control. After 20 days, specific growth rates of fish ranged from 8.8 ± 2.5%/ day to 12.9 ± 1.4%/day and did not differ significantly in any of the treatments (P > 0.05). Survival rates of fish fed Artemia in either 10 (26.9 ± 8.4%) or 32 (30.2 ± 12.8 %)‰ S and Moina+Artemia (7.7 ± 2.8%) were similar and higher than the Moina-fed group (2.6 ± 1.4%). Results seemed to relate to poor utilization of Moina by younger sea bass (15-day-old). In another experiment, the amount of Moina ingested in the presence or absence of Artemia by 15-, 20-, 25-, 30-, and 35-day-old sea bass was determined. Thirty-day-old sea bass fry ingested the highest number of Moina, whether with (17.19 ± 1.96) or without (25.29 ± 2.93) the addition of Artemia, than did the other age-groups (P < 0.05). There was a low feeding incidence of Moina by 15-day-old sea bass. The number of ingested Moina was positively correlated (r = 0.6358) to the fish body length. The amount of Moina ingested by sea bass of the same age group was not influenced by the length of time after feed introduction. Moina can be used as partial or complete substitutes for Artemia, provided they are sieved beforehand for efficient utilization by the younger sea bass larvae.