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We report the results of controlled feeding trials on the tiger shrimp, Penaeus monodon (Fabricius). The desired colour was obtained by feeding a diet supplemented with astaxanthin (50 p.p.m) for 7± 8 weeks before harvest. Similar coloration was achieved, however, by including in the feed an algal material (Dunaliella salina) that contains bcarotene but no astaxanthin. Feed containing bcarotene at 125 p.p.m also gave the required coloration at 7±8 weeks, whereas the same results was obtained after only 5±6 weeks when feed containing 175 p.p.m b-carotene was used. Irrespective of whether the shrimp were fed astaxanthin or b-carotene, the main carotenoid accumulation was astaxanthin, in free and esteri®ed form, showing that P. monodon has the metabolic ability to convert b-carotene into astaxanthin. The supplementation with b-carotene or astaxanthin had no signi®cant effect on growth, average ®nal weight, survival rate or feed conversion ratio, nor on the immune response of the shrimp in terms of production of haemocytes phenoloxidase in the cytoplasmic granules of the haemocytes, microbial clearance ability and resistance to infectious diseases. This is a highly signi®cant development for commercial aquaculture, because it shows that supplementing diets with b-carotene can achieve the same result as doing so with much more expensive astaxanthin.

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A¯atoxin B 1 was studied in juvenile black tiger shrimp (Penaeus monodon Fabricius) (1±2 g) to see the effects on growth performance and histopathology, and in adult shrimp (10±12 g) to study the effects on immuno-physiological function, histopathology and a¯atoxin residue. Feeds supplemented with 0, 50, 100, 500, 1000 and 2500 p.p.b. a¯atoxin B 1 were given to test groups for an 8-week period. A¯atoxin B 1 in the diet showed highly negative correlation to average weight, weight gain and survival (r = ± 0.99, ±0.96 and ±0.95 at P < 0.05, respectively)

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The objective of this experiment was to evaluate soy-protein-concentrate (SPC, 65% protein) as a replacement ingredient for ®shmeal (FM, 65% protein) in shrimp diets. Shrimps (Penaeus monodon, PL-15) were raised in the laboratory to 1.5 g body weight and were then transferred into 120-L aquaria with water temperature maintained at 28 T 2°C. Five isonitrogenous and isocaloric diets (protein 36%, ME 15.7 kJ g ±1 ) were prepared using SPC at inclusion levels of 0, 8.75, 17.50, 26.25 and 35% by replacing 0, 25, 50, 75 and 100% of the FM from the diet, respectively. All diets contained 12% soybean meal. The diets were randomly assigned to 45 aquaria (n = 9), each containing 30 shrimps. Shrimps were fed to satiation four times a day for an 8-week period and were exposed to alternating 12 h light and dark periods. Aggregate body weight for each aquarium was recorded every 2 weeks, when shrimps were also counted.The feed intake by shrimps was not different at 0, 25 or 50% FM substitution levels, but was signi®cantly decreased at 75 and 100% substitution levels. The body weight gains of shrimp fed diets with 0, 25 or 50% FM substitution were signi®cantly better than those fed diets with 75 or 100% FM substitution. A 100% substitution of FM from the diet had a severe negative effect on the body weight gain. With increasing substitution of FM with SPC, the feed ef®ciency ratio, protein ef®ciency ratio, and protein and fat gain in the shrimp followed the same general pattern as described for body weight. Mortality was not signi®cantly different among the dietary treatments. These data indicate that a 17.5% inclusion of SPC in the diet of P. monodon can support normal growth of the shrimp with the potential for substituting FM.

Bottom soil samples were collected from 35 ponds in the vicinity of Samutprakarn, Thailand. Ponds ranged in age from 3 to 39 years and had been used continuously for production of tilapia. Liming materials had been applied in large amounts, and bottom soils of all ponds had pH above 7, low exchange acidity, and free carbonate. Pond soils often contained between 1% and 2% total sulphur, suggesting that they were potential acid–sulphate soils. However, acidity from sulphide oxidation was not expressed because carbonate in the soil neutralized it. Concentrations of total carbon seldom exceeded 4% and the average for organic carbon was 1.90%. The correlations between pond age and both total carbon and organic carbon concentration were weak (r=0.34 and 0.36 respectively). Concentrations of nitrogen in bottom soils did not differ with pond age and ranged from 0.1% to 0.3% with an average of 0.19%. The average ratio of concentrations of carbon and nitrogen was 11. Acid‐extractable phosphorus concentrations averaged 217 mg kg−1, but the phosphorus adsorption capacity averaged 768 mg kg−1 suggesting that soils still have considerable reserve capacity to adsorb phosphorus. Ponds can be used annually for semi‐intensive production of tilapia, and presumably other species, for many years without serious deterioration of bottom soil quality.