Two consecutive experiments were conducted to study the e¡ects of stocking density on growth, food utilization, production and farming pro¢tability of Nile tilapia (Oreochromis niloticus) ¢ngerlings (initial mean weight:16.2 AE 0.2 g) fed Azolla, as a main component in diet. In experiment 1, ¢sh were hand-fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g À1 ) diets A30, A35 and A40 containing 30%, 35% and 40% Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by-products. No signi¢cant di¡erences were found in growth parameters and production (P40.05). Total investment cost was signi¢cantly higher with A30 (Po0.05), but same pro¢tability values were obtained with all diets (P40.05). In experiment 2, three stocking densities, 1, 3 and 5 m À 2 , were assigned to three treatments T 1 , T 2 and T 3 respectively. Fish were hand-fed twice daily with diet A40. The ¢nal mean weight (89.53^115.12 g), the mean weight gain (0.811.10 g day À1 ), the speci¢c growth rate (1.90^2.20% day À1 ) and the apparent food conversion ratio (1.29^1.58) were a¡ected by stocking density, with signi¢cant di¡erence (Po0.05) at 5 m À 2 , compared with the other densities. Stocking density did not affect survival rate (P40.05).Yield and annual production increased with increasing stocking density, ranging from 7.10 AE 0.90 to 25.01 AE 1.84 kg are À1 and 28.79 AE 3.66 to 101.42 AE 7.48 kg are À1 year À1 , respectively, with signi¢cant di¡erences between all densities (Po0.05). Higher stocking density resulted in higher gross return and lower cost of ¢sh production, with signi¢cant variations (Po0.05). The net return increased with increasing stocking density (Po0.05). However, both densities of 3 and 5 m À 2 produced the same pro¢tability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 ¢sh m À 2 with A40 to improve production and generate pro¢t for nutritional security and poverty alleviation in rural areas.

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Production dynamic and chan e of fatty acid and amino acid contents of the freshwater rotiferBrachionus calyciflorus Pallas f e l o n Dicryospbaerzum chlorelloides were investigated in batch and semicontinuous culture systems. The mean daily roduction was 57.4 and 34.2 mg of rotifers I-'&' (wet weight) respectively and were highly depen&nt o n initial algal cell density. The rotifer fed on algae contained high amounts of linoleic acid (18 : 2n-6) and amino acids such as arginine. The suitability of rotifers for gud eon Gobio gobzo L. and perch Percafluviatilis L. larvae during their early feeding stage was investigatei. After a 10-day experiment, larvae fed with rotifers grew significantly faster than those fed on micro-encapsulated dry food. The best food conversion and protein efficiency ratio were observed with the larvae fed with rotifers. Combining rotifers with micro-encapsulated dry food better improved growth rate and food utilization in perch than did the dry food alone. Zusammenfassung Nabwert des RadertiercbensBrachionus calyciflorus Pallas fur die Aufzucbt von Laruen von Supwasserfischen Die Produktionsdynamik und die Variation des Amino-und Fettsaure ehaltes von mit der Griinalge Dicryos{bae+m chlorelloides gefiitterten Sul3wasserridertierchen Brackonus calyciflorus Pallas wurden in ontinuierlichen und halbkontinuierlichen Kultursysternen untersucht. Die durchschnittliche Tagesproduktion lag bei 57.4 bzw. 34.2 mg Rotatorien I-'&' (Trockengewicht) und hing stark von der Ausgangsdichte der Algen ab. Mit Algen gefiitterte Radertierchen wiesen einen hohen Gehalt an Linoleinsauren (18 : 2n-6) und solchen Arninosauren wie z. B. Arginin auf. Den Nahrwert der Rotatorien wurde fur die Larven des friihen Entwicklungsstadiurns von Grundling Gobio obio L. und Barsch Percaflm&ztilis L. untersucht. Nach 10 Ta en zeigten jene mit Radertierchen gefutterten Larven eine signifikativ hohere Wachstumsrate als solcie die mit Trockenfutter ernahrt wurden. Die beste Nahrungskonversion und Proteinausbeute zeigten mit Rotatorien gefiitterte Larven. Irn Verhaltnis zur ausschliei3lichen Verfiitterung von Trockennahrung an Larven des Barschs brachte auch die Kombination von Trockennahrung und Radertierchen eine deutlich bessere Wachstumsrate und Nahrungsausbeute.

Postlarvae (PL) of Macrobrachium rosenbergii (de Man 1879) were stocked at 1, 2, 3 and 4 PL m−2. Prawns were fed only pellets (P) and a combination of pellets and snail meat (PS) with three replications in 100 m2 plots in the rotational prawn–rice system. Water levels were 0.3–0.6 m in rice growing areas. The water temperatures at noon in the hot months were higher than the suitable range for prawns. The final mean weights of prawns in treatments 1, 2 and 3 PL m−2 were significantly higher than in treatment 4 PL m−2 (P<0.05). The yields from different density treatments ranged from 194±82 to 373±32 kg ha−1 and increased significantly with the increases in prawn densities (P<0.05). There was no significant difference between the two types of feed on production parameters (P>0.05). The total cost significantly increased at higher densities (P<0.05), but it was not different between feed types (P>0.05). Net profit and cost benefit ratio of treatment PS were significantly higher than in treatment P. In the present study, treatment 3 PL m−2 and treatment PS offered the optimal results.

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