Experiments were conducted to evaluate the efficacy of five live organisms (Artemia, Brachionus calyciflorus, Chironomus plumosus, Moina macrocopa and Tubifex sp.) and an artificial diet (40% protein) in the larval rearing of Asian catfish Clarias macrocephalus. The larvae were fed three times daily starting at the onset of exogenous feeding. Results showed that the catfish larvae utilized the live organisms more efficiently than the artificial diet. The Tubifex-fed larvae consistently showed the highest growth rate. In trial 1, length increment (64.9 mm), weight gain (3192 mg) and specific growth rate (13.1%) after 8 weeks of feeding were significantly higher (P < 0.05) in catfish larvae given Tubifex than those in all other treatments. In trial 2, length increment after 4 weeks of feeding was highest in larvae fed Tubifex (22.9 mm) although it did not significantly differ from that of larvae given Moina (21.0 mm). However, weight gain of larvae fed Tubifex (253.0 mg) was significantly higher than that of larvae fed Moina (171.6 mg). The specific growth rate was highest for larvae fed Tubifex (15.0%) followed by larvae fed Artemia (14.5%), Moina (14.4%) and Chironomus (12.0%). Survival rates of the catfish larvae ranged from 9 to 39% after 8 weeks in trial 1 and from 26 to 83% after 4 weeks in trial 2. The present results suggest that Tubifex is an excellent food and a potential substitute for Artemia in the rearing of catfish larvae.

KEY WORDS: Chlorella, cobalt, culture, rotifer, vitamin B 12 .All forms of animals require inorganic elements or minerals for their normal and healthy life processes. Therefore, many minerals play an important role in animal nutrition, including aquatic animals like fish. 1 Cobalt (Co) is known as a constituent mineral of vitamin B 12 (VB 12 ), having cyanocobalamin (C 63 H 88 CoN 14 O 14 P) as a representative compound. VB 12 is a type of water soluble vitamin, which is essential for maintaining normal and healthy physiological conditions for both terrestrial and aquatic animals. VB 12 can be manufactured only by microorganisms like gut bacteria, and natural sources are entirely of animal origin. Therefore, it is a common technique for fish farmers to add Co compounds as a material for synthesizing VB 12 in the gut and enhance the dietary value of the fish feed by satisfying their VB 12 requirement. 1-3 In zooplankton, the function of VB 12 for promoting growth performance was previously investigated in rotifer. 4-7 However, no study has been conducted so far on the supplemental effect of Co for zooplanktons including rotifer, despite its importance in aquaculture. In this paper, the authors preliminarily investigated the supplemental effect of Co compound into rotifer feed for enhancing its production performance.Marine rotifer Brachionus rotundiformis (mean lorica length ± standard deviation [SD] of matured individual: 192.5 ± 13.8 µm) was used for the experiment. The stock-cultured rotifer was inoculated into triplicated 850 mL glass bottles (working volume: 800 mL) at densities of 240 ind/mL. The rotifer was cultured under natural photoperiod at 30°C with ordinary aeration in full seawater condition (salinity 33 psu). As rotifer feed, VB 12 -free Chlorella vulgaris cultured in the laboratory using 5 L jar-fermentors were supplied. The cultured Chlorella was centrifuged to the concentration of 10 10 algal cells/ mL and stored at 5°C until used for the experiment. The Chlorella concentrate was fed once a day in the morning at a ratio of 50 000 algal cells/rotifer per day, based upon the optimum feeding ratio reported in previous papers. [8][9][10][11] The VB 12 contents of VB 12 -free Chlorella and sea water used for the experiment were confirmed to be 0.0 pg/mL by bioassay using Lactobacillus delbrueckii. 2 The supplemental effect of dietary Co compound was investigated as follows. As the Co source, cobalt (II) sulfate heptahydrate: CoSO 4 ·7H 2 O was used. The concentration of dietary Co compound was decided from a preliminary experimental result: 4-day-batch trial with duplicate treatment, 238.3, 939.8 and 582.1 ind/mL were obtained as the mean final densities of the rotifers from 250 ind/mL inoculum for 0, 0.01 and 1.0 mg/mL Co supplemented feed groups, respectively (unpubl. data, T Higuchi 2002). Co compound was dissolved into distilled water and mixed into Chlorella concentrate to establish the dietary concentrations of 0, 0.001, 0.01 and 0.1 mg/mL, and fed to the rotifers. Also, acute toxicity of the co...

The study compared the species composition of phytoperiphyton ("lab-lab") present in ponds when gradually filled with water weekly to depths of 5, 10, 15 and 30 cm between the wet and dry seasons, for one month before the stocking of fish was studied. This was done during the dry season (March-April, 2003) and wet season (June-July, 2002). Periphyton was allowed to grow on 24 artificial substrates set at equal distances in a 1000 m 2 pond. "Lab-lab" that colonized the artificial substrates and that on the pond surrounding the substrates were scraped off from a measured surface area. Simultaneously, water was collected for the analysis of physical, chemical and biological parameters. Sampling was done bi-weekly coinciding with 2 and 7 days submergence at a desired depth before adjusting the water level. The major algae consisted of the diatoms (Bacilliarophyta), the blue green algae (Cyanobacteria), and the green algae (Chlorophyta). The diatoms were dominant during the dry season while the cyanobacteria dominated during the wet season. Twenty eight genera were observed during the dry season and 25 genera were noted in the wet season. Variation in genera and density that were observed every sampling period, was influenced by environmental conditions and the incoming water. The total algal density ranged from 100.7×10 8 -855.1×10 8 and to 24.7×10 8 -83.9×10 8 organisms.m −2 during the dry and wet seasons, respectively.