Now showing items 1-4 of 4

    • Article

      Contribution of natural food and supplemental feed to the gut content of Penaeus monodon Fabricius in a semi-intensive pond system in the Philippines 

      U Focken, A Groth, RM Coloso & K Becker - Aquaculture, 1998 - Elsevier
      Juvenile Penaeus monodon were stocked in grow-out ponds and fed a compound diet at high rates for 19 weeks under semi-intensive conditions. At three stages of the rearing period (weeks 6, 11 and 16), the gut content of the shrimp was analysed microscopically at every hour of the day. Additionally, possible sources of natural food (lablab, lumut, zoobenthos, etc.) were analysed microscopically and where possible for proximate composition. At week 6, the gut content consisted of 28.9% supplemental feed, 42.3% plant materials (other than from the pelleted diet), 1.8% crustacean parts and 27.0% diverse detrital matter. For week 11, the percentages (same order) were 47.5%, 21.1%, 22.8%, 8.6% and for week 16, 21.7%, 34.3%, 31.7% and 12.9%, respectively. Food preference did not change with time of the day. At week 6, most feeding activity occurred at night, later, feeding activity shifted to day-time. Reduction of the maximum gut content at dissolved oxygen levels below 4 mg l−1 at night indicated a cessation of feeding in which case shrimp fed during the day-time, when dissolved oxygen levels were higher.
    • Article

      Diurnal feeding pattern and gut content of milkfish Chanos chanos (Forsskål, 1775) cultured semi-intensively during the wet and dry season in brackish ponds in the Philippines 

      KJ Kühlmann, U Focken, RM Coloso & K Becker - Aquaculture Research, 2008 - Blackwell Publishing
      To improve feeding management and reduce feed cost in semi-intensive grow-out culture of milkfish (Chanos chanos, Forsskål 1775) in brackish ponds, the relative shares of natural food (NF) and supplemental feed (SF) ingested by the fish were microscopically quantified from their completely dissected digestive tracts sampled during 24-h cycles in wet (June–September) and dry (December–April) seasons. Particles from rice husk, indigestible to milkfish, were used as internal markers to quantify supplemental feed. Significantly (P<0.05) more NF than SF (1.4±0.2 vs. 0.4±0.1 g kg−0.8) and SF than NF (1.4±0.8 vs. 0.6±0.3 g kg−0.8) were found during the first month of the wet and the first 3 months of the dry season respectively. Diurnal feeding patterns on SF were significantly higher at morning hours during the dry compared with the wet season. The feeding pattern of milkfish is likely to be affected by the different weather and pond conditions in both seasons. Developing a season-specific pond fertilization management to enhance NF availability in semi-intensive milkfish culture can help to improve the economical and ecological performance of milkfish culture.
    • Article

      Effects of low nitrogen-phosphorus ratios in the phytoplankton community in Laguna de Bay, a shallow eutrophic lake in the Philippines 

      ML Cuvin-Aralar, U Focken, K Becker & EV Aralar - Aquatic Ecology, 2004 - Springer Verlag
      The effects of low nitrogen-phosphorus ratios on microalgae from a large eutrophic freshwater lake in the Philippines were investigated. Natural microalgal populations from Laguna de Bay, the largest lake in the Philippines, were cultured using three different nitrogen-phosphorus weight ratios (2N:1P; 6N:1P and 12N:1P) at two phosphorus concentrations (0.25 and 0.5 mg l–1) in each case. The growth and genera composition of the cultures under the different treatments were followed for a 12-week period. Community level responses were assessed based on species richness (s), Shannon-Wiener Index (H’), Simpson Index (λ) and Evenness (J’). Among the different microalgal groups, only the chlorophytes showed a significantly higher density in response to the 12N:1P treatment at the higher P concentration, indicating that the nutrient ratio had a significant interaction with the nutrient levels used in the experiments. The genera found in the different treatments were generally similar; however, the degree of dominance of some varied with treatment during the experiment. The succession of dominant genera also differed among the N:P treatments. The diatoms like Fragilaria, Aulacoseira (= Melosira) and Nitzschia dominated the lowest N:P. On the other hand, chlorophytes (Kirchneriella and Scenedesmus) dominated the highest N:P treatment, particularly from the second to the seventh week of the experiments with the diatoms becoming co-dominant only towards the eighth week until the end of the experimental. The 6N:1P treatment showed a mixed dominance between the diatoms and the chlorophyte genera. The various indices of diversity indicate significantly lower diversity only in the 12N:1P at 0.5 mg l–1 P and not in 12N:1P at 0.25 mg l–1 P.
    • Article

      Microcystins in natural blooms and laboratory cultured Microcystis aeruginosa from Laguna de Bay, Philippines. 

      ML Cuvin-Aralar, J Fastner, U Focken, K Becker & EV Aralar - Systematic and Applied Microbiology, 2002 - Urban & Fischer Verlag
      Laguna de Bay, the largest freshwater lake in the Philippines, experiences periodic blooms of the cyanobacteria Microcystis aeruginosa. Blooms of these cyanobacteria in 1996, 1998 and 1999 were sampled. HPLC and MALDI-TOF mass spectrometry were used to analyze for microcystins. A total of 16 structural variants of the toxin were isolated from the samples with microcystin LR (MC-LR) as the most abundant variant in the samples from 1996 and 1999 making up 77 to 85% of the total, respectively. MC-RR was the dominant variant in the 1998 bloom making up 38%. The samples from 1996 had the highest total toxin concentration (4049 µg g-1) followed by those from 1998 (1577 µg g-1) and 1999 (649 µg g-1). A strain of M. aeruginosa previously isolated from the lake was also cultured in the laboratory under different nitrogen concentrations (1, 3 and 6 mg L-1) and elevated phosphorus concentration (0.5 mg L-1) to determine the influence of these factors on toxin production. A total of 9 different structural variants of microcystin were isolated from the laboratory cultures with MC-LR consisting more than 75% of the total in all treatments. No significant differences in the total toxin concentration as well as the % distribution of the different variants among treatments were observed. However, the strain of M. aeruginosa cultured in the laboratory had from 3 to 20 times higher total microcystin than those harvested from the lake.