Browsing by Author "Becker, Klaus"
Contribution of natural food and supplemental feed to the gut content of Penaeus monodon Fabricius in a semi-intensive pond system in the Philippines 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.
Species and proximate composition of Laguna de Bay phytoplankton cultured in three different nitrogen-phosphorus ratios and their utilization by Nile tilapia ML Cuvin-Aralar, U Focken, K Becker & CB Santiago - In Conservation and Ecological Management of Philippine Lakes in Relation to Fisheries and Aquaculture: Proceedings … Seminar-Workshop held on October 21-23, 1997, INNOTECH, Commonwealth Ave., Diliman, Quezon City, Philippines, 2001 - Aquaculture Department, Southeast Asian Fisheries Development Center; Philippine Council for Aquatic and Marine Research and Development (PCAMRD), Department of Science and Technology; Bureau of Fisheries and Aquatic ResourcesNatural phytoplankton populations from Laguna de Bay were used in outdoor batch culture experiment in 1-ton capacity circular concrete tanks and 60-liter glass aquaria for a maximum duration of 72 days. The treatments consisted of the following nitrogen-phosphorus ratios: 2N: 1P, 6N: 1P, and 12N: 1P. The growth and species composition of phytoplankton were monitored in each of the three treatments. The phytoplankton were partially harvested at weekly intervals. The proximate composition of the freeze-dried harvest was also analyzed. The freeze-dried harvest was also used to feed Nile tilapia Oreochromis niloticus (L.) to determine effects of the different N-P ratios on the utilization of phytoplankton by fish. The fish were fed isonitrogenously and ration ranged from maintenance requirement for the first week to 3 times maintenance requirement for the succeeding weeks. Results showed that green algae, particularly the Chlorococcales group, dominated all the cultures. This was followed by diatoms. The blue-green algae consisted the third group in all treatments. Gross energy, crude protein, crude fat, neutral detergent fiber and crude ash content of the phytoplankton harvest did not vary significantly among treatments. However, crude protein expressed as percentage of organic matter was significantly higher in the treatment using 12N: 1P compared to those cultured in lower N-P ratios. Nile tilapia fed phytoplankton from 12N: 1P and 6N: 1P ratios showed significantly better growth than those fed with phytoplankton cultured in the lowest N-P ratio.