Browsing by Author "Focken, U."
Analysing the diel feeding patterns and daily ration of Nile tilapia, Oreochromis niloticus (L.), in Laguna de Bay, Philippines H Richter, U Focken, K Becker, CB Santiago & WB Afuang -
Journal of Applied Ichthyology, 1999 - Wiley-BlackwellCage cultured Nile tilapia, Oreochromis niloticus, were sampled at a commercial set-up on two occasions in 1995 in Laguna de Bay, Philippines, each time over a 24 h cycle. The stomach content weights were averaged for each subsample and analysed with the computer model MAXIMS. The model predicted that, in May, larger fish (mean total weight: 31.5 g) feeding on natural food alone fed continuously from dawn to dusk, ingesting 5.1 % body mass equivalent (% BME, wet weight basis) whereas smaller fish (mean total weight: 9.8 g) had two feeding periods per day, from sunrise to mid-morning and again from mid-afternoon until after sunset, ingesting 13.7 % BME. In August, fish were given supplemental feed once daily at 07:00 h. These fish (mean total weight: 81.7 g) fed intensely until supplemental feed ran out before mid-day, after which some ingestion of natural food took place later in the day. The fish ingested 5.8 % BME supplemental feed and 5.1 % BME natural food per 24 h. In May, most of the stomach contents consisted of the blue-green alga Anabaena spiroides, whereas in August, the natural food was made up principally of detritus.
Feeding ecology of silverperch, Terapon plumbeus Kner, and the impact fish-pens in Laguna de Bay, Philippines M Kock, U Focken, H Richter, K Becker & CB Santiago -
Journal of Applied Ichthyology, 2000 - Blackwell PublishingAquaculture is an important factor in the fishery of Laguna de Bay in the Philippines; fish-pens and net-cages covered ≈10% of the lake surface in the late 1990s. The present study was carried out to assess the possible influences of aquaculture on a wild fish species, silverperch, Terapon plumbeus Kner, with a special emphasis on the feeding ecology of this fish. For the purposes of the investigation, 24-h samples were taken at 2-month intervals close to a fish-pen as well as in open water over a one-year period to acquire more information on this species. Significant differences in standard length and total weight were found between stations and sampling months. In open water, a mean standard length of 53.6 mm and a mean total weight of 4.2 g were found, whereas close to the fish-pen, the corresponding values were 57.6 mm and 5.4 g, respectively. The maximum mean standard length was attained around December 1996 and February 1997 (59.5 mm in open water; 66.1 mm close to the fish-pen), and the minimum was found in June 1996 (49.1 mm in open water; 46.2 mm close to the fish-pen). Noticeable differences were found in the food spectrum between the two sampling stations. Zooplankton, the major food source at both stations, was more important in the stomach content of fish in open water. The same was true for insects (i.e. chironomid larvae), although these did not make up such a large fraction of the diet. On the other hand, close to the fish-pen, aufwuchs-algae, phytoplankton and fish were more important. Generally, benthic organisms were consumed more frequently close to the fish-pen. Zooplankton was more important in the diet of smaller fish. In all size groups, the importance of zooplankton decreased during the rainy season.
Voluntary feed intake and energy partitioning in tilapia, (Oreochromis niloticus) fed diets with different protein/energy levels CB Santiago, U Focken & K Becker - In A Chwalibog & K Jakobsen (Eds.), Energy Metabolism in Animals. Proceedings of the 15th Symposium on Energy Metabolism in Animals, 11-16 September 2000, Snekkersten, Denmark, 2001 - Wageningen PersIn order to investigate the effect of different protein/energy levels of diets (two commercial and one laboratory) on voluntary feed intake and energy partitioning in tilapia (O. niloticus), 15 fishes with an initial body mass of 33 g were reared individually in respirometric chambers for 42 days and offered 3 diets ad libitum. The protein contents of the diets were 36.1, 33.8 and 36.8% (dry matter base); the energy content 18.9, 18.4 and 19.2 kJ GE/g and 11.7, 10.5 and 15.4 kJ ME/g. The initial body composition and energy content was estimated from a control group. Feed consumption was recorded for each individual fish. Body mass development was monitored weekly. At the end of the experiment, the fishes were sacrificed and their chemical composition (protein as N.6.25, lipid, ash) and gross energy content were determined. To establish energy budgets, ingestion (I) was calculated from feed intake, retention (P) from accretion in the carcass, heat production (R) from oxygen consumption (indirect calorimetry) and apparently non-utilized energy (faecal and non-faecal losses, U) by difference from energy ingestion. In the beginning, food consumption amounted to ~5% body mass equivalent (BME) per day for all groups and gradually decreased to 2.5, 2.8 and 1.6% BME by the end of the experiment. While the food consumption was significantly different between the treatments, there were no significant differences in the body mass development. Average final body mass was 98.6, 93.8 and 103.7 g. Energy retention was 29.7, 29.2 and 44.4% of GE ingested; heat dissipation 32.1, 27.9 and 36.0%; faecal and non-faecal losses 38.2, 43.2 and 19.6%. For all energy budget parameters, values for the laboratory diet were significantly different from those of commercial feeds 1 and 2. Calculation of metabolizable energy from ingested feed revealed no significant differences in the energy uptake, suggesting that the voluntary feed uptake was controlled by the demand for metabolizable energy. The fishes were able to completely compensate for the lower ME content of the commercial feeds by increasing voluntary feed intake.