|Distribution of bacteria in a biofilter-equipped, semi-closed intensive fish culture unit|
(1992). Distribution of bacteria in a biofilter-equipped, semi-closed intensive fish culture unit, in: Progress in aquaculture research: proceedings of the 4th German-Isreali Status Seminar held on October 30-31, 1990. Spec. Publ. Eur. Aquacult. Soc, 17: pp. 55-78
In: (1992). Progress in aquaculture research: proceedings of the 4th German-Isreali Status Seminar held on October 30-31, 1990. Spec. Publ. Eur. Aquacult. Soc, 17. European Aquaculture Society: Oostende. ISBN 90-71625-11-7. 360 pp., more
In: Spec. Publ. Eur. Aquacult. Soc, more
Microbial studies were done on a semi-closed recycling intensive fish culture system. equipped with an aerobic (biofilter) and an anaerobic (denitrifier) water treatment units. Total number of bacteria (TBN), the frequency of dividing bacteria cells (FDC) and the percentage of bacteria showing respiratory activity (as measured by INT-reaction) were determined at nine sites in the culture system. The bacteria population of both the aerobic and anaerobic treatment units were also compared using scanning electron microscopy. TBN differed by orders of magnitude between sample sites in spite of intensive hydrolic mixing within the system (e.g. 106 bacteria ml in water flowing into the 10 -1 fish basin and 10 bacteria ml-1 in the sand-water mixture within the anaerobic treatment unit). Dividing bacteria cells (FDC) were difficult to detect anywhere in the system, even Where high loads of organic material should provide abundant bacterial nutrients. Water from the outflow of the aerobic treatrnent unit showed similar results of TBN (1x108 bacteria ml-1) and portions of INT-active bacteria (12- 13%) as did effluent from the denitrifying unit. INT-active bacteria were most abundant inside the biofilter (18% of TBN) and in fish basin effluent (19% of TBN). Microbial parameters varied only slightly during a 24 h cycle. In the two treatment units microbial colonization differed in both cornposition and quant i t y. Probable colonles of ammonia-oxydizing bacteria were detected within the biofilter. No such colonles were seen in the anaerobic unit. Nitrogen compounds (NH4-N. NO2-N and NO3-N) were sampled simultaneously at three sites. Ammonia showed a periodicity corresponding to the expected metabolic activity of the fish, varying from 0.02 -0.46 mg L-1 in the morning to 0.54 -2.45 mg L-1 in the evening. During the 24 h cycle transformation of NH4-N through NO2-N to NO3-N was inefficient (1.0- 3.5 mg L-1 NO2-N and 5.0- 23.6 mg L-1 NO3-N). For their efficient removal, both the aerobic, but especially the anaerobic treatment units should be optimized. Neither the additions of fish feed or fluctuations in ammonia levels had a noticeable effect on the total number of bacteria or the proportion of dividing or respiring bacteria cells. However, some specialized groups of microorganisms, may have been affected.