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UBC Theses and Dissertations

The effects of fish waste and oxytetracycline on the microbenthos Wu, Henry C.


Fish feed, feces and oxytetracycline (OTC) were added to sediment microcosm tanks in 1990, and the physical and biological changes in the benthic environment were followed over a period of 28 days. The main objective was to study the response of the microfauna (benthic microbial and protozoan communities) to fish waste. Results indicated that anoxic and highly reducing conditions were quickly reached in the sediments within a day, with a shift away from microbially mediated sulphate reduction to methanogenesis in the degradation of fish waste. Most of the OTC was quickly washed out of the fish waste when added to the sediments, with small quantities of theantibiotic persisting throughout the duration of the study. Bacterial abundance rapidly increased in the sediments when fish waste and oxytetracycline were added. While there was a potential for OTC to act on the microfaunal communities, this effect could not be conclusively demonstrated. A second study was conducted in which fish feed, feces and oxytetracycline were added gradually to sediment microcosm tanks in 1991 for 20 days. The main objective of this study was to examine the changes in the physical-chemical regime and the benthic microfaunal community over time. The gradual addition of fish waste to the sediments resulted in microbially mediated sulphate reduction being the main route for the degradation of fish waste. As most of the oxytetracycline was quickly washed out of the fish waste, the amount of the antibiotic was insufficient to affect the bacterial and protozoan communities. There were two rapid increases in ciliate abundance, with the initial bloom occurring before the increase in bacterial abundance, and the decrease in the ciliate population was correlated to increased reducing conditions in the sediments. A large number of heterotrophic microflagellates developed after the ciliate population declined, and these flagellates were observed to be actively grazing on the bacterial population. The short time interval of the study was considered to be insufficient for noticeable changes to have occurred in the meio- and macrofauna. The rapid response of the microfauna to fish waste suggests that changes in the protozoan community could be used as a biological tool in monitoring the impact of fish waste on the environment. More efficient management at aquaculture facilities could minimize environmental problems.

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