Publication Date:
2021-07-20
Description:
Long-term fluctuation, diel changes and spatial differences in water quality were intensively studied in two 0.4-ha channel catfish (Ictalurus punctatus) ponds in northwest Mississippi. The "traditional" pond was managed with the common "emergency" aeration system using a paddlewheel aerator while the "experimental" pond was aerated continuously with a new diffused aeration system. Aside from the difference in aeration, both ponds were managed as similarly as possible. Both ponds were stocked at 20,000 fish/ha and harvested after a four month growing period. Water samples were taken at two different sites at the surface and bottom in each pond using a new sampling technique to avoid artificial mixing of the water column during the sampling. Daytime stratification was observed in the "traditional" pond, but never in the "experimental" pond. During stratification water quality (water temperature, dissolved oxygen, pH, total ammonia-nitrogen and nitrite-nitrogen) differed significantly between surface and bottom waters. In both ponds differences in water quality between sites at the same depth were always negligible. Diel cycles of water temperature, dissolved oxygen, pH, total ammonia-nitrogen and nitrite-nitrogen were documented in both ponds. Water temperature, dissolved oxygen and pH were highest in the late aftemoon and lowest in the early moming hours; in contrast, total ammonia-nitrogen and nitrite-nitrogen concentrations were highest during nighttime and lowest in the late aftemoon. The cycles were generally related to the periodic metabolic activity of phytoplankton influenced by solar radiation. Diel cycles were verified in two 7-ha commercial channel catfish ponds. Long-term changes in water quality were related to changes in solar radiation and phytoplankton biomass. In general, both ponds showed similar long-term fluctuations. A cold spell in fall separated the investigational period in two parts. Phytoplankton densities were highest in the warmer period and lowest in the colder. Inorganic nitrogen concentrations were lowest during the warmer period and highest during the colder period due to changing assimilation rates of phytoplankton. Phytoplankton densities and soluble reactive phosphorus concentrations were higher in the experimental pond than in the traditional, and is related to the aeration system. The experimental aeration system provided better dissolved oxygen and nitrification conditions. Fish growth and production data indicated better growth conditions in the experimental pond, but further research, with sufficient replication will be needed to prove this.
Type:
Thesis
,
NonPeerReviewed
Format:
text
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