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New pond fertilization recommendations set

Mississippi producers, previously relying on 60-year-old recommendations from Alabama to fertilize ponds in preparation for young catfish, are now seeing good results with updated recommendations made for local soils.

Fish producers fertilize nursery ponds to stimulate the growth of oxygen-producing algae. The phytoplankton become food for zooplankton, tiny animals eaten by catfish fry — those less than 1 inch long. Fertilizer is used to alter the nutrient content of the water, making it more desirable for this tiny plant and animal life.

Chuck Mischke, water quality scientist with the Mississippi Agricultural and Forestry Experiment Station, evaluated phytoplankton and zooplankton response to fertilization in channel catfish nursery ponds.

“We found that ponds responded more to nitrogen than to phosphorus additions, and increasing the nitrogen application had better results,” Mischke said. “Based on these studies, the recommended fertilization practices for Mississippi Delta catfish ponds were changed.”

Ponds are fertilized to stimulate a good algae bloom that produces oxygen ponds need to help foster shade, which, in turn, helps prevent rooted plants from becoming established and interfering with harvest. Fertilization also encourages a good zooplankton population.

Mischke said dramatically changing pond fertilization practices should improve fry growth, survival and health. The research, prompted by the number of Mississippi producers having difficulty getting consistent algae blooms, encouraged Mischke to begin looking at what was being recommended to add to ponds.

“We're still fine-tuning those recommendations, and we'll study catfish ponds in east Mississippi next,” Mischke said. “Following the new recommendations that take into account Delta soils, we are seeing much quicker phytoplankton bloom, more consistent blooms and preferable forms of algae and zooplankton.”

David Wise, MAFES fisheries biologist, said there are no studies in actual production ponds comparing fish production results of the former fertilization recommendations with current ones. However, the new recommendations are very efficient at producing phytoplankton blooms.

“We used to have problems getting good blooms,” Wise said. “You've got to have two good blooms on the pond, one of phytoplankton and one of zooplankton. You need the color from the phytoplankton to shade out the pond and prevent too much growth of algae and pond plants.

“The zooplankton bloom is a food source for the fry. Fertilizing the pond properly optimizes the conditions for the zooplankton to grow,” he added.

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