Comparative water quality and channel catfish production in earthen ponds and a biofloc technology production system

Authors: Green, Bartholomew - Bart; McEntire, Matthew - Matt

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2016
Publication Date: 2/16/2017
Citation: Green, B.W., McEntire, M.E. 2017. Comparative water quality and channel catfish production in earthen ponds and a biofloc technology production system. Journal of Applied Aquaculture. 29(1):1-15.
DOI: https://doi.org/10.1080/10454438.2016.1261751

Interpretive Summary: Pond management strategies to produce food-size catfish are varied and have evolved over time towards increased intensification as exemplified by the increasing adoption by farmers of the split-pond system. The biofloc technology (BFT) production system could represent a further intensification of catfish culture. In the outdoor BFT production system a complex of living organisms, including phytoplankton and bacteria, closely associated with particulate organic matter that is maintained in suspension in the water column by continuous aeration metabolizes ammonia excreted by the intensively fed fish. Consequently, high yields can be obtained in response to high stocking and feeding rates, and good water quality can be maintained. In traditional earthen pond culture algal photosynthesis is the primary source of dissolved oxygen; mechanical aeration is used at night to maintain dissolved oxygen concentration above critical levels. And, phytoplankton uptake is the principal sink for excreted TAN. Thus, the objective of this 210-day study was to evaluate variation in water quality and fish growth for channel catfish stocked in earthen ponds or the BFT production system. Feed input and culture environment resulted in water quality dynamics that varied between treatments. Chlorophyll a concentration, an indicator of algal biomass, increased rapidly after stocking in the BFT system in response to high feed input, whereas in ponds concentrations did not begin to increase until day 60. Algal uptake and bacterial nitrification were the two processes that utilized excreted feed nitrogen (ammonia). In ponds, algal uptake predominated and little nitrification occurred, whereas in the BFT system both algal uptake and nitrification functioned to keep ammonia concentrations low. Fish in both treatments grew rapidly throughout the study, but at harvest fish from ponds were significantly larger than those from the BFT system. Size classes of harvested fish from ponds were skewed towards the larger market sizes, whereas in the BFT system size classes were skewed towards the smaller market sizes. Despite differences in the size-class composition of harvested fish, gross fish yield was higher in the BFT system because of the greater stocking rate. Density-related social interactions appear to have affected catfish growth more in the BFT system and need to be identified and resolved.

Technical Abstract: This 210-day study was conducted to compare variation in water quality and fish growth for channel catfish stocked in 0.04-ha (228 m3) earthen ponds or 18.6-m2 (15.7-m3) biofloc technology (BFT) production system high density polyethylene-lined rectangular tanks. Channel catfish (Ictalurus punctatus) fingerlings (47 g/fish) were stocked into ponds at 1.5 fish/m2 (14,820 fish/ha) and into BFT tanks at 12.6 fish/m2 (126,000 fish/ha). Fish were fed a 32% protein commercially extruded feed daily to apparent satiation. Feed input and culture environment resulted in water quality dynamics that varied between treatments. Chlorophyll a concentration, an indicator of algal biomass, increased rapidly after stocking in the BFT system in response to high feed input, whereas in ponds concentrations did not begin to increase until day 60. Phytoplankton uptake and nitrification were the two processes that utilized excreted feed nitrogen (ammonia-nitrogen). In ponds, phytoplankton uptake predominated and little nitrification occurred, whereas in the BFT system both phytoplankton uptake and nitrification functioned to keep ammonia-nitrogen concentrations low. Fish in both treatments grew rapidly throughout the study, but at harvest fish from ponds were significantly larger than those from the BFT system. Size classes of harvested fish from ponds were skewed towards the larger market sizes, whereas in the BFT system size classes were skewed towards the smaller market sizes. Despite differences in the size-class composition of harvested fish, gross fish yield was higher in the BFT system because of the greater stocking rate. Density-related social interactions appear to have affected catfish growth more in the BFT system and need to be identified and resolved.