|Green, Bartholomew - Bart|
Submitted to: Book of Abstracts Aquaculture America
Publication Type: Abstract only
Publication Acceptance Date: 12/13/2006
Publication Date: 2/26/2007
Citation: Green, B.W., Perschbacher, P., Schrader, K. 2007. Catfish production and water quality in circulated ponds [abstract]. Book of Abstracts Aquaculture America. p. 358. Interpretive Summary: Not required
Technical Abstract: Horizontal discharge, and up-welling and down-welling vertical discharge circulators have been used to manipulate water quality in large water bodies. Circulator-induced impact on lake or reservoir water quality has been variable, particularly in terms of the effect on phytoplankton abundance and species composition. The limited data available on the effect of circulation in channel catfish (Ictalurus punctatus) production ponds indicates that operating a horizontal discharge circulator only during daylight hours had marginal impact on water quality and fish production. Circulator design and duration of operation may increase the impact of circulation. The purpose of this experiment was to evaluate the effect of a horizontal discharge or an up-welling vertical discharge circulator on water quality, plankton and channel catfish production. Twelve 0.1-ha earthen ponds were used for this completely randomized design study. Four ponds each were equipped with a low-revolutions-per-minute (approximately 6 RPM) horizontal discharge circulator or an up-welling vertical discharge circulator. Circulators operated continuously. All ponds were equipped with an electric paddlewheel aerator (0.373 kW) that was activated when pond DO concentration was 4.0 mg/L or less. Control ponds were equipped with only the paddlewheel aerator. Ponds were stocked with stocker catfish at 5,117 kg/ha; mean initial stocker weight was 0.33 kg/fish. Fingerling catfish (0.015 kg/fish) were understocked at 14,820/ha. Ponds were stocked in late January to early February. Fish were fed a 32% protein floating extruded feed daily to apparent satiation (20 min period). Feeding began in early March and reached 112 kg/ha/day by mid-April. Fish growth was monitored in ponds by periodic seine samples. Ponds were harvested during the last week of October. Green algae predominated in all treatments ponds through mid-June, after which blue-green algae predominated until harvest. Chlorophyll a concentrations were similar among treatments, and averaged 240.3, 197.2, and 194.7 mg/m3 for the control, horizontal and vertical circulation treatments, respectively. Off-flavor algae were present in treatment ponds from mid-July through early September. Water quality variable means did not differ among treatments. Temperature and dissolved oxygen concentration profiles, however, were uniform to the 76-cm depth in circulated ponds. Thus, excess photosynthetically produced dissolved oxygen was retained in circulated ponds. Net catfish yield was similar among treatments and averaged 8,385 kg/ha, of which 86% exceeded 0.57 kg average weight. Mean individual weight at harvest among treatments was 0.90 kg. At harvest, fish from all treatments were classified as being off-flavor. Pond circulation impacted positively pond temperature and dissolved oxygen profiles, but did not impact significantly fish production, plankton, or water quality variables.