|De Regt, Marjan|
Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2000
Publication Date: N/A
Interpretive Summary: Studies were conducted to determine if large fiberglass enclosures could be used in catfish production ponds as an intermediate step between testing compounds that kill algae in the laboratory and testing the same compounds in an entire catfish pond (full-scale). The first study found that mixing of water within the enclosures is necessary to help make conditions more like those in a catfish pond. The second study found that testing compounds that kill algae inside the enclosures is convenient, reliable, and can be used as an intermediate step before testing the compounds in an entire catfish pond.
Technical Abstract: Two studies were conducted to determine the "usefulness" of limnocorrals (in situ enclosures) for evaluating the effects of hytotoxic compounds on phytoplankton community structure and water quality. Limnocorrals consisted of open-bottomed fiberglass cylinders that were 2.44 m in diameter and 1.53 m high. The limnocorrals were placed in an aquaculture pond and allowed to settle 10-20 cm into the bottom mud, forming a watertight seal. The first study evaluated the effect of water mixing on environmental conditions within limnocorrals. Mixing was accomplished by injecting air through diffusers (airstones). Conditions in unmixed limnocorrals rapidly deviated from conditions in the pond, as indicated by a decrease in phytoplankton biomass and an increase in cyanobacteria abundance and soluble reactive phosphorus oncentrations. Conditions in limnocorrals with continuous mixing also deviated from conditions in the pond, but were relatively consistent among replicate enclosures and were stable for at least 2 wk. The second study evaluated the "usefulness" of limnocorrals for testing the effects of phytotoxic compounds on phytoplankton community structure and water quality. A commercial chelated copper algicide was added to randomly selected, mixed limnocorrals at the label-recommended rate. The algicide killed nearly all phytoplankton in the treated enclosures within 1 wk; however, treated limnocorrals were rapidly recolonized by green algae and diatoms. Conditions in untreated limnocorrals remained relatively stable and consistent among replicates for 16 d. Limnocorrals appear to provide a convenient and reliable method for short-term studies of algicides and other water quality manipulations.