Research Product

For several years, researchers at the Gulf Breeze Environmental Research Laboratory have been refining techniques for the flow-through bioassay, a testing method in which a continuous supply of natural seawater flows through experimental tanks. The flow-through bioassay offers many advantages over static exposure methods. Continuously flowing seawater simulates more closely the natural estuarine or marine environment, substantially reducing problems associated with static methods such as poor mixing of toxicants, death of experimental animals from anoxia, adsorption of toxicant to sediments and to walls of exposure tanks, and excess growth of microorganisms. Temperature and salinity affect bioassays. For example, in a freshwater study, the combination of the pesticide dieldrin and thermal changes reduced survival of the darter, Etheostoma nigrum. Temperature and salinity stress increased mortality in fiddler crabs, Uca pugilator, exposed to mercury. Similarly, pink shrimp, Penaeus duorarum, previously exposed to sublethal concentrations of the polychlorinated biphenyl AroclorŪ 1254, died when the salinity was gradually lowered from 20 o/oo to approximately 12 o/oo. If results of toxicity tests are to be confirmed, identical test conditions must be repeated. It is important, therefore, to control temperature and salinity in a flow-through bioassay. Finally, the ability to control temperature and salinity facilitates studies of toxicant and environmental stress interactions. Our flow-through system has been used extensively in bioassays with the pink shrimp, Penaeus duorarum, as well as grass shrimp, Palaemonetes vulgaris and P. pugio. The pink shrimp is a valuable commercial species and both pink and grass shrimp are integral parts of both estuarine and marine food webs. Although the method described here deals with shrimp, this flow-through bioassay method, with minor modifications, is readily adaptable to a wide variety of estuarine and marine macroinvertebrates. The cost of this system for a laboratory with flowing seawater would be approximately $1,500, an amount within the means of many research budgets.