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The effects of selected reference toxicants on embryonic development of the freshwater shrimp Caridina nilotica (Decapoda: Atyidae)

by Ketse, N.

Abstract (Summary)
Aquatic toxicity tests are increasingly being used in water resource management worldwide, and currently in South Africa, policy and legislation are being drafted to reflect this international trend. While standard toxicity test methods and test organisms are being considered to develop and set water quality guidelines and effluent discharge limits, it is not clear whether guidelines and discharge limits set using these standard test organisms will be sufficient to protect South Africa’s scarce water resources. As part of ongoing research to investigate the use of indigenous riverine organisms as toxicity test organisms a number of potential species have been identified, including the freshwater shrimp Caridina nilotica.

For much of the history of aquatic toxicological data the bulk of the data has been generated by acute toxicity testing, based on short exposures and using mortality as the response end point. There are relatively few chronic, longterm tests with sub-lethal endpoints. However, it was recognized that information about longer exposure durations and non lethal response endpoints was needed, instead of mortality. Chronic tests can provide a more environmentally realistic measure of chemical toxicity than acute toxicity tests.

Caridina nilotica has been identified as a potential standard toxicity test organism, as it is widely distributed, easy to find and it occurs in flowing waters. It is an indigenous species which can be easily cultured and maintained in the laboratory and is also ecologically important. Both adults and juveniles have been used successfully in acute toxicity tests at the Institute for Water Research (Rhodes University) and the ability to rear the organisms under laboratory conditions has allowed the development of chronic toxicity tests using C. nilotica. Chronic early life stage tests include continuous exposure of the early life stages, which are presumed to be the most sensitive for aquatic organisms.

This study reports on the embryonic development of C. nilotica at the culture temperature of 24°C. Morphological developmental stages were monitored and measured and 7 developmental stages were identified. Based on the measurements of the features that were identified, toxicity tests using the reference chemicals sodium chloride (NaCl), sodium sulphate (Na[subscript 2]SO[subscript 4]) and cadmium chloride (CdCl[subscript 2]) were undertaken to test the suitability of C. nilotica embryonic development for chronic toxicity tests for use in water resource management. The length, width, length:width ratios and area of the features decreased in size when exposed to the chemicals. The Lowest Observed Effect Concentration (LOEC) values were 2000mg/L for Na[subscript 2]SO[subscript 4], 3000mg/L for NaCl and 0.31mg/L for CdCl[subscript 2]. The No Observed Effect Concentration (NOEC) values were 1000mg/L for Na[subscript 2]SO[subscript 4], 2000mg/L for NaCl and <0.31mg/L for CdCl[subscript 2]. Further research on the teratogenic effects of single chemicals and industrial effluent on developing C. nilotica embryos needs to be undertaken in order to evaluate the described test protocol for use in water resource management.

Bibliographical Information:

Advisor:

School:Rhodes University

School Location:South Africa

Source Type:Master's Thesis

Keywords:institute for water research iwr zoology entomology

ISBN:

Date of Publication:01/01/2007

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