A chronic toxicity test protocol using Caridina nilotica (Decapoda: Atyidae) and the generation of salinity toxicity data

Abstract

Salinization of freshwater resources is an increasing global problem, yet there is a paucity of chronic salinity tolerance data linked to very few chronic toxicity test protocols. This research aimed to generate a chronic toxicity test protocol and protective salinity tolerance data for the indigenous South African freshwater shrimp Caridina nilotica. In addition, the theory that LC₅s (concentration causing 5% lethality) are indicative of No Observed Effect Concentrations (NOECs) was tested. NaCl and Na₂SO₄ were used as toxicants as they are indicative of natural and industrial salinization, respectively. NOEC values of 1.9 g l^–1 were calculated for both salts. Within the chronic toxicity tests, LC₅s that were calculated using regression methods approximated the calculated NOEC values for both salts. Chronic NOECs calculated here are lower, by a factor of 3, than the acute LC₅₀s calculated for the same species and salts. Although evidence exists to suggest that C. nilotica is generally sensitive to toxicants, it was found to be not particularly sensitive to salinity. However, the species was found to be a good chronic toxicity test organism for partial life-cycle toxicity tests where growth was measured as the test endpoint, and may yield valuable chronic toxicity data for other toxicants.