Two different quantities of rations (80 and 160 mg Tetramin® flakes) were compared, combined or not with a weekly renewal of the overlying water. The behaviour of the worms that escaped from sediment resulted in a reduction of their feeding activity, reproduction, and also mortality during the chronic test. The presence of ammonia at toxic levels in the artificial sediment during the first days after its preparation influences the quality of the water column and interstitial water, affecting the biological results of the test. The addition of supplementary food to the sediment at the beginning of the test is necessary to get satisfactory reproductive levels at the end of the 28-day chronic test, but this supplement of organic matter also provoked an additional increase of the levels of ammonia.

In the present study, artificial sediment has been used with Tubifex tubifex (Tubificidae, Oligochaeta) in both culture and in 28-day toxicity tests with spiked toxicants, in order to avoid the presence of occasionally important concentrations of some pollutants in sediments from apparently clean sites. Wolf K, Markiw ME, Hiltunen JK (1986) Salmonid whirling disease: Tubifex tubifex (Muller) identified as the essential oligochaete in the protozoan life cycle.'The formulation and preparation of artificial sediments to be used in chronic toxicity tests is an important issue in the standardisation process. Wolf K, Markiw HE (1984) Biology contravenes taxonomy in the Myxozoa: new discoveries show alternation of invertebrate and vertebrate hosts. Markiw ME, Wolf K (1983) Myxosoma cerebralis (Myxozoa, Myxosporea) etiologic agent of salmonid whirling disease requires tubificid worms (Annelida: Oligochaeta) in its life cycle.

Levine ND, Corliss JO, Cox FEG, Deroux G, Grain J, Honigberg BM, Leedale GF, Loeblich AR, Lóm J, Lynn D, Merinfeld EG, Page FC, Polyansky G, Sprague N, Navra J, Wallace FG (1980) A newly revised classification of the Protozoa. Hoffman G (1962) Whirling disease of trout. Hamilton AJ, Canning EU (1987) Studies on the proposed role of Tubifex tubifex (Muller) as an intermediate host in the life cycle of Myxosoma cerebralis Hofer, 1903. El-Matbouli M, Hoffmann R (1987) Eine neue Myxobolus-Art (Myxozoa Myxobolidae) im Zentralnervensystem der Koppe ( Cottus gobio).

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