Fragile mayfly
Ametropus fragilis Albarda, 1878
Order Mayflies (Ephemeroptera)
Family Sand minnow mayflies (Ametropodidae)
Conservation status: in Bulgaria: Extinct EX.
General distribution. The Netherlands, Estonia, Lithuania, Poland, the Czech Republic, Slovakia, Northeastern Italy, Hungary, Romania, Northern Bulgaria, the Ukraine and Northern Asia to the Far East (the rivers Ural, Ob and Amur).
Distribution and abundance in Bulgaria. Only known from the Danube. The species has been reported near Lom and Ruse between 1954 and 1964, most often with few specimens [1, 2]. It has not been found since 1973 in the Bulgarian section of the Danube [3, 4].
Habitats. A psammophilous species inhabiting rivers with sandy bottoms or sand mixed with small quantities of detritus, as well as sand-clay or sand-gravel substrate covered with a thin layer of dead organic matter (fallen leaves) [5]. The nymph lives in the middle and the lower courses of lowland rivers (up to altitudes of 200 m) [6]. It prefers strong currents [7], beta-mesosaprobic water and a depth of 1-2 m [8, 9] but it has also been found at larger depths, up to 9 m [7].
Biology. The nymph is of the swimming type, with a small head. It buries itself quickly into the sand with the help of its large and long claws of the forelegs. It feeds on dead organic matter (detritus) [5, 10]. The species has one generation yearly. After egg hatching, there follows a fast development of the nymphs until the end of the autumn and their slow maturing in the winter. The adult emerges in the spring of the following year (in May and the beginning of June). Before the metamorphosis the nymph goes out of the sand and swims onto the surface. The subimago lives for 24 hours and the adult up to 2-3 days [5]. After the mating, the females lay eggs on the water surface.
Negative factors. The main threats for the species are degradation of habitats, the water pollution of the Danube and of its large tributaries in Bulgarian section.
Conservation measures taken. None.
References. 1. Russev, 1959; 2. Russev & Vidinova, 1994; 3. Russev & Uzunov, 1991a; 4. Russev & Uzunov, 1991b; 5. Jazdzewska, 1973; 6. Landa & Soldan, 1985; 7. Russev, 1968; 8. Keffermuller, 1959; 9. Soldan, 1992; 10. Kazlauskas, 1962.
Author: Yanka Vidinova
