180 



A convenient dredge is the light portable dredge with a curved oval frame 

 named Dorogostaiskii's dredge (Figure 173). This works well on stone, 

 sand- stone or gravel bottoms of rivers or in the open littoral of lakes; 

 it may be used on sand bottoms in the sub littoral zone of lakes. A 

 convenient trawl is the small Sigsby trawl (Figure 174). Bottom-samplers 

 (Echmann-Berge, Petersen and their modifications) are used for work on 

 loose sand bottoms. 



Examination of the fauna of stones is made with other instruments, e. g., 

 Gerd's frame (Gerd, 1951:136; Zhadin, 1956:289). This is a square frame 

 (25 X 25 cm) of galvanized iron with 15 cm-high walls with pointed legs 

 5—10 cm high. If shallow water with a bottom of pebbles or small stones is 

 examined, the frame is put on the bottom, and its legs are pushed into the 

 sand or rubble under the stones; the stones are taken from the frame; the 

 animals floating or falling from the stones are collected with a small net 

 about 15 cm wide. Caddis fly larvae usually cling to the stones; The 

 specimens are then counted and weighed; the number of specimens and 

 their biomass are related to the bottom surface covered by the frame; 

 these figures are usually calculated for 1 m . The caddis fly population of 

 stony water bottoms is often dense; for example, in some biotopes in Lake 

 Onega, there were up to 289 specimens per m with a biomass of 3.1 g/m 

 (a biomass of 31 kg/hectare). 

 181 Work in mountain brooks with a bottom covered with boulders and 

 pebbles and with a rapid current (l. 8— 2 m/ sec) is done with Sadovskii's 

 behthometer; this functions in the current (Sadovskii, 1948:366, Figures A— C; 

 Zhadin, 1956:290). It consists of a metal cylinder open at top and bottom 

 75 cm high, with a serrated lower margin and 2 handles at the upper margin; 

 at 1 side of the cylinder there is a square "window" covered with a metal 

 screen (38 X 38 cm); on the other side is an opening of the same size, to 

 which a metal frame with a canvas bag is connected. The benthometer is 

 used as follows: it is pressed into the bottom; the pebbles and gravel in 

 the benthometer are stirred through the open upper part; the stones are 

 then taken out and the organisms washed from them are carried by current 

 into the canvas bag; they are then counted. If quantitative collections of 

 caddis flies are made, the larvae are taken from the cases and dried with 

 filter paper; after the material has been weighed, the case is put back on the 

 larvae if they are to be preserved. The larvae are preserved in their 

 cases, which are an important character of the species; it is often impossible 

 to identify the larvae without the case. Quantitative methods are recom- 

 mended, as Trichoptera are an important part of the food of fish. 



Larvae and pupae should be preserved in 80—90° alcohol; this has to be 

 changed if it becomes yellow or green from the plant particles of the case. 

 Egg masses of caddis flies should be placed in 4% formaldehyde in which 

 they preserve their form, and to some extent, their color; the egg masses 

 shrink rapidly and lose their form in alcohol. 



Not all larvae and pupae of Trichoptera in the USSR are known, and 

 collection of all stages of the larvae is, therefore, valuable. 



In order to identify the species of a new larva some specimens should 

 be kept alive until they pupate; it is then possible to identify the adults 

 hatching from the pupae. 



Caddis fly larvae in stagnant water live well and complete their 

 development in an aquarium with sufficient food and oxygen. After the 



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