Baking yeast is one of the nutrients source for the Chironomus larvae. However, the available literature provides no data on the high doses influence on the development of the culture.

The paper reveals the results of studying the impact of different levels of baking yeast in the nutrient medium without additional aeration on the Chironomus larvae living.

The authors have found a negative impact of baking yeast high doses on the culture. A direct relation was revealed: the higher was the yeast dose the higher was the larvae mortality. All the larvae die in 4–6 days under baking yeast content of 4.4 % in the nutrient medium weight. The larvae live for 7–8 days without additional aeration under the doses of 0.4–3.4 % of baking yeast.

Studying the issues of different types and ages of fish feeding make the basis for fisheries development. Providing fish with the feed containing animal protein is very important nowadays since lack of protein in the fish diets reduces the productivity and causes the feed unjustified overspending and, thus, increases greatly the cost of fish.

Zoobenthos organisms living in water are closely linked to the abiotic factors of water environment, and their number affects the performance of fish.

In recent decades hydrobiologist have actively begun researching the use of chironomids larvae, which are the main component of benthos. Among zoobenthos most efficiently inducing the state of aquatic ecosystems are Chironomids, which constitute about 25 % of aquatic fauna diversity, induce the condition of water fauna biodiversity most efficiently. They are water bioindicators and make the feed object of fish fauna. They play a significant role in the transformation of organic matter in aquatic ecosystems. Chironomus larvae are the representatives of this gender.

Chironomus larva is biologically valuable food and protein source for many fish species off-spring that determines high demand for this type of natural food.

Temperature, substrate nature and texture affect Chironomus larvae development and operation. To increase the content of nitrogen compounds baking yeast is added to the nutrient medium.

According to some studies, the rate of yeast introduced before settling larvae in the culture medium is 100 g per 1 m², and another part of the yeast, 30–40 grams per 1m², is introduced 10–12 days later.

Six groups – a control and five research ones were formed. Each group contained six nutrient media. The nutrient medium was made from native silt selected from the bottom of the Ross River basin in Bila Tserkva town. Every environment was inhabited by 20 larvae Chironomus sized 11–12 mm.

Each medium weighted 0.5 kg. The control group media was not added with the yeast. In the experimental group 1 the culture medium contained 0.4 % of baking yeast. 1.4 and 2.4 % of yeast was added to the experimental groups 2 and 3 the nutrient medium. 3.4 and 4.4 % of yeast were introduced into the nutritional environment of the experimental groups 4 and 5.

Nutrient medium was not aerated. The temperature in the room was maintained at 20 °C. The larvae were counted every three days.

Checking the number of Chironomus larvae reveals that larvae deaths increases 3 days after adding the yeast and increasing the amount of the investigated additive. The number of chironomids living individuals in the experimental group 1 was 51.2 % lower than in the control. The lowest number of live larvae was found in the experimental group 5 nutrient medium where the content of the yeast was 4.4 % of the weight. Using 1.4 %, 2.4 % and 3.4 % of yeast contributed to reduced number of Chironomus by 3.7; 4.5 and 4.1 times respectively.

Continuing the negative effect of high doses of yeast on chironomids on the 6th day of cultivation is revealed. The highest number of live larvae was found in the control. A dose of 0.4 % resulted in 3.7 times decreased number of Chironomus in the nutrient media as compared with the control. 1.4 %, 2.4 % and 3.4 % content of the yeast in the nutrient medium caused the decrease in the number of larvae by 8.27; 16.4 and 33.3 times respectively. Using 4.4 % of yeast caused the death of all the larvae.

Live larvae were found only in the control variant 9 days later and the number of larvae compared with the one counted 6 days later decreased by 5.5 times.

Thus, it has been found that high doses of yeast affects adversely the living activity of Chironomus larvae. Carbon dioxide formation resulted by the yeast action is supposed to be the cause of chironomids death. The death of the larvae in the control can be explained by non-aeration.

Key words: high doses, Chironomus larvae, baking yeast, nutrient medium, the Chironomus larvae survival.