I.A.Chemerys, L.L.Bilyk, S.F.Zrazhevsky, V.S.Sych

Cherkasy State Technological University

Modern situation of roach in Kremenchug reservoir and its industrial use

The load on natural and antropogenic systems surpasses their possibilities for self renewal and is leading to gradual degradation of biotic complex both in regional and global scale. In conditions of uncontrolled growth of population (FAO data –food and agricultural UNO organization) about 1.5 bn people in the world suffer of under-nourishment and starvation. It is predicted that in 2010 the number of people on Earth will exceed 7 billion at the same level of deficiency of food products. Fish industry has great potential in food provision of the population and Ukraine has quite enough available fish-producing water reservoirs which can provide the population with food products.

Reservoirs of Dnieper cascade are referred to ecosystems having great national importance.

Kremenchug water reservoir is one of the most productive in the Dnieper cascade. Its ichtiofauna numbers 41 species of fish among which 17 kinds have industrial importance including large-mesh fish: abramis-bream, Chinese carpide, cat fish, pike, grass carp, pike-perch, asp, ide; fine-mesh fish; European roach, bream, zope, perch, Prussian carp, sabre fish, perched, sprat. Species composition of fish was formed mainly at the expense of those species which populated the Dnieper and its additional systems till the reservoir was formed. The most important are those species which had the greatest initial shoal and the best conditions for spawning.

Formation of shoals of abramis-bream, wild carp and pike-pearch was greatly influenced by measures taken before the formation of water reservoir: whole-year prohibition for fishing out five years before filling the reservoir, increased fishing of small-value and weed fish by introducing temporary rules of fishing from the first year of water reservoir existence; prohibition of fishing out in mouths of water reservoir tributaries –Vilshanka, Tsybulnik, Sula: organization of breeding points on the Ros and the Vilshanka for the production and installation of artificial nests for spawning of valuable kinds of fish. Chinese carpide is a valuable introducent of Kremenchug water reservoir, its introduction started after the creation of warer reservoir.

The reason of rapid decrease of stock of the main industrial kinds of fish and degradation of ichtiofauna quality was deterioration of conditions for fish growth, uncontrollable fishing out of the most valuable species of fish during the period of spawning migration and spawning, construction of hydroelectric stations and usage of water for industrial and agricultural purposes.

Small-value kinds of fish started taking the main place in fishing such as Prussian carp, rudd, perched, oxtongue, pseudorasbora. As a result volume of fishing of such valuable industrial species as abramis-bream, pike-perch, cat-fish was gradually decreased and some of them took secondary place in fishing in this water reservoir.

The main industrial kinds of fish at present are European roach, abramis bream, pike-perch, sabre fish, Prussian carp, bream, zope and plant-fish.

The part of the basic industrial kinds of fish in the general fishing in 2013 shows that European roach, abramis-bream and plant-fish predominate in biodiversification of ichtiofauna of Kremenchug water reservoir. Part of predatory fish was the highest in the fishing of 1970-1980 of tha last century during the period of flourishing of water reservoir productivity. At present part of fishing out of predatory kinds of fish in general fishing fluctuates in between 0.1% (pike) to 1.6% (pike-perch) (table 1).

Table 1. - Main industrial kinds of fish in Kremenchug reservoir.

Kinds of fish	Catch, t	Part of caught industrial fish from general catch, %
European roach	1479,51	34,6
Abramis-bream	1767,97	41,3
Pike-perch	70,24	1,6
Prussian carp	60,86	1,4
Bream	302,35	7,1

Despite the rapid decrease of the stock of the most valuable industrial fish of Kremenchug water reservoir some kinds of fish live in this reservoir, did not lose its numbers and at present even began to renew the population. The growth of the numbers of these species leads to the formation within their population of a considerable number of local groups differing in the tempo of their growth, time of reaching sexual maturity and other biological indices. In connection with this problem and taking into consideration potential possibilities of using various groups for fishing it is important to determine the main biological parameters of this shoal for further evaluation of the stock.

One of such kind is European roach Rutilus rutilus which alongside with abramis –bream is the main industrial fish of this water reservoir. Systematiclly Rutilus rutilus is a typical species of Rutilus which along theareal creates some sub-species and local groups.

In Ukraine time of reproduction of Rutilis rutilus from different water reservoirs and even different parts of the same water reservoir is somewhat different. Mass spawning during the last ten years happened during the last decade of April, except the year of 2005 (the second decade of April) and water temperature in the places of control nets measured at the depth of 1 meter fluctuated at the beginning of spawning within 9.0—12.8 C, at the end of spawning within 13.0—18,0 C.

Lately we are watching the decrease of the number of young riverside low-value species of fish (Prussian carp, rudd, perched, oxtongue, pseudorasbora and others) as a result of which fodder supply of this water reservoir is more completely used by other types of fish. The growth of a number of young industrial species of fish testifies to this.

In spawning European roach population, which was under analysis, present were 18 age groups from two-year -old roach to 19-year-old ones. In both sex groups there were more two and three year old roaches, general volume of females was 55.8% and males 57.3% from the general number of sampled population.

Fish of younger and older age groups were represented in the general volume by considerably lower relative number; there were 6.1% females and 18.4% males for two -year -old fish and 38,1% females and 24.3% males for five-year-old and older fish.

At the same time rather large number of three-year-old and four-year-old fish in the part of the population which was analyzed indicated at insufficient pressure of fishing on this species.

Table 2.- Sex structure of spawning shoal of European roach

Age group	Sex structure				Correlation of sexes
	Males		Females
	Specimen	%	Specimen	%
1	2	3	4	5	6
2	113	18,2	44	6,1	1,0 : 0,39
3	194	31,2	223	30,8	1,0 : 0,87
4	160	25,7	181	25,0	1,0 : 0,88
5	74	12,0	49	6,8	1,0 : 1,51
6	11	1,8	27	3,7	1,0 : 0,41
7	15	2,4	44	6,1	1,0 : 0,34
8	10	1,6	27	3,7	1,0 : 0,37
9	9	1,5	35	4,8	1,0 : 0,26
10	8	1,3	34	4,7	1,0 : 0,24
11	4	0,6	17	2,3	1,0 : 0,23
12	13	2,1	30	4,1	1,0 : 0,43
13	4	0,6	12	1,6	1,0 : 0,33
14	3	0,5	-	-	-
15	1	0,1	-	-	-
16	1	0,1	-	-	-
17	1	0,1	-	-	-
18	1	0,1	-	-	-
19	1	0,1	-	-	-
Total	622	46,24	723	53,7	1,0 : 0,86

The number of males in the spawning population of the investigated European roach was significantly larger only in younger age groups (30.8—25.0%), in older age groups their relative weight was rather lower than the number of females and the remaining age groups were represented by only females. The largest number of males were observed among five-year-olds which is characteristic for this species in general and for definite shoal taken separately. Correlation of sexes in this age group was 1.0 : 1.51.

As a result of the enumerated factors there emerged a critical situation of the renewal of fish stock in Kremenchug water reservoir and it is necessary to use measures for urgent renewal of fish stock in Kremenchug water reservoir. Timely clearing and deepening of ways of gonads to the places of spawning and migration of young fish to the places of fattening can make provisions for the higher level of natural renewal of the main species of industrial fish and productivity of Kremenchug water reservoir. That is why Charkasy regional administration with the participation of representatives of ecological safety and local self-administration regularly inspect all problematic shoal-water of Kremenchug water reservoir and analyze in detail all changes which happened during the last years. It is impossible to carry out all the melioration work to deepen the bed on shoal-water of Kremenchug water reservoir as regional fund for protecting nature does not have enough money, the state does not allocate funds for the solution of this problem.

Activity of fish farms in Cherkasy region during the latest years was directed first of all at decreasing the number of low-value and weed fish and considerable increase of valuable industrial species. Fish farms of Cherkasy region and the neighboring Poltava region carry out a lot of work to renew fish stock and look after the water area of the water reservoir. They grow young fishes fresh from the spawn of the most valuable species of fish, clean channels from silting, elaborate measures directed at decreasing fish mortality, clean reservoir bed from garbage and lost fish nets.

This water reservoir is getting “older” starting from the 90s and up to now as a result of termination of melioration work which results in silting and overgrowth of shoal-water with algae. In such conditions the population of abramis-bream is gradually renewed. Further “ageing” of the water reservoir resulted in the increase of Prussian carp and bream population. These species are undemanding to the quality of water. We can state that the worse the conditions in the reservoir the better Prussian carp feels and very quickly breeds in silted and overgrown water reservoirs.

Yearly excessive variation of the water level of the Kremenchug water reservoir from November through May during the period of wintering and spawning is problematic for protecting and renewal of live aquatic resources. It is necessary to keep the level of the water reservoir from November till March corresponding to the requirements of these species spawning to prevent fish mortality and provide optimum conditions for early-spawning fish (pike, pike-perch and others). This is the condition for the gradual renewal of biodiversity of ichtiofauna of the Kremenchug water reservoir.