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2018

ISSN 1313 - 8820 (print)ISSN 1314 - 412X (online)

Volume 10, Number 1March 2018

Agriculture and Environment

Influence of biomanipulation on the living communities and the water quality in the Strezhevo hydroecosystem, R. Macedonia

R. Nastova*, V. Kostov, N. Gjorgovska, V. Levkov

Institute of Animal Science, Ss Cyril and Methodius University of Skopje, 1000 Skopje, Republic of Macedonia

(Manuscript received 21 June 2017; accepted for publication 16 January 2018)

Abstract. The aim of this study was to investigate the influence of the biomanipulation on the living communities and water quality in the Strezhevo hydroecosystem, Republic of Macedonia in which a problem with increase of primary organic production has occurred. The biomanipulatory intervention in water bodies is used to prevent the development of macrophyte vegetation. It is achieved by direct influence on the increased development of phytoplanktonic production and macrophytes by gradual and controlled introduction of grass carp (Ctenopharyngodon idella). The study was conducted in the period June-September 2012 in two earthen ponds (A and B), situated in Strezhevo Lake with 100 specimens of grass carp/pond with average individual mass of 4 kg and age of 3–5 years. The following were monitored: water - temperature (°C), pH, dissolved oxygen (O mg/l) and saturation (%); grass carp – length (mm), weight 2

(kg), Fulton and Clark coefficients of fattening, consumption of added in ponds fresh vegetable mass (kg), consisting of Ceratophyllum demersum (hornwort) (95%) and Potamogeton pusillus (small pondweed) (5%). Based on the results obtained, the meliorative ability of this species with high density of the stock was evaluated as very favourable. At optimal temperature, oxygen regime and pH conditions of water, this herbivore fish species consumed the present macrophytic vegetation very intensively, and in the case of its absence, also the additional share of fresh herbal mass, showing certain selectivity towards particular water vegetation species. Thus, grass carp maintains an optimal composition of the macrophytic communities in the hydroecosystem.

Keywords: grass carp, water quality, macrophytic vegetation, phytoplankton

AGRICULTURAL SCIENCE AND TECHNOLOGY, VOL. , No , pp - , 20110 1 57 62 8DOI: 10.15547/ast.2018.01.014

Introduction

Efficiency of biomanipulation with population of fish species in the process of slowing down the quick growth of the primary and a part of the secondary production, as well as of preserving the quality of aquatic ecosystems, has been a subject of vigorous discussions lately. Mesterov et al. (1972) claimed that sanation of shallow lakes and fishponds cannot be completely performed only by using phytophagous fishes, but it is also necessary to mechanically remove the sediment. In the last decades a large number of authors have been analyzing this hypothesis, presenting positive and negative arguments on the potentials of biomanipulation as an anthropogenic intervention for suppressing the enormous development of aquatic macrophytes and the production of plankton in lakes.

Many authors (Budakov and Maletin, 1982; Budakov et al., 1984; Carpenter et al., 1985, 2011; Pujin et al., 1987; Jovanović et al., 1988; Maletin and Kostić, 1988, 1991; Đjukić et al., 1991; Broenmark and Weisner, 1992; Carpenter and Kitchell, 1992; DeMelo et al., 1992; Maletin et al., 1985, 1990, 1994, 1996 and Scholten et al., 2005), point out the importance of fish community in the control of eutrophication and quality of stagnant water and running-water hydroecosystems. The fish community structure was specially analyzed. Their diversity is being enriched with the introduction of allochthonous species in the fish farms and open waters, and its influence on the total ichthyoproduction (Maletin et al., 1986, 1989; Smith and Reay, 1991; Maletin, 1992; Carol et al., 2006).

Implementation of biomanipulation in the fishponds with intensive production process at the same time means planning the density and the diversity of stocked fish based on the biological and economical principles combined with the necessary knowledge of the fishpond production potentials. Besides that, it is also necessary to observe basic abiotic characteristics such as substrate properties, water chemism and hydrological regime (Maletin and Kostić, 1991; Maletin et al., 1996; Uzunova et al., 2015; Dermendzhieva et al., 2018). This means that for high production using combined stock, the quality and the quantity of nutrient resources are not sufficient, but also suitable physico-chemical conditions and technological organization of fishing are necessary (Zhelev et al., 2015). Fish species compositionis is closely related to the following characteristics of the fishponds:

l The amounts of natural feed (phyto- and zooplanktonic communities, macrophytic vegetation, bottom fauna).

l Oxygen supply, as one of the most important factors and an indicator of water quality

l Health condition of the fishes (parasites and contagious diseases).

l Technical conditions and potentials for farming (fishpond size, total increment/ha, capacity and quality of winter shelters, refreshment of the water).

The presence of predator fish species (zander, European catfish, pike) undoubtfully raises the quality and quantity of total production, at the same time providing biological balance and stability of this type of anthropogenic hydroecosystem (Kasprzak et al., 2002; Milošević and Talevski, 2015). Predators reduce the

57

* e-mail: rodne_nastova@yahoo.com

58

density of the populations of certain economically less important fish species which most often arrive into the fisihponds in a passive way, and act as competitors for feed in the process of nutrition of commercial fish species. Besides that, with their growth predator species eliminate specimens in poor condition and ill specimens. In the process of introducing predator species, their age and size compared to those of the non-predator species (carp species, herbivores) must be taken into account. Also, the selection of predator species in obtaining as big as possible diversity of fish communities is directly related to the possibilities for refreshing water in the process of farming. It has to be specifically stressed that fish communities diversity composed in that way offers possibilities for multiple increase of production compared to the monoculture in the conditions when a sufficient amount of feed is provided for the predators. In the opposite case, it may result in cannibalism (Smith and Reay, 1991). Such fish community may enable more complete exploitation of the primary and part of the secondary production and slow down the course of eutrophication, thus maintaining and improving water quality. As a consequence of a complex fish community, an appropriate water quality is maintained which can be evaluated using many standard parameters, both abiotic (dissolved O concentration, saturation, BOD, COD, contents of nutrients – N 2

and P in the first place) and biotic (by analysis of certain members of the living community). Concerning fishes as a component of the hydrobiocenosis which are on the top of the nutrition pyramid, the analyses of the nutrition of certain species, dynamics of growth and fertility, are parameters which can indicate the status and quality of the biocenosis, the habitat and the whole ecosystem (Scholten et al., 2005; Nastova et al., 2014; Dochin and Ivanova, 2015; Velichkova et al., 2017). The present research was performed with the goal of estimating the efficiency of the meliorative effect of grass carp on the control of quantity and diversity of aquatic vegetation in Strezhevo hydroecosystem in the Republic of Macedonia.

Material and methods

Study areaThe study was conducted during the period June-September

2012 with grass carp (Ctenopharyngodon idella), grown in two earthen ponds (A and B) with an area of 0.15 ha each, situated in Strezhevo Lake, Republic of Macedonia. Implanted stock consisted of 100 specimens of grass carp/pond with an average individual mass of 4 kg and age of 3–5 years.

SamplingFor the purpose of the study water samples from both ponds (A

and B) were collected 7 times during the experimental period – twice in June, July and August and once in September (a total of 14 samples).

Parameters and methods for their analysesThe following physico-chemical parameters of the experimental

pond water were determined: temperature (°C) – with a mercury thermometer; pH – electrochemically; dissolved oxygen (O mg/L) – 2

iodometrically according to the Winkler method and saturation (%) by Winkler method (APHA, 2005)

Phytocenologic investigations of water macrophytes were performed according to Braun-Blanquet method.

During the experimental period, natural feed fresh vegetable mass consisting of Ceratophyllum demersum (hornwort) (95%) and

Potamogeton pusillus (small pondweed) (5%), in three equal portions (10 kg in total) per pond was added. The feed consumption (kg) of added fresh biomass was determined in July (30 days) and in August (20 days).

In June, July, August and September the growth in length (mm) and weight (kg), and Fulton and Clark coefficients of fattening of the grass carp (n=100) were determined (Bolger and Connolly, 1989; Ritterbusch-Nauwerck, 1995).

Results and discussion

At the beginning of the experiment, the studied ponds A and B were overgrown with macrophytic vegetation to different extents. In pond A, the dominant species were Typha latifolia (bulrush) and Polygonum lapathifolium, (pale persicaria) and in pond B Phragmites communis (common reed), Typha latifolia (bulrush), Typha angustifolia (lesser bulrush) and Polygonum amphibium (water knotweed). Besides them, Spirodella polyrrhiza (common duckmeat) was present in both ponds. The overall coverage of vegetable layer in pond A was 30–40%, and in pond B over 80%. Specimens of grass carp stocked in these conditions had a total ichthyomass of 400kg. During the month of June it came to decrease in the overall vegetable layer area by some 10%. At the same time, the various overgrowth of macrophytes led to unequal pace of the total fish mass growth (Table 1). After the first two weeks, in pool A the mass of stocked fish was roughly 433kg, and in pond B - 509kg. This difference is above all a consequence of the more abundant food supply in pond B. The coefficient of fattening in this period increased in both fish groups, thus indicating optimal feed supply in the first third of the experiment. In the following months, after the period of adaptation, the nutrition of grass carp became more intensive, which had impact on the total ichthyomass. The overgrowth in both ponds was drastically reduced. In this way, in July macrophytic vegetation in pond A was brought down only to the presence of P. lapathifolium (pale persicaria), while in pond B the overall coverage was 45–50%, with the prevalence of Ph. communis (common reed) and the species from the genus Typha. For this reason, on July the first fresh vegetable mass was added, consisting 95% Ceratophyllum demersum (hornwort) and 5% Potamogeton pusillus (small pondweed), in three equal portions (10kg in total) per pond. In the next days, the supplied amount of additional fresh biomass of aquatic vegetables was being increased, varying according to the consumption.

The consumption of additional phytomass is shown by its daily dynamics (Table 2). In July, in pond A the grass carp consumed 955kg, and in pond B - 435kg of added vegetable mass. This difference between the additional phytomass amounts consumed is a consequence of the different amounts of original nutrients. In this period, the total ichthyomass enhance was significantly increased to 486kg (pond A) and 690kg (pond B). Fattening also increased, especially in the grass carp specimens in pond B. The coefficients of fattening reached their maximum in mid-July.

The situation remained similar in August. In pond A the presence of P. lapathifolium was further registered and the addition of the package Ceratophyllum+Potamogeton continued up to the

th20 of August, with daily controls. The overall coverage in pond B decreased to 35%, with the domination of the same species as in July. By the end of the experiment, the total vegetable mass of macrophytes in pond B was reduced to some 10%, and consisted of Ph. communis and dry samples of T. latifolia and T. angustifolia.

59

Again, higher consumption was registered in pond A (903kg) than in pond B (215kg). However, the total amount of available feed and particularly of the feed originating from the ponds was significantly reduced in both ponds, causing reduction of ichthyomass. The reduction of phytomass causes a decrease in the coefficient of fattening, so the obtained values were similar to the initial ones. With the stoppage of adding fresh mass of water plants and the significant depletion of the vegetation, at the end of the experiment, it came to another drop in the total ichthyomass, and to decrease in fattening as a result of starvation. In the follow-up of the meliorative effect of grass carp in the suppression of the excessive coverage by macrophytic vegetation, special attention was paid to its preferences regarding certain species of macrophytic vegetation. During the whole experiment a permanent presence of the species from the genus Polygonum was registered without any tendency towards

reduction of their quantity and the area covered. Certain selectivity in the nutrition of grass carp under these conditions was found by analysis of the intestine content. The studied specimens shifted to consuming the additional fresh biomass (Ceratophyllum+ Potamogeton) only when the available original vegetation had been depleted, especially the one from the species of Typha genus. The values of water temperature during the whole experiment were ranging 19.3–24.3°C and pH 7.40–9.03. The values for the oxygen regime were mainly satisfactory, but in certain periods some deviations occurred. Extremely high oxygen concentration and saturation were registered at the beginning of the experiment, so their reduction within the normal may be to a great extent attributed to the meliorative role of grass carp. In the experiment, a more significant drop in the amount of oxygen and in oxygen saturation occurred only occasionally, namely – in pond A in September, and in

Table 2. Daily dynamics of consuming additional fresh macrophytic biomass (kg)

Date Date Date DateA A A AB B B B

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Total:

–

–

10

–

–

–

–

–

20

25

–

15

20

50

–

–

–

10

–

–

–

–

–

–

–

–

15

20

–

–

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

30

40

–

30

30

30

50

110

150

110

60

60

–

60

55

955

30

40

–

30

30

50

50

30

–

30

50

–

50

–

–

435

1

2

3

4

5

6

7

8

9

10

Total

55

55

55

55

55

55

58

55

50

55

30

–

35

35

–

–

30

–

20

–

11

12

13

14

15

16

17

18

19

20

55

–

55

50

60

55

45

45

45

45

903

–

30

–

20

–

15

–

30

–

–

215

July August

Ponds Ponds Ponds Ponds

Table 1. Growth in length and weight and coefficient of fattening of grass carp (n=100)

A and B – ponds; M – total ichthyomass (kg/pond); l – individual standard length (mm), Q – Fulton coefficient of fattening; F

Q – Clark coefficient of fatteningC

Date

M Ml lQF QFQC QC

04. June

19. June

01. July

17. July

05. August

19. August

17. September

400

433

430

486

469

452

446

612

617

624

637

638

657

657

1.74

1.84

1.77

1.88

1.80

1.59

1.57

1.57

1.56

1.61

1.67

1.64

1.29

1.41

400

509

550

690

650

620

581

611

641

663

663

682

687

704

1.75

1.93

1.89

2.36

2.05

1.91

1.66

1.59

1.74

1.71

2.01

1.73

1.76

1.50

Ponds

A B

60

pond B - in June (Table 3). The great perspectives of biomanipulation using fishes were

also pointed out by Gophen (1990), mentioning the significant role of grass carp in the transfer of nutrients (mainly P) from sediment through macrophytes. The main limiting factor for successful implementation of this type of biomanipulation are the unfavourable climatic conditions, most of all low temperatures, then the low stocking density, insufficient water quality in winter and other factors (Mueller, 1982; Mihailova and Kostadinova, 2012). The mentioned physico-chemical parameters indicate favourable conditions for implementing biomanipulation by using grass carp in the process of suppression of macrophytic water vegetation. The extremely dense stocking and the relatively old age of the experimental specimens caused quick depletion of the already available and the additionally supplied food, as well as lower growth, thus suggesting the need for using a different combination of the stock in making the plan for solving the problem of suppressing the excessive growth of aquatic weeds. Anyway, such biomanipulation showed itself as the right tool, regardless its positive and negative aspects. Biomanipulation thus represents targeted influencing of lower components of the food chain through fish, as they represent a hierarchically higher component of it (Pípalová, 2006). More appropriately, benthivorous fish have been also included into the subject of biomanipulation efforts as they may contribute considerably to the release of nutrients from bottom sediments due to their disturbance when searching for feed (Adamek and Marsalek, 2013). In the Czech Republic, however, the „controlled fish stock“ is understood by the river authorities in a quite simplified way, just as a regular release of piscivorous species, mostly as a 0+ fish. Thus, as frequently proved, these measures did not bring results as expected. Nevertheless, as a matter of fact, the concentration of phosphorus as a key nutrient driving the development of the primary producers (i.e. cyanobacteria, algae and macrophytes), is usually very high in all Czech reservoirs (Adamek, 2013). Due to excessive intake of phosphorus, the trophic level of surface waters significantly increases causing an undesirable development of planktonic algae and cyanobacteria, which finally results in deterioration of water quality. In many situations, such control of water weeds is a suitable solution and gives satisfactory results compared to some other ways such as mechanical removal, use of herbicides or manipulation with the water level (Rotmann, 1977; Van Zon, 1979). At the same time, previous authors mentioned that regulation of the growth of water vegetation using grass carp is cheaper, nevertheless much longer-lasting than the other methods. An adequate stock of grass carp results in conversion of the unused part of macrophytic production

into edible proteins (Van Zon, 1977). It is necessary to realize that the efficiency of biomanipulation

measures has certain limits that are defined mainly by supply of nutrients (or nutrient load) and morphology (depth) of the reservoir. If the nutrient load of a reservoir exceeds a certain limit, the biomanipulation loses its effectiveness – a significant and long-term reduction of planktonic algae biomass through controlled fish stock is hardly to be expected. Knowledge of the nutrient loading is therefore a necessary prerequisite for deciding on the possibility and suitability of conducting biomanipulation efforts in a concrete water reservoir. An increase of water trophic potential to eutrophy (or even hypertrophy) is usually associated with two main issues - rich deposits of phosphorus in sediments along with a regular occurrence of anoxic conditions in the hypolimnion, and with high loading from external sources (inflow). With respect to deep, thermally stratified reservoirs, this external load should not exceed

2the value of 0.6-0.8g of total phosphorus per m of the reservoir surface per year (Benndorf et al., 2002), if the biomanipulation measures are supposed to show significant improvements of water quality. The limit concentration of total phosphorus in relation to the effectiveness of biomanipulation in deep stratified lakes and reservoirs (average depth of >5-10m) has not been clearly defined by direct scientific studies yet, the limit value corresponding to

-3average annual concentration of total phosphorus of 20-50 mg.m is assumed (Jeppesen and Sammalkorpi, 2002; Mehner et al., 2004).

Conclusion

T h e p r e s e n t s t u d y i n d i c a t e s t h a t g r a s s c a r p (Ctenopharyngodon idella) can be an efficient biomanipulation fish for reducing the macrophytic biomass in Strezevo hydroecosystem. During the first two months of the experimental period (June and July) the total ichthyomass increased (1.21 times in pond A and 1.72 times in pond B), but during the last two months (August and September) its decreasing is noticeable (1.05 and 1.12 times, respectively). A similar tendency was observed in macrophytic biomass consumption. Also, it was noticed that grass carp had different preferences to certain species of macrophytic vegetation. By the introduction and the creation of adequate stock of grass carp, the problem of excessive development of semi-aquatic and aquatic vegetation was successfully solved, getting high-quality proteins of animal origin at the same time. Special attention should be paid to the density and age of fish during planning and implementing the

Table 3. Physico-chemical parameters of water

Date

T°C T°CpH pHO mg/l2 O mg/l2Sat. (%) Sat. (%)

04. June

19. June

01. July

17. July

05. August

19. August

17. September

24.2

21.1

21.3

21.0

24.1

24.1

20.0

8.20

7.50

9.03

7.70

8.42

8.42

7.83

18.6

6.1

10.2

9.7

11.2

11.5

3.6

218

68

114

108

132

135

39

24.3

22.2

21.1

21.1

24.0

24.0

19.3

8.10

7.60

8.37

7.40

8.16

7.85

8.44

19.2

3.5

9.0

6.5

8.6

9.52

7.79

225

40

100

72

101

117

83

Ponds

A B

61

process of suppression of macrophytic water vegetation. Intensive fish breeding in polyculture is an active factor in the process of self-cleansing and maintaining the quality of the entire aquatic ecosystem.

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Dermendzhieva D, Kostadinova G, Petkov G, Nastova R and Dineva I, 2018. Agro-ecological assessment of Sokolitsa River water affected by open coal mining activity in the largest energy complex in Bulgaria. Bulgarian Journal of Agricultural Science, 24 (S 1), in press.Dochin K and Ivanova A, 2015. Study of phytoplankton diversity and hydrochemical regime of Bistrica Dam Lake. Bulgarian Journal of Agricultural Science, 21 (S 1), 137-146.Đukic N, Pujin V, Maletin S, Gajin S, Gantar M, Petrović O, Ratajac R, Selesi D and Matavulj M, 1991. Euthrophication of standing waters of Vojvodina. Part I. Vode Vojvodine, 20, 1-98 (Sr).Gophen M, 1990. Summary of the workshop on perspectives of biomanipulation in inland waters. Hydrobiologia, 191, 315-318.Jeppesen E and Sammalkorpi I, 2002. Lakes. In: Handbook of

Ecological Restoration (Eds. M. Perrow and T. Davy), 2: Restoration practice. Cambridge, Cambridge University Press, pp. 297-324.Jovanović R, Maletin S, Pujin V, Ratajac R, Đukic N and Kostić D, 1988. Meliorative role of herbivores in euthrophic waters. In Proceeding of Conference on current problems of water protection. Water protection '88, Dojran. Zbornik radova, 700-706 (Sr).Kasprzak P, Benndorf J, Mehner T and Koschel R, 2002. Biomanipulation of lake ecosystems: an introduction. Freshwater Biology, 47, 2277-2281. Maletin S, Budakov LJ and Kostić D, 1985. The growth of silver carass as a water quality assessment. Yearbook on current problems of water protection. Zaštita voda, 1, 94-97 (Sr).Maletin S, Đukic N and Kostić D, 1986. Fish production in some reservoirs of Vojvodina. In Proceedings of Conference on current problems of water protection. Water protection, Kragujevac, 144-151 (Sr).Maletin S and Kostić D, 1988. The role of gray tolstolobics in the protection of the water quality of Ludos lake. In: Proceedings of Conference on current problems of water protection. Water protection, Dojran, pp. 93-99 (Sr).Maletin S, Đukic N and Kostić D, 1989. The significance of fish settlements in the process of self-purification of watercourses. In: Proceedings of Protection of waters `89, Rovinj, Book 1, pp. 487–494 (Sr).Maletin S, Pujin V and Đukic N, 1990. Fish growth as an indicator of some stagnant waters eutrophication rate in Vojvodina. Archives of Biological Science, 42, 237-246.Maletin S and Kostić D, 1991. Lanngenwuchs der allochtonen pflanzenfresser in einzelnen donauabschnitten in der Vojvodina. Limnologische Berichte der 29. Tagung der IAD, Wissenschaftliche Kurzreferate, Kiew, UdSSR, pp. 232-236. Maletin S, 1992. Exploration state of allochthonous fish fauna in Vojvodina. Ichthyologia, 24, 19-24.Maletin S, Đukic N, Stojanović S, Ivanc A, Žderić M, Matić A, Andrić A, Radak LJ and Miljanović B, 1994. Meliorative effect of gras carp (Ctenopharyngodon idella) in controlling aquatic macrophytes in the Tiszavalley. Tiscia, 28, 41-45.Maletin S, Đukic N, Pujin V, Miljanović B and Ivanc A, 1996. Application of physicochemical and hydrobiological methods in the unique assessment of surface water quality. In: Proceedings Protection of water, Ulcinj, pp. 288-291 (Sr).Mehner T, Arlinghaus R, Berg S, Dörner H, Jacobsen L, Kasprzak P, Koschel R, Schulze T, Skov C, Wolter C and Wysujack K, 2004. How to link biomanipulation and sustainable fisheries management: a step-by-step guideline for lakes of the European temperate zone. Fisheries Management and Ecology, 11, 261-275. Mesterov M, Ilijanić LJ, Tavćar V and Koprek J, 1972. The influence of the white amur population (Ctenopharyngodon idella Vall.) On vegetation and ecosystem of Tracoshchann Lake. Acta Botanica Croatica, 32, 125-134 (Sr).Milošević D and Talevski T, 2015. Conservation status of native species in natural lakes of Drim system (Prespa, Ohrid and Skadar Lake) and dangers of commercial fishing. Bulgarian Journal of Agricultural Science, 21 (S 1), 61-67.Mihailova G and Kostadinova G, 2012. Macrozoobenthos communities as indicator for ecological status assessment of surface water bodies in Toundja River, Bulgaria. Journal of Balkan Ecology, 15, 173-190. Mueller R, 1982. Grass carp and silver carp in Switzerland. In Proceeding of IV European Congress of Ichthyology, p. 207.

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Review

Achievements and problems in the weed control in grain maize (Zea mays L.)G. Delchev, M. Georgiev

Genetics and Breeding

Yield and coefficient of ecological valence of spring barley in the regions of Sadovo and Karnobat, BulgariaN. Neykov, T. Mokreva

Agronomic performance of mutant lines of winter two-rowed barleyB. Dyulgerova, D. Valcheva, N. Dyulgerov

Phenotypic diversity in six-rowed winter barley (Hordeum sativum L.) varietiesN. Dyulgerov, B. Dyulgerova

Evaluation of rye specimens in maturity stage on the base of mathematical – statistical analysisV. Kuneva, E. Valchinova, A. Stoyanova

Evaluation of lentil cultivars and lines for resistance to Fusarium oxysporum f.sp. lentisM. Koleva, Y. Stanoeva, I. Kiryakov, A. Ivanova, P. Chamurlyiski

Registration of a new sunflower hybrid - SevarP. Peevska, M. Drumeva, G. Georgiev

Nutrition and Physiology

The effect of novel xylanase on feeding value of diet containing cereal by-products for broilersJ.M. Abdulla, S.P. Rose, V. Pirgozliev

Effect of dietary garlic powder and probiotics supplementation on growth performance of male Ross 308 broilersH. Lukanov, I. Pavlova, A. Genchev

Slaughter traits of Pharaoh Japanese quails А. Genchev, H. Lukanov, I. Penchev

Blood count in dogs with mammary gland carcinomaTs. Hristov, R. Binev

Production Systems

Economic efficiency of fattening on different genotypes slow-growing and fast-growing broiler chickens M. Oblakova, Y. Popova, P. Hristakieva, N. Mincheva, M. Lalev

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Effect of nutmeg extract supplementation on some productive traits and economic efficiency of common carp (Cyprinus carpio L.) cultivated in recirculation system G. Zhelyazkov, S. Stoyanova, I. Sirakov, K. Velichkova, Y. Staykov

Agriculture and Environment

Influence of biomanipulation on the living communities and the water quality in the Strezhevo hydroecosystem, R. MacedoniaR. Nastova, V. Kostov, N. Gjorgovska, V. Levkov

Product Quality and Safety

Residue analysis of difenoconazole in apple fruits grown in Republic of MacedoniaV. Jankuloska, I. Karov, G. Pavlovska

Organoleptic properties of white yam (Dioscorea rotundata poir) as affected by autoclaving timeM. Ahmed, Y.B. Kiri, M.S. Abubakar

Influence of Goji berries on oxidative changes, microbiological status and chemical properties of sausagesA. Mitev, A. Kuzelov, E. Joshevska

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Instruction for authors

Preparation of papersPapers shall be submitted at the editorial office typed on standard typing pages (A4, 30 lines per page, 62 characters per line). The editors recommend up to 15 pages for full research paper ( including abstract references, tables, figures and other appendices)The manuscript should be structured as follows: Title, Names of authors and affiliation address, Abstract, List of keywords, Introduction, Material and methods,Results, Discussion, Conclusion, Acknowledgements (if any), References, Tables, Figures.The title needs to be as concise and informative about the nature of research. It should be written with small letter /bold, 14/ without any abbreviations. Names and affiliation of authorsThe names of the authors should be presented from the initials of first names followed by the family names. The complete address and name of the institution should be stated next. The affiliation of authors are designated by different signs. For the author who is going to be corresponding by the editorial board and readers, an E-mail address and telephone number should be presented as footnote on the first page. Corresponding author is indicated with *.Abstract should be not more than 350 words. It should be clearly stated what new findings have been made in the course of research. Abbreviations and references to authors are inadmissible in the summary. It should be understandable without having read the paper and should be in one paragraph. Keywords: Up to maximum of 5 keywords should be selected not repeating the title but giving the essence of study. The introduction must answer the following questions: What is known and what is new on the studied issue? What necessitated the research problem, described in the paper? What is your hypothesis and goal ?Material and methods: The objects of research, organization of experiments, chemical analyses, statistical and other methods and conditions applied for the experiments should be described in detail. A criterion of sufficient information is to be possible for others to repeat the experi-ment in order to verify results.Results are presented in understandable

tables and figures, accompanied by the statistical parameters needed for the evaluation. Data from tables and figures should not be repeated in the text.Tables should be as simple and as few as possible. Each table should have its own explanatory title and to be typed on a separate page. They should be outside the main body of the text and an indication should be given where it should be inserted.Figures should be sharp with good contrast and rendition. Graphic materials should be preferred. Photographs to be appropriate for printing. Illustrations are supplied in colour as an exception after special agreement with the editorial board and possible payment of extra costs. The figures are to be each in a single file and their location should be given within the text. Discussion: The objective of this section is to indicate the scientific significance of the study. By comparing the results and conclusions of other scientists the contribution of the study for expanding or modifying existing knowledge is pointed out clearly and convincingly to the reader.Conclusion: The most important conse- quences for the science and practice resulting from the conducted research should be summarized in a few sentences. The conclusions shouldn't be numbered and no new paragraphs be used. Contributions are the core of conclusions. References:In the text, references should be cited as follows: single author: Sandberg (2002); two authors: Andersson and Georges (2004); more than two authors: Andersson et al.(2003). When several references are cited simultaneously, they should be ranked by chronological order e.g.: (Sandberg, 2002; Andersson et al., 2003; Andersson and Georges, 2004).References are arranged alphabetically by the name of the first author. If an author is cited more than once, first his individual publications are given ranked by year, then come publications with one co-author, two co-authors, etc. The names of authors, article and journal titles in the Cyrillic or alphabet different from Latin, should be transliterated into Latin and article titles should be translated into English. The original language of articles and books translated into English is indicated in parenthesis after the bibliographic reference (Bulgarian = Bg, Russian = Ru, Serbian = Sr, if in the Cyrillic, Mongolian =

Мо, Greek = Gr, Georgian = Geor., Japanese = Jа, Chinese = Ch, Arabic = Аr, etc.)The following order in the reference list is recommended:Journal articles: Author(s) surname and initials, year. Title. Full title of the journal, volume, pages. Example:Simm G, Lewis RM, Grundy B and Dingwall WS, 2002. Responses to selection for lean growth in sheep. Animal Science, 74, 39-50Books: Author(s) surname and initials, year. Title. Edition, name of publisher, place of publication. Example: Oldenbroek JK, 1999. Genebanks and the conservation of farm animal genetic resources, Second edition. DLO Institute f o r A n i m a l S c i e n c e a n d H e a l t h , Netherlands.Book chapter or conference proceedings: Author(s) surname and initials, year. Title. In: Title of the book or of the proceedings followed by the editor(s), volume, pages. Name of publisher, place of publication. Example: Mauff G, Pulverer G, Operkuch W, Hummel K and Hidden C, 1995. C3-variants and diverse phenotypes of unconverted and converted C3. In: Provides of the Biological Fluids (ed. H. Peters), vol. 22, 143-165, Pergamon Press. Oxford, UK.Todorov N and Mitev J, 1995. Effect of level of feeding during dry period, and body condition score on reproductive perfor-

thmance in dairy cows,IX International Conference on Production Diseases in Farm Animals, September 11–14, Berlin, Germany.Thesis:Hristova D, 2013. Investigation on genetic diversity in local sheep breeds using DNA markers. Thesis for PhD, Trakia University, Stara Zagora, Bulgaria, (Bg).

The Editorial Board of the Journal is not responsible for incorrect quotes of reference sources and the relevant violations of copyrights.

Animal welfareStudies performed on experimental animals should be carried out according to internationally recognized guidelines for animal welfare. That should be clearly described in the respective section “Material and methods”.

Volume 10, Number 1March 2018

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