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The Effect of Fish Farming on Zooplankton Fauna in Kozan Dam Lake

The effect of aquaculture on water quality (Dissolved Oxygen, temperature, pH, conductivity, NO2-N, NO3-N, NH4-N, PO4-P and chlorophyll-a) and zooplankton fauna was investigated in Kozan Dam Lake. As a result of the study, it was determined that fish farming did not have a statistically effect on zooplankton fauna and water quality parameters, but it caused some minor changes. In the study, a total of 50 zooplankton species were identified, including 29 from rotifers, 15 from cladocerans and 6 from copepods and Asplanchna priodonta, Polyarthra dolichoptera, Bosmina longirostris Ceriodaphnia pulchella were found in both stations every month during the study. While the reference station had more species in January, February, March, April, May, June, August, October and November than in the cage station, more species were found in the cage station only in September and November than in the reference station. The annual zooplankton abundance was 3.118±3.927 ind/m 3 at the cage station and 2.552±2.452 ind/m 3 at the reference station. Rotifer species and abundance were higher at the cage station whereas cladocer and copepod species and abundance were higher at the reference station. In the study, the species found only in the cage station were Lecane bulla and Disparalona rostrata while the species found only in the reference station were Cephalodella gibba, Filinia terminalis and Macrothrix laticornis.


Introduction
In order to increase fish production, aquaculture was started in dam lakes with a protocol signed between the General Directorate of Agricultural Production (TÜGEM) and the General Directorate of State Hydraulic Works (DSI) in 1994 [1]. As a result, in Turkey, it was established in trout production farm in a cage in many reservoirs.
Good quality in water is essential in fish production [2]. However, due to daily feed intake and routine processes in fish farm, water quality is significantly affected since nitrate, nitrite, ammonium, phosphate, dissolved substances such as inedible feed, food waste and discharge products are directly released into the environment [3][4][5]. These cause growth disorders in fish, changes in benthos and eutrophication, and they are known to bring many environmental problems such as chemical contamination, changes in physical parameters, and the spread of diseases caused by parasites and fungi [6,7].
Since high density fish is usually stocked in cage fish farm, it is inevitable to use drugs and chemicals for fish health. Some of these are antifungals and antibiotics, copper-containing antifooling dyes, herbicides and phosphate-containing (Trisodium phosphate) disinfectants.
As an important link in the aquatic food web, zooplankton is one of the essential components of all aquatic ecosystems. In addition, some species of zooplankton are used in various studies as water quality, pollution and eutrophication indicator due to their sensitivity to environmental changes [8][9][10][11][12]14] There is a close relationship between the efficiency of the aquatic environment and the diversity and abundance of zooplankton. Zooplanktonic organisms are the main biotic factors of freshwater environments, as they have a significant impact on the growth, survival rate and distribution of fish larvae, as their reproductive periods are short, and their populations grow rapidly and have a renewal feature in a short time.
In this study, the effects of trout production in net cages (600 ton/year) on the water quality and zooplankton fauna were investigated in Kozan Dam Lake. In addition, it is thought that this study will provide data for future water quality, zooplankton and fishing activities.

Materials and Methods
The study was carried out between January 2011 and December 2011 in Kozan Dam Lake, which has 6 km 2 lake area, in Adana province Kozan district (Fig. 1). The dam lake was built between 1967 and 1972 for irrigation purposes. The body volume of the dam, which is the rock body fill type, is 1680000 m³, its height from the river bed is 78.50 m, the lake volume at normal water level is 170.34 hm³, and the lake area at normal water level is 6.42 km². It provides irrigation services on an area of 10220 hectares. In addition, electricity production started in the dam lake in 2010/2011 [15].
Zooplankton samples were taken from 4 stations with horizontal and vertical hauls by using 60 μm mesh size plankton nets on monthly basis for systematic analyses. Zooplankton abundance was determined from the samples taken from first two stations (station 1: cage station and station 2: reference station). On the other hand, samples from the first two stations were used to determine the effect of fish production on zooplankton abundance and diversity. Six litres of water samples were collected from every water depths (surface, 1, 2.5, 5, 10, 15, 20, 30 and 40 m) of first and second stations using Nansen Bottles.
One lt and 0.5 lt of water was used for chlorophyll-a analysis and chemical analysis respectively. The remaining part (4.5 lt) was filtered from a collector having a mesh size of 60 μm and zooplankton was fixed in 4% formaldehyde in 100 cc glass jars. Dissolved oxygen, water temperature, pH and conductivity were measured directly at the field by means of digital instruments (oxygen and temperature: YSI model 52 oxygen meter; pH: YSI 600 pH meter; conductivity: YSI model 30 salinometer). Merck spectroquant Nova 60 spectrophotometer and it's procedure was used to determine NO2-N, NO3-N, NH4-N, PO4-P; the method in APHA 1995 was used to determine chlorophyll-a spectrophotometrically. Secchi Disk depth was measured using a Secchi Disk with a diameter of 20 cm. Species identifications were made using a binocular microscope according to the works of Edmondson [16], Scourfield and Harding [17], Dussart [18], Kiefer and Fryer [19], Koste [20], Negrea [21], Segers [22], De Smet [23,24], Nogrady and Segers [25], Hołynska et al. [26] and Benzie [27].
Zooplankton count was performed using an invert microscope in a petri dish with 2 mm lines at the bottom. The sample cup was made homogenized by shaking and 2 cc sub-sample was taken from the cup and it was placed in a petri dish and the individuals of each species were separately counted. This process has been repeated 4-5 times. SPSS package software was used for statistical analyses (t test).

Results
Although there are differences between the cage station and the reference station in the water quality parameters (Secchi depth, temperature, chlorophyll-a, conductivity, dissolved oxygen, pH, NO2-N, NO3-N, NH4-N and PO4-P) (Fig. 2), there is no statistical difference. The average Secchi Disc depths were very close at both stations, and were determined as 2.74±0.87 at the cage station and 2.75±0.98 at the reference station (Fig. 2).
The temperature was found almost the same at both stations. While the average temperature was 16.78±6.30 °C and 16.67±6.35 °C at the cage station and the reference station respectively.
The temperature was higher at the cage station for 8 months (January, February, March, May, July, August, September, October) and at the reference station for 3 months (April, June, November), and it was equal at both stations in December (Fig. 3B).
It was determined that the temperature increased to a depth of 2.5 m from the surface and decreased from this depth to the bottom. The temperature was higher in the cage station at depths of 1, 5, 10, 15, 20 and 30 m (6 depths), while it was higher in the reference station at 0, 2.5 and 40 m depth (3 depths) (Fig. 4a).
The average chlorophyll-a was 2.97±2.013 mg/m3 at the cage station and 2.99±1.89 mg/m3 at the reference station. While chlorophyll-a was high in the cage station for 5 months (January, March, April, August, November), it was higher in the reference station for 7 months (February, May, June, July, September, October and December). Chlorophyll-a, which increased in spring and autumn in both stations, was close to each other in all months (Fig. 3C)   October and November. It was found that the difference between the two stations was high in March, May and June, and closer to each other in other months (Fig. 3I). The vertical distribution of ammonium nitrogen shows irregular fluctuations in both stations. Ammonium nitrogen was found at 0, 1, 10, 15, 20, 40 m depths at the cage station, whereas it was more at the reference station at 2.5, 5, 30 m depths (Fig. 4h).
The average PO4-P was calculated to be 0.035 ± 0.011 mg/l at the cage station and 0.028±0.012 mg/l at the reference station. PO4-P was high in the cage station during the months of January, February, March, April, June, July, August, September, October, November, but higher in the reference station in May and December (Fig. 3J). While PO4-P showed a depthdependent decrease in both stations, it was higher at all depths in the cage station ( Fig. 4i).
In the study, a total of 50 zooplankton species were identified, including 29 from rotifers, 15 from cladocerans and 6 from copepods (Table 1). Seventeen families were identified from Rotifera and Brachionidae was the most species rich family with 7 species, followed by Collothecidae, Hexarthridae, Lecanidae, Lepadellidae, Synchaetidae and Trichocercidae with 2 species each one. The remaining families from Rotifera were found to contain only one species in each one. Seven families found from Cladocera, Chydoridae was the most species rich family with 6 species, followed by Daphniidae with 4 species and other families were represented only one species each one. Two families were detected from Copepoda, Cyclopidae was the richest family with 5 species, but Ameiridae (Harpacticoida) was represented by only one species.
In the study, the species found only in the cage station were L. bulla and D. rostrata while the species found only in the reference station were C. gibba, F. terminalis and M. laticornis. In addition, the species found mostly in the cage station were A. ovalis, C. pelagica, E. dilatata, K.
cochlearis and L. lunaris, while the species mostly found in the reference station were N. Paracyclops fimbriatus, Nitokra hibernica, and therefore no comment on these species (Table 2). The most species were found at the reference station (23 species) in March, followed by 19 species in September (cage station) and December (referance station). The least species was found in both first two stations in July (5 species) (Fig. 5).
While there were more species in the reference station in January, February, March, April, May, June, August, October, November (9 months), more species were found in the cage station only in September and November (2 months). On the other hand, in July, an equal number of species was found at both stations (Fig. 5).   high at the cage station (5 times) in January, April, August, November and December (Fig. 6).  (Table 3). The abundance of zooplankton species at the cage and reference stations is as in Table 4.

Discussion
Kozan Dam Lake irrigates approximately 10220 ha of agricultural land and generates electricity. The streams feeding the dam are Kırksu and Düzağaç Creek. For this purpose, there is a water flow and mixture in the reservoir, which has continuous water inlet and outlet. This situation causes vertical and horizontal mixing of the reservoir water. Therefore, it was found that there was no significant difference between zooplankton and water quality parameters at different depths of both stations.
The effects of cage fish farming have been analysed by various researchers and it was reported that nitrogen, phosphor and organic material load in sediment were significantly affected by these changes. Researches have shown that negative effects vary according to fish farm capacity, currents, change ratio and total volume of water and the technology used in fish farming [28][29][30].     The effects of cage fish farming have been analysed by various researchers and it was reported that nitrogen, phosphor and organic material load in sediment were significantly affected by these changes. Researches have shown that negative effects vary according to fish farm capacity, currents, change ratio and total volume of water and the technology used in fish farming [28][29][30].
It has been reported that the most common effect of fish farming in lakes leads to a decrease in dissolved oxygen, pH values and Secchi Disk depth and causes an increase in suspended solids, nutrients, electrical conductivity and chlorophyll-a [31][32][33]28]. However, Cornel and Whoriskey [34] reported that pH did not change in the cage station and reference station, and that fish farming did not affect the pH value. In another study at rainbow trout farm, pH and dissolved oxygen did not change significantly between stations, while nutrients (N, P) (excluding nitrite nitrogen) were higher in cage stations similar to those above [35]. Similarly, some other researchers declared that there was no difference between the cage station and reference station in terms of nitrite nitrogen and nitrate nitrogen [29]. Interestingly, Cornel and Whoriskey [34] reported that N and P levels may be the same at the cage station and the reference station in the fish farm that produce below their capacity.
The difference between the two stations in terms of water quality parameters is very small and close to each other and our findings are consistent with the literature findings in the other studies given above. In the study, dissolved oxygen was close to each other at both stations, but it was higher in cold months, especially in the January, November and December reference stations. On the other hand, the vertical distribution of dissolved oxygen was higher at the reference station at all depths.
This shows that fish farming in cage is also in agreement with previous studies, which caused a decrease in dissolved oxygen and Secchi Depth and an increase in nitrogen and phosphate compounds, especially in the places where cages are located.
Some of previous researchers reported that primary productivity increase in cage station due to the nutrients coming from feed and metabolism wastes and this increased the abundance of zooplanktonic organisms [35][36][37]6]. Matsumura-Tundisi and Tundisi [38,39] reported that zooplankton diversity and abundance changed in cage stations due to increased nutrients, phytoplankton, conductivity, bacteria, food item and other factors.
In a study carried out in a tilapia farm, Santos et al., [40] reported only small changes in zooplankton levels. Guo and Li [6] reported that Rotifera was found in small quantity in cage station, however it was more abundant in the station that was outside of the cage. Cladocera was more abundant in the cage station and less abundant in the other station and finally Copepoda abundance was the same in both stations.
In terms of monthly availability, in parallel with the above declarations, Ascomorpha Lecane lunaris was found dominant in cage station. Since the zooplankton found in the reference station are generally large in size, we think that they are consumed by fish that feed on waste feed around the cage, and therefore they are less in the cage station.

Conclusions
Our study is about comparing the effect of fish farming in lakes on water quality and zooplankton in two stations. It was determined that fish farming caused little changes (degradation) in water quality, rotifers were found in the area where they were fish production area, more in terms of species diversity and abundance, and cladocerans and copepods were found more in the area outside the place of fish production area.