Reproduction Properties of Wels Catfish (Silurus glanis, L., 1758) Inhabiting Sıddıklı Reservoir

In this study, some reproduction properties (sex ratio, reproduction period, egg diameter and fecundity) of Silurus glanis inhabiting Sıddıklı Reservoir were investigated. A total of 200 samples were caught between September 2015 and August 2016 from different regions of Sıddıklı Reservoir. Sex ratio was calculated as 0.88:1.00 (Female: Male). The sex ratio was not statistically different from the expected 1.00:1.00 (χ2= 0.841, P>0.05). The values of gonadosomatic index (GSI) varied from 0.033 to 11.80 in females and 0.008 to 0.451 in males. According to GSI values, reproduction period of the S. glanis in Sıddıklı Reservoir was determined to be between April and June. The mean total fecundity and egg diameter were calculated as 46343 eggs/individual and 1.758 mm, respectively. Relative fecundity for each kilogram of female fish was 13000 eggs. The strong relationships between total fecundity-length and total fecundityweight were determined (r>0.80).


Introduction
The population characteristics of fish, especially reproduction information, are very important data in the evaluation and management of fish stocks (Froese 2004). The data such as sex ratio, length of first sexual maturity, maturation cycle and spawning period are the main parameters of reproduction biology studies (Reddy 1979). To understand the physiology of the fish reproduction, seasonal and developmental changes of the gonads need to be examined with macroscopic and microscopic observations (Priyadharsini et al. 2013). Gonadal development and reproduction season form the basis for future work on the breeding frequency of the population (Chakraborty et al. 2007).
Silurus glanis L., 1758 is a species of fish that is consumed by people and has high economic value. Many countries have been cultivating for many years (Linhart et al. 2002). S. glanis inhabits in slowflowing, large and medium-sized rivers, lakes with stagnant water deposits and intense vegetation (Kottelat and Freyhof 2007). The S. glanis entered Turkey through the Trakya region and showed the distribution in the Marmara, Southeastern Anatolia, Aegean, Mediterranean, Black Sea and Central Anatolia regions (Geldiay and Balık 2007;Polat and Uğurlu 2011).
In Turkey, there have been a few studies about the reproductive biology of S. glanis (Akyurt 1988;Alp et al. 2004). Therefore, in this study, it is aimed to reveal some reproductive characteristics of S. glanis inhabiting Sıddıklı Reservoir.

Study Area
Sıddıklı Reservoir located near Sıddıklı Küçükboğaz Village, 40 km west of Kırşehir province, was built for irrigation. The surface area of Sıddıklı Reservoir (Figure 1) is 1.65 km 2 . Reservoir is used for irrigation of, 4945 ha agricultural area in the region. In addition, fishery activities are carried out economically in the Sıddıklı Reservoir (Anonymous 2011).

Laboratory Processes and Data Analyses
The total and standard lengths of the specimens were measured to the nearest ± 1 mm and weighed with a precision of ± 0.01 g. Sex determination was made by macroscopic and microscopic examination of gonads.
Whether the female to male ratio in the sample is statistically different from the expected 1: 1 ratio was determined by applying the chi-square (χ2) test (Zar 1999).
Gonadosomatic Index (GSI) values of male and females were used to determine the reproduction season. The following formula was used to calculate this index (Devlaming et al. 1982).

= × 100
GW is the gonad weight and W is the fish weight.
The number of eggs in fish ovaries was calculated by gravimetric method (Le Cren 1951).

= ×
F is the total number of eggs in the ovary, n is the number of eggs in the sample from the ovary, G is the weight of the ovary (g), and g is the weight of the sample taken from the ovarium (g). Relative fecundity was calculated by dividing total fecundity with total weight of fish. After eggs of S. glanis photographed, egg diameters were measured by the Mshot image analysis system. The relationships of total fecundity-length and total fecundity-weight were determined using exponential and linear regression models. The model obtained high correlation value was chosen model explaining to relations.

Sex ratio
During the study, a total of 200 individuals were examined. Of the total fish examined, 94 (47.0%) were females and 106 (53.0%) were males. Sex ratio was determined as 0.88:1.00 (Female: Male). This ratio was not statistically different from the expected 1.00:1.00 (χ2= 0.841, P>0.05).

Reproduction period
Monthly variations in the mean GSI values of the female and male individual and temperature values were shown in Figure 2 and 3, respectively. The values of GSI were varied from 0.03-11.80 in females and 0.008-0.451 in males. Also, descriptive statistics of GSI values in female, male and all individuals were showed in Table 1. The gonadosomatic index (GSI) of this species was the highest in April when water temperature was 14.9 ºC. The GSI value of female and males increased from February to April. After April, the GSI showed a sharp decrease until June when water temperature was 20.8 ºC. Monthly GSI changes in all samples showed that the reproduction period occurred between April and the end of June (Figure 2). The water temperature in reproduction period was measured as 14.9 ºC in April 18.1 ºC in May and 20.8 ºC in June, respectively.

Fecundity and Egg Diameter
Total fecundity was estimated in 8 females. The minimum, maximum, mean length and weight of 8 females were given in Table 2. The number of eggs in female varied between 9018 and 75938 eggs/individual. The mean total fecundity was 46343eggs/individual. Egg diameters ranged from 1.091 mm to 2.465 mm and mean egg diameter was found as 1.758 mm (Table 2). Relative fecundity for each kilogram of female fish was ranged from 7020 to 17510 eggs and mean relative fecundity was calculated as 13000 eggs.
The relationships between total fecundity-length ( Figure  4) and total fecundity-weight ( Figure 5) were determined as F = 0.0009 x TL 4.045 and F = 2.2433 x W 1.213 , respectively. It was found that the number of eggs (total fecundity) increased in parallel with length and weight increase ( Figure  4-5). Coefficients of correlation showed that there were strong relationships between total fecunditylength (r 2 = 0.830) and total fecundity-weight (r 2 = 0.801) of S. glanis inhabiting Sıddıklı Reservoir.

Discussion
In this study, the sex ratio was found not to be statistically different from the expected 1.00:1.00 (χ2= 0.841, P>0.05). Alp et al. (2004) found that sex ratio was 1.00:0.82 in Menzelet Reservoir and that this ratio was not different from expected 1.00:1.00. Sex ratios were reported as 50.62% male and 49.38% female in Hirfanlı Dam Lake (Doğan Bora and Gül 2004), 60.94% female, 26.56% male and 12.50% unsexed in Altınkaya Dam Lake (Yılmaz et al. 2007), 49.1% of female and 50.9% of male in İznik Lake (Uysal et al. 2009), 40.91% female, 59.09% male in Çelik Lake (Yüngül et al. 2014) and 42.86% female, 57.14% male in Altınkaya Dam Lake (Saylar 2014). In the literature, the numbers of male and female individuals are generally close to each other.
It has been determined that the reproduction period of S. glanis in the Sıddıklı Reservoir continued from April to June according to the monthly GSI changes of all individuals. As a matter of fact, Alp et al. (2004) reported that hunting for S. glanis in Turkey has banned between 1 April and 1 August. It has been reported that this species was breeding from June to August in the Menzelet Reservoir (Alp et al. 2004) and from May to June in Karasu Stream (Akyurt 1988). In this study, the water temperature in reproduction period was measured as 14.9 ºC in April 18.1 ºC in May and 20.8 ºC in June, respectively. Akyurt (1988) found that the water temperature in the prior of reproduction season in Karasu Stream was 16-18 ºC. In other rstudies, the water temperature at the time of reproduction was noted as 15-18 ºC (Slastenenko 1956) and 18-22 ºC (Copp et al. 2009). The results of this study are quite compatible with other studies in terms of both reproduction time and water temperature. Also, the spawning season is dependent on the ecological conditions of the habitats and is closely related to the water temperature (Akyurt 1988). For this reason, reproduction time may vary depending on water temperature, latitude and climatic characteristics of habitats.
In this study, total fecundity ranged from 9018-75938 egg/individual and mean total fecundity was determined as 46343 egg/individual. Akyurt (1988) found that S. glanis had 12.700 eggs per kilogram in the Karasu Stream. The mean total fecundity of S. glanis was calculated as 87108 egg/individual (Alp et al. 2004). Copp et al. (2009) reported that the mean total fecundity was found to vary between 14.600-354.000 eggs/individual in S. glanis populations. The total fecundity value obtained in this study was lower than other studies. As a matter of fact, Jones (2009) reported that fecundity decreased because of the slowing of fish growth. The fact that the growth of S. glanis inhabiting in Sıddıklı Reservoir is very slow (Yazıcı 2018) confirms the results of this research. Although there are fishing at least twice each month during the reproductive period in this study, gonads were taken only from 8 fish. The lack of the number of fishes that reached reproduction maturation led to this situation. In this respect, although the value of total fecundity in this study suits the reference values reported by Copp et al. (2009), it is considered that an actual comparison cannot be made. However, relative fecundity for each kilogram of female fish was 13000 eggs in this study. The number of eggs per kilogram 12700 eggs in the Karasu Stream (Akyurt 1988). Alp et al. (1988) found that S. glanis had 8434 eggs per kilogram in the Menzelet Reservoir.
Relative fecundity values of this study were higher than other studies. The weight and lengths of fish in the sample led to this situation.
In this study, it was determined that the egg diameter of S. glanis ranged from 1.091 mm to 2.465 mm and mean egg diameter was 1.758 mm. Akyurt (1988) reported that mean egg diameter of this species was 2.500 mm in Karasu Stream. The diameters of the egg of S. glanis inhabiting Menzelet Reservoir vary between 1.000 mm and 3.630 mm, and the mean egg diameter is 2.130 mm (Alp et al. 2004). According to the results of this study, egg diameters of the S. glanis were lower than the other studies. The lack of the number of fishes that reached reproduction maturation may have caused this situation.
The strong relationships which are exponential. between fecundity and length and fecundity and weight were determined in this study. Also, fecundity increased with the weight and length increases. Alp et al. (2004) reported that there are strong correlations between fecundity and length and fecundity and weight in S. glanis inhabiting Menzelet Reservoir and noted that the number of eggs was closely related to the increase in length and weight (r 2 >0.899).
In conclusion, S. glanis inhabiting Sıddıklı Reservoir performed reproduction activities between April and June. The changing climate conditions due to global warming can be affect the reproduction season of fish. Therefore, constant updating of the reproduction times of the fish species in each habitat and the regulation of fishing bans according to the habitats will be beneficial for the future of fish populations.