Growth, the Length-Weight Relationship, and Reproduction in Vimba (Vimba Vimba L

Turk J Zool 2011; 35(1): 87-96 © TÜBİTAK Research Article doi:10.3906/zoo-0901-16

Growth, the length-weight relationship, and reproduction in vimba (Vimba vimba L. 1758) sampled from an oligo-mesotrophic lake in northwest Anatolia (Turkey)

Hacer OKGERMAN1,*, Mahmut ELP2, Cumhur H. YARDIMCI1 1İstanbul University, Fisheries Faculty, Freshwater Biology Department, İstanbul - TURKEY 2Yüzüncü Yıl University, Agriculture Faculty, Van - TURKEY

Received: 13.01.2009

Abstract: The growth parameters and reproduction period in vimba (Vimba vimba L. 1758) sampled from Sapanca Lake were determined monthly between September 2003 and July 2004. The 335 vimba specimens caught ranged in age from 2+ to 6+ years, and the majority of the samples consisted of individuals of the 4+-year-old age group. The length-weight relationship was estimated to be W = 0.0084 FL3.1797±0.0035 for males (r2 = 0.94, P < 0.05) and W = 0.0089 FL3.1572±0.0033 for females (r2 = 0.93, P < 0.05). Regression coefficients for sex were significant (t-test, P < 0.05). The slope (b) significantly differed (ANCOVA, P < 0.05) between months. The fact that the b values for male and female vimba specimens differed from 3.0 indicates that there was positive allometric growth. The von Bertalanffy equation was determined using Lt = 28.940 (1-exp {-0.123[t+2.193]}), ∅’: 2.030, (r = 0.999) for males and Lt = 24.708 [1-exp {-0.205[t+1.464]}), ∅’: 2.097, (r = 0.999) for females. The sex ratio was 1:1.86 (χ2; P < 0.05). The spawning period of vimba began at the end of April and continued until the beginning of July; the water temperature during this period was between 14.8 and 25.9 °C.

Key words: Vimba vimba L., length-weight relationship, reproduction, von Bertalanffy, Sapanca Lake

Kuzeybatı Anadolu’da oligo-mezotrofik bir gölde eğrez Vimba( vimba (Linnaeus 1758)) balığının büyümesi, boy-ağırlık ilişkisi ve üremesi

Özet: Temmuz 2003-Eylül 2004 tarihleri arasında Sapanca Gölü’nden aylık olarak yakalanan eğrez balığının (Vimba vimba L. 1758) büyüme parametreleri ve üreme periyodu belirlenmiştir. Yakalanan 335 eğrez balığının yaş değerleri 2+ ve 6+ yaşları arasındadır ve çoğunluğu 4+ yaşındaki bireylerden oluşmaktadır. Boy-Ağırlık ilişkisi erkekler için W = 0,0084 FL3,1797±0,0035 (r2 = 0,94, P < 0,05) ve dişiler için W = 0,0089 L3,1572±0,0033 (r2 = 0,93, P < 0,05) idi. Cinsiyetler arasındaki

regresyon katsayısı önemlidir (t-test, P < 0,05). “b” değeri aylara göre önemliydi (ANCOVA, P < 0,05). Dişi ve erkek eğrez balıklarının “b” değeri 3’ten büyüktür ve pozitif allometrik büyüme göstermektedir. von Bertalanffy büyüme eşitliği erkeklerde; Lt=28,940 (1-exp {-0,123[t+2,193]}), ∅’: 2,030, (r = 0,999) ve dişilerde Lt = 24,708 [1-exp {-0,205[t+1,464]}), ∅’: 2,097, (r = 0,999) olarak belirlenmiştir. Cinsiyet oranı 1:1,86’dır (χ2; P < 0,05). Eğrez balığının yumurtlama periyodu Nisan sonunda başlamakta ve Temmuz başına kadar devam etmektedir. Bu dönemdeki su sıcaklığı 14,8 ile 25,4 °C arasındadır.

Anahtar sözcükler: Eğrez balığı, Vimba vimba L., boy-ağırlık ilişkisi, üreme, von Bertalanffy, Sapanca Gölü

* E-mail: [email protected]

87 Growth, the length-weight relationship, and reproduction in vimba (Vimba vimba L. 1758) sampled from an oligo-mesotrophic lake in northwest Anatolia (Turkey)

Introduction in this study to previously reported data in an effort to Vimba vimba L. is known as a benthopelagic improve our understanding of the growth parameters species distributed in the inland waters and lagoons and reproduction period in vimba in Sapanca Lake. of Europe, the Russian Federation, Serbia Montenegro, Slovakia, Croatia, Kazakhstan, Slovenia, Materials and methods Ukraine, and Turkey (Geldiay and Balik, 1988; Pecl, 1990; Froese and Pauly, 2008). This species was Sapanca Lake is located in northwest Turkey (40°41Ń-40°44Ń, 30°09É-30°20É) (Figure 1). The zoogeographically introduced to Turkey from western 2 Thrace, and primarily spread to north and northwest surface area of the lake is 46.8 km , and mean and Anatolia (Geldiay and Balik, 1988). In some places maximum depths are 29 m and 52 m, respectively. this species is of great economic importance. Catches The littoral zone of the lake is dominated by commonly attain lengths of 20-30 cm and weigh 250- Phragmites spp. There are some submerged 500 g; in rare cases they are 40-50 cm and 1-3 kg. macrophytes, such as Chara spp., Myrophyllum spp., Ceratophyllum spp., Potamogeton spp., Najas spp., and The species spawn for the first time at 3-5 years of Nuphar spp. in the lake. According to Numann age, from the end of April until July in gentle currents (1958), and Rahe and Worthmann (1986), 10 fish over a stony bottom. Hindrance of the spawning families were identified in Lake Sapanca (Cobitidae, migration caused by dams and impoundments, as well Cyprinidae, Atherinidae, Clupeidae, Gobiidae, as river pollution, has recently brought about a Balitoridae, Esocidae, Salmonidae, Siluridae, and discernible drop in the number of East European Syngnathidae). Minimum and maximum temperature vimba. Vimba is included on the list of protected of the surface water was 8 and 29 °C, respectively. species, as it is seriously threatened with extinction in Minimum-maximum PO -P, NO -N, and Poland (Witkowski et al., 1999), endangered in 4 3 chlorophyll-a values year round were 0.006-0.063 mg Austria (Schiemer and Spindler, 1989), and vulnerable -1 -1 3 L , 0.043-0.344 mg L , and 7.97-21.59 mg/m , in the Czech Republic (Lusk et al., 2004). Since 1985, respectively (Yılmaz, 2002). Aykulu et al. (2006) also including the latest evaluation in 2000, vimba has reported that this lake tends to convert from an been classified as a near-threatened (NT) species in oligotrophic to oligo-mesotrophic state. Finland (Finnish Game and Fisheries Research Institute, 2008). According to the International Union Vimbas were caught in Sapanca Lake between for Conservation of Nature (IUCN), vimba is listed in September 2003 and July 2004 (at monthly intervals). the least concern (LC) category. In the inland waters Vimba specimens were sampled at 5 stations in of Turkey the vimba is now declining in number Sapanca Lake (Figure 1). All fish specimens were because of over-fishing, particularly during its caught using gill nets of various mesh size (10, 22, 26, spawning period; however, the state of vimba in 30, 34, 38, 42, 48, and 50 mm knot to knot). The study inland waters of Turkey has yet to be determined. sample included 335 vimbas (118 males and 217 Sapanca Lake is largely used for commercial and females). Fish were brought to the laboratory soon recreational fishing purposes, as well as a source of after capture. The fork length (FL) of each fish was drinking water and industrial water. Fewer vimba measured in the laboratory (to the nearest 0.1 cm) and (8.71%) are caught in Sapanca Lake than rudd the fish were weighed in grams (to the nearest 0.1 g). [Scardinius eryhthrophthalmus L. (24.43%)], white The sex of the specimens was determined by bream [Blicca bjoerkna L. (22.98%)], and roach macroscopic and microscopic observation of the [Rutilus rutilus L. (21.71%)] (Karabatak and gonads. Scales on the left side of the body between the Okgerman, 2002), as vimba is over-fished due to its lateral line and dorsal fin were collected and analyzed high commercial value. The aim of the present study between 2 slides in order to determine age (Lagler, was to determine the length-weight relationship, 1966). growth, and reproduction period in vimba from Growth was investigated by applying the von Sapanca Lake, an oligo-mesotrophic lake in northwest Bertalanffy growth function to pooled size-at-age and Turkey. In addition, we compared the data obtained weight-at-age data for both sexes using standard non-

88 H. OKGERMAN, M. ELP, C. H. YARDIMCI

Figure 1. Sapanca Lake; location of sampling stations. linear optimization methods. The von Bertalanffy regression slopes (Zar, 1996). Student’s t-test was used growth function was calculated as follows: Lt = L∞ (1 to compare the parameters obtained from all grouped

– exp {-K[t-to]}) (von Bertalanffy, 1938), where Lt is data (general coefficient), using data grouped by length at age t, L∞ is asymptotic length, k is the month (monthly coefficients). growth coefficient, and to is the hypothetical age at The overall sex ratio was determined. The which length is equal to zero (Ricker, 1975; Sparre and difference between sex ratios was tested using χ2 (chi- ∅ Venema, 1992). The growth performance index ( ’) square) (Zar, 1996). The gonads were removed and (Pauly and Munro, 1984) was calculated using the weighed to the nearest 0.1 g. The gonadosomatic ∅ equation ’= log10(K) + 2log10(L∞). index (GSI %) (gonad weight/total body weight × 100) The relationship between the length (L) and (Ricker, 1975) was calculated for each fish and all weight (W) of a fish is usually expressed by the values were averaged on a monthly basis. Each equation W = aLb; a and b, the coefficient of sampling month the water temperature was measured determination (r2), and the standard errors (SE) were to determine the relationship between temperature estimated over the entire study period by least squares and gonad growth. Statistical analyses were carried regression using the log-transformed weights and out using SPPS for Windows v.11.0 and Statistica v.6. sizes. In order to confirm whether b-values obtained in the linear regressions were significantly different from the isometric values we used the t-test with a Results confidence level of ±95% (α = 0.05) (Sokal and Rohlf, Female and male vimbas were distributed in age 1987). Additionally, the t-test was used to compare groups of 2+-6+ years; the 4+-year-old age group was regression lines between the sexes, and to test the the most abundant (40.9%). Fork length ranged from significance of the differences between slopes (b) and 9.1 to 22.9 cm and weight ranged from 12.31 to 236.81 intercepts (a) (Zar, 1996). When testing the g (Table 1). The difference in growth between male differences between months, analysis of covariance and female vimbas was significant (P < 0.05). Body (ANCOVA) was used to compare the vimba weight calculations made according to sex and age

89 Growth, the length-weight relationship, and reproduction in vimba (Vimba vimba L. 1758) sampled from an oligo-mesotrophic lake in northwest Anatolia (Turkey)

Table 1. Mean fork length (FL [cm]), mean weight (W [g]) and standard error (±SE) for different age groups of male and female vimbas caught in Sapanca Lake in 2003 and 2004.

FL ± SE (MALE) W± SE (MALE) FL ± SE (FEMALE) W± SE (FEMALE) Age N N P*=0.05 P**=0.05 (min-max) (min-max) (min-max) (min-max)

12.21 ± 0.35 24.38 ± 2.22 12.62 ± 0.44 27.47 ± 3.72 2+ 13 10 P > 0.05 P > 0.05 (10.60-14.20) (15.19-38.75) (10.90-15.10) (15.53-46.83)

14.06 ± 0.29 40.69 ± 2.65 14.58 ± 0.27 46.49 ± 2.88 3+ 37 61 P > 0.05 P > 0.05 (9.10-17.70) (18.12-94.50) (10.40-18.80) (12.31-105.27)

15.60 ± 0.16 54.77 ± 1.78 17.03 ± 0.18 71.38 ± 2.24 4+ 49 88 P < 0.05 P < 0.05 (11.90-18.30) (26.00-95.20) (13.40-21.20) (28.63-142.00)

17.09 ± 0.26 69.01 ± 3.37 17.87 ± 0.24 82.75 ± 3.97 5+ 18 43 P < 0.05 P < 0.05 (15.50-18.90) (39.33-90.90) (15.40-22.20) (47.85-173.34)

19.43 ± 0.56 103.58 ± 12.53 6+ 1 19.30 94.50 15 P > 0.05 P > 0.05 (16.10-22.90) (51.03-236.81) N: number of vimba (V. v imba L.); values of P: significance level; min-max: minimum and maximum value *Significance values belong to FL values **Significance values belong to W values showed that female vimbas were heavier than male The estimated length-weight relationship (LWR) vimbas. Differences in length and weight between the was W= 0.0084 FL3.1797±0.0035 for males (r2 = 0.94, n = female and male vimbas were significant in the 4+- 118, P < 0.05) and W = 0.0089 FL3.1572±0.0033 for females + and 5 -year-old age groups (P < 0.05) (Table 1). (r2 = 0.93, n = 217, P < 0.05). The regression The observed age-length data and the fitted von coefficient for sex was significant (t-test, P < 0.05). Bertalanffy curve are presented for each sex in Figures The slope (b) differed significantly (ANCOVA,, P< 2 and 3. Von Bertalanffy growth equations were 0.05) with respect to the time of month for vimba. estimated as Lt = 28.94 [1-e-0.123(t+2.193)] for males LWR curves of the samples are shown in Figure 4. The and Lt = 24.708 [1-e-0.205(t+1.464)] for females. The general coefficient of allometry was 3.1649. The growth performance index (∅’) was 2.030 for males differences between the general coefficient of and 2.097 for females. allometry (all data) and the monthly coefficients were

30 30 observed values observed values males females 25 25 expected values expected values 20 20 15 15 10 10 Fork length (cm) Fork length (cm) L tfemale = 24.708(1-exp{-0.205[t+1.464]}); r : 0.999; n: 217 5 Ltmale = 28.940(1-exp{-0.123[t+2.193]}); r : 0.999; n:118 5 0 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Age (year) Age (year) Figure 2. Age-length relationships of male vimbas (V. v imba L.) Figure 3. Age-length relationships of female vimbas (V. v imba L.) caught in Sapanca Lake in 2003 and 2004. caught in Sapanca Lake in 2003 and 2004.

90 H. OKGERMAN, M. ELP, C. H. YARDIMCI

250 Vimba vimba 8 n : 118 male 7 Vimba vimba n : 217 female 6 n:335 200 W = 0.0080L3.1572±0.0033 female 5 4 3 150 2 b male+female

GSI%;the exponent'b' 1 GSI male+female 0 100 W = 0.0084L3.1797±0.0035 Total weight(g) male 3 4 4 p.03 .0 b.04 .0 J.04 J.04 e e Ap.04 M 04 S Oct.03 Nov.03Dec.0 Jan F Ma Months 50 Figure 5. Connection between values of gonadosomatic index (GSI) and the exponent ‘b’ of vimbas (V. v imba L.) for 0 each month in Sapanca Lake in 2003 and 2004. 0 5 10 15 20 25 Fork length(cm) Figure 4. Length-weight relationships of male and female vimbas χ2 (V.v imba L.) in Sapanca Lake in 2003 and 2004. males to females was 1:1.86, and (chi-square) analysis showed that there was a significant difference from the expected ratio of 1:1 (P < 0.05). Gonad significant (95% CL) for all months analyzed (Table development, determined by the gonadosomatic 2). index (GSI), was at its maximum for males in May There was a relationship between the (5.708 ± 0.479) and for females in April (8.772 ± gonadosomatic index (GSI) and the exponent b for 0.636) (Figure 6). The GSI increased in females in each month in Sapanca Lake (Figure 5). March, peaked in April, and declined in early July. The In all, 118 of the specimens were male (35.2%) and temperature during the vimba reproduction period 217 were female (64.8%). The overall sex ratio of ranged between14.8 and 25.9 °C (April-July).

Table 2. Length-weight relationships of vimba for each month and also the whole year in Sapanca Lake.

2 Months n FL (cm) a b SE (b) 95% CI r P Growth type

September 2003 8 15.1-17.7 0.2193 2.0307* 0.0056 0.010 0.879 < Allometric (-) October 2003 16 17.2-22.9 0.0049 3.2922* 0.0058 0.011 0.907 < Allometric (+) November 2003 39 11.9-22.4 0.0357 2.6511* 0.0066 0.013 0.920 < Allometric (-) December 2003 10 14.9-19.4 0.0011 3.8650* 0.0091 0.017 0.948 < Allometric (+) March 2004 44 14.3-22.8 0.0031 3.5402* 0.0034 0.006 0.974 < Allometric (+) April 2004 37 14.2-21.3 0.0063 3.3102* 0.0028 0.005 0.979 < Allometric (+) May 2004 82 9.1-19.1 0.0036 3.5024* 0.0048 0.009 0.952 < Allometric (+) June 2004 35 11.0-19.8 0.0180 2.8624* 0.0053 0.010 0.965 < Allometric (-) July 2004 64 10.6-20.0 0.0050 3.3703* 0.0050 0.009 0.958 < Allometric (+) General 335 9.1-22.9 0.0087 3.1552 0.0025 0.005 0.938 < Allometric (+) n: number of individuals; FL: fork length, cm (length range); a: a coefficient related to body form; b: allometric coefficient; SE (b): 2 Standard error of b; IC % 95: Confidence level of b (α = 0.05); r : Determination coefficient; *: P < 0.01: Student’s t-tests for differences between allometry coefficient (b) of monthly and yearly data set

91 Growth, the length-weight relationship, and reproduction in vimba (Vimba vimba L. 1758) sampled from an oligo-mesotrophic lake in northwest Anatolia (Turkey)

10 9 Vimba vimba 8 n male=118 7 n female =217 6 5 GSI% 4 3 2 GSI-male 1 GSI-female 0

03 4 0 J.04 J.04 ep.03 ct.03 ov.03 ec. an.04 eb.04 a.04 p.04 M S O N D J F M A Months

Figure 6. Values of gonadosomatic index of male and female vimbas (V. vimba L.) caught in Sapanca Lake in 2003 and 2004.

Discussion al., 2003), effect of different areas, sex, stomach The exponents of the estimated LWR for male and fullness, age, health, or preservation techniques female vimbas in Sapanca Lake exhibited positive (Tesch, 1971; Treer et al., 1998, 1999). allometry (bmale: 3.1797 ± 0.0035; bfemale: 3.1572 ± Despite vimba’s wide distribution, information on 0.0033), and significantly differed between the sexes the biology of this species in Turkey is scarce. Vimbas (t-test, P < 0.05) and months (ANCOVA, P < 0.05). over 7+ years of age were not observed (Table 3), apart The value of b in Karacaoren-I Dam Lake was 3.23 for from 11+-year-old vimbas caught in the Rega River male and 3.20 for female vimbas (Becer and Ikiz, (Trzebiatowski and Naroźański, 1973). The growth 2001). In the Kirmir Stream of the Sakarya River the rate for length and weight in the present study was value of b was reported as 3.31 for males and 3.59 for relatively low in comparison with populations from females (Tutucu, 2002). The reproduction process other regions (Table 3). When compared to the von (spawning and gonad activity) and changes in food Bertalanffy growth equations in the literature, the uptake could cause monthly variations in length- growth of vimba in Sapanca Lake was lower than that weight relationship parameters (Andrade and of other populations, and in the Berounka River Campos, 2002). The differences between all the (Czechoslovakia) growth is quite rapid, with rather monthly coefficients were significant (95% CL). The high k values (Table 4). b value was at its lowest level in September (2.0307 ± The growth performance index of vimba (∅’) in 00.56) and highest in December (3.8650 ± 0.0091). Sapanca Lake was lower than that previously reported This result was most probably because of the scarcity (Table 4). In accordance with the sexual dimorphism or abundance of food, and the small number of in size mentioned previously, the estimated specimens caught during these months. The asymptotic length (L∞) of male vimbas was higher reproduction process (spawning and gonadal activity than that of females. The estimated asymptotic length in June) and changes in food uptake, or fewer for males was much greater in comparison with the individuals (in September and November) could size of the largest male in the study. We think that the cause negative allometry in the length-weight reason of this was that only one individual of the 6+ relationship parameters. Furthermore, the differences age group was effectively sampled. The asymptotic in b values may have been due to the influence of length (L∞) was higher than expected because the water quality or food availability on fish growth individual in question (6+) had a mean length value (Momsen, 1998), differences in sampling, the number greater than that of the previous age group (5+). On of specimens, length range of the species (Morey et the other hand, the estimated growth rate (k), which

92 H. OKGERMAN, M. ELP, C. H. YARDIMCI

Table 3. Mean length (FL, SL, TL; cm), mean weight (W,g) values according to age and sex of vimba (V. vimba L.) in different localities and Sapanca Lake.

Age References Location

0+ 1+ 2+ 3+ 4+ 5+ 6+ 7+

1 Volkhov R (SL) - 5.7 11 16.1 21.2 25.3 28.3 30.4 1 Dinyeper R (SL) - 6.2 11 17 23.0 28.0 32.0 35.0

2 Sariyar DL (FL) - - 10.45 14.61 16.98 19.12 20.97 23.12 (W) - - 13.50 42.02 74.55 112.05 161.07 235

3 Karacaören-I- DL (FL) 14.9 16.96 18.94 21.58 23.9 24.9 25.64 26.6 (W) 4.8 66.75 97.30 150.55 202.46 227.66 270.42 319

4 Sakarya R Kirmir S (FL) 10.62 13.01 15.01 17.78 19.54 - - (W) - 15.64 31.89 51.52 88.70 124.42 - -

M (TL) - 6.3 12.4 18.7 23.9 - - - 5 Barycz R (W) - 2.4 18.0 68.4 147.8 - - - F (TL) - 6.2 12.2 17.9 23.5 - - - (W) - 2.25 17.1 67.6 145.9 - - -

M (FL) - - 12.21 14.06 15.60 17.09 19.30 - 6 Sapanca L (W) - - 24.38 40.49 54.77 69.01 94.50 - F (FL) - - 12.62 14.58 17.03 17.87 19.43 - (W) - - 27.47 46.49 71.38 82.75 103.58 -

1: Berg, 1949; 2: Ekmekci and Erk’akan, 1992; 3: Becer and Ikiz, 2001; 4: Tutucu, 2002; 5: Łuszczek- Trojnar et al, 2008; 6: Present Study; R: River; L: Lake; DL: Dam Lake; S: Stream; M: Male; F: Female.

Table 4. von Bertalanffy growth parameters and derived index of growth performance (∅’) for population of vimba (V. vimba L.) by author and study area.

∅ L∞ kt0 ’ r Localities References

27.80 (SL) 0.218 -0.22 2.23 - Berounka River Hanel, 1991 52.0 (TL) 0.190 -0.70 2.71 - Europe Froese and Binohlan, 2003 28.940* (FL) 0.123 -2.19 2.030 0.999 Sapanca Lake Present study 24.708**(FL) 0.205 -1.46 2.097 0.999

*male; **female is generally inversely correlated with L∞, was higher vimba between localities might have been because in females than in males (Table 4). The to values Sapanca Lake is south of those other localities, obtained for male and female vimbas were very insufficient food supply in food habitats, water negative in the present study, as compared to those temperature, competition for food between vimba obtained at other localities (Table 4). The high to and the other cyprinid species with very similar values may be attributed to the lack of young-of-the- feeding habits, and differences in the stage of year specimens. The differences in the growth of ontogenetic development of vimba, such as condition,

93 Growth, the length-weight relationship, and reproduction in vimba (Vimba vimba L. 1758) sampled from an oligo-mesotrophic lake in northwest Anatolia (Turkey)

Table 5. Reproduction season according to Gonadosomatic Index (GSI) value, of vimba (V. v imba L.) in different localities and Sapanca Lake.

Reproduction season T. (°C) Localities References

Between May and July Sariyar D. L. (Turkey) 1 Between May and July Kirmir S. of Sakarya R. (Turkey) 2 Between April and June Karacaören-I D. L. (Turkey) 3 Between June and mid-July Volkhov R. (Russia) 4 May Dnieper R. (Ukraine) 4 From late May to late June 18-29 Sefid-roud R. (Iran) 5 Between May and mid-June 13-15 In Finland 6 Between April and June Rhine R. (Germany) 7 Between April and June In Turkey 8 From late April to beginning of July 14.8-25.9 Sapanca L. (Turkey) 9

T: Temperature; D.L.: Dam Lake; S: Stream; R: River; L: Lake; 1: Ekmekci and Erk’akan, 1992; 2: Becer and Ikiz, 2001; 3: Tutucu, 2002; 4: Berg, 1949; 5: Abbasi et al., 2005; 6: Finnish Game and Fisheries Research Institute, 2008; 7: Billard, 1997; 8: Balik, S. 1995; 9: Present study. length, age, sex, and gonadal development (Ricker, climatic conditions. The spawning period of fish may 1975). be affected by altitude, temperature, and food quality, In Sapanca Lake the reproduction season of vimba as well as ecological factors, such as stagnant water began at the end of April and extended to the and running water (Nikolsky, 1963). beginning of July, with maximal gonadal activity in Consequently (bearing in mind the results of the June (Figure 5); however, the maximum GSI was present study), the growth of vimba in Sapanca Lake observed in September, though the cause of this high was dependent upon the b value. We suggest that GSI value is unknown. According to field and fishing in the lake be prohibited from April to July in laboratory observations, vimba does not perform order to ensure maximum productivity of the vimba secondary reproduction in September. Water population. If this prohibition is not enforced extreme temperature is the principal environmental factor fishing pressure on spawning stock will negatively affecting the reproduction of fish. During the affect the stock. In addition, in order to ensure the reproduction period water temperature was 14.8 °C continuity of a sustainable vimba stock in Sapanca (April), 18.7 °C (May), 25 °C (June), and 25.9 °C Lake the minimum catch length for fish should be (July). Gursoy (2001) reported that the vimba in more than 17.03 cm (FL) and 4+ years should be the Sapanca Lake reached sexual maturity at 18.7 cm (TL) minimum age. and 3+ years of age. The gonadal maturity age of vimba in Sariyar Dam Lake, in Karacaören-I Dam Lake, and in the Kirmir Stream of Sakarya River was Acknowledgements also 3+ years (Ekmekci and Erk’akan, 1992; Becer and We thank the Research Fund of the University of Ikiz, 2001; Tutucu, 2002) (Table 5). In Finland, vimba İstanbul (project number: 93/15052003) for spawn for the first time at 7-8 years of age, when they supporting this study. We are also grateful to are about 25 cm long. The start and end dates of Nizamettin Şahin and Adnan Sümer for their help spawning may vary due to different ecological and conducting the fieldwork.

94 H. OKGERMAN, M. ELP, C. H. YARDIMCI

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