A study on some biological parameters of the population of Chondrostoma angorense Elvira, 1987 (Actinopterygii: Cypriniformes: Leuciscidae) in the Devrez River, Türkiye

The study was conducted in the Devrez River, situated in the northern part of Anatolia, Türkiye (Fig. 1). Fish samples were collected from five different sampling sites with the following coordinates—Sampling site 1: 40°58′34″N, 34°04′40″E; Sampling site 2: 40°53′58″N, 33°39′30″E; Sampling site 3: 40°50′16″N, 33°23′46″E; Sampling site 4: 40°46′37″N, 33°17′05″E; Sampling site 5: 40°37′02″N, 33°02′08″E. The Devrez River is a large tributary of the Kızılırmak River basin, spanning 186 km in length, with a basin area of 336 400 ha and a flow rate of 4.081 m³ · s⁻¹. The region’s climate is influenced by both the oceanic climate of the Black Sea region and the terrestrial climate of Central Anatolia. Precipitation fluctuates annually within the basin, ranging from 348 mm to 545 mm. The basin experiences lower precipitation levels, below Türkiye’s average (573.4 mm), mostly concentrated in winter and spring, contributing to irregular flow patterns. The ground of the Devrez River is stony and sandy, forming deep ponds in some places (DSI, 2014). The fish species in the Devrez River include C. angorense, C. tinca, B. anatolicus, Alburnoides freyhofi, Alburnus escherichii, Alburnus goekhani, Oxynoemacheilus angorae, Oxynoemacheilus samanticus, Oxynoemacheilus seyhanensis, Rhodeus amarus, Neogobius fluviatilis, Pseudorasbora parva, Squalius sp., Alburnus derjugini, and A. escherichii (Gürbüz, 2023; Yoğurtçuoğlu et al., 2020).

Figure 1

Map of the Devrez River and sampling sites.

In total, 103 fish samples were collected monthly from April 2020 to March 2021 using cast nets with mesh sizes ranging from 12 mm to 25 mm, with assistance from local fishermen. The captured samples were stored in ice and transported to the Hydrobiology Laboratory, Ankara Haci Bayram Veli University. The fork length (FL) and total length (TL) were measured to the nearest 1 mm using an L-shaped board, and an electronic balance (ISOLAB I.602.31.006; Eschau, Germany) was used to record body weight (W) to the nearest 0.1 g immediately. Age was determined from scales, which were taken above the lateral line, below the anterior part of the dorsal fin (Lagler, 1956). All fish specimens were dissected. Gonads were removed, weighed to the nearest 0.01 g using an electronic balance, and preserved in 4% formaldehyde. Sex was assessed by visually inspecting gonad tissue in larger fish and using a stereo microscope (ISOLAB LM18133M010) for smaller ones.

The length–weight relationship was determined using the equation: (1) W=aLb $$W = aL^b $$ which can be transformed into its logarithmic form: (2) log W=log (a)+b×log (L) $$\log \,W = \log \,(a) + b \times \log \,(L)$$ where W is the total weight (g), L is the FL (cm), b is the growth exponent, and a is a constant. The growth exponent b generally lies between 2.5 and 3.5, but the relationship is reported to be isometric when b = 3 and allometric when b is a value other than 3 (Ricker, 1975).

Growth in terms of length was estimated using the von Bertalanffy growth function (VBGF): (3) Lt=L∞ (1-e-K(t-t0)) $$L_t = L_\infty \,(1 - e^{ - K(t - t0)} )$$ where Lt is the length at age t, L_∞ is the theoretical maximum (or asymptotic) length that the species would reach if it lived indefinitely, K is a growth coefficient that is a measure of the rate at which maximum size is reached, and t₀ is the hypothetical age at length zero. Fulton’s CF was calculated using the formula: (4) CF=(W/L3)×100 $${\rm{CF}} = (W/L^3 ) \times 100$$ where W is the total weight (g) and L is the FL (cm) (Ricker, 1975).

The stage of gonadal development was identified for each female individual. Gonadal maturity was assessed using a six-stage scale (Nikolsky, 1963). The stages are as follows:

Stage I: Immature individuals that have not yet spawned.

Sexual maturity and spawning periods were determined based on monthly variations in the GSI and the diameters of oocytes in the samples (Nikolsky, 1963). The GSI was calculated monthly for each fish using the equation: (5) GSI%=(Wg/Wt)×100 $${\rm{GSI}}\% = (Wg/Wt) \times 100$$ where Wg and Wt are the gonad weight (GW) and total body weight of fish (g), respectively. The monthly mean GSI was depicted on a line graph, where the increasing peak denotes the spawning season for the species.

The size at first sexual maturity is defined as the length at which 50% of the captured individuals reach maturity (L₅₀) during the breeding season. This was calculated based on the percentage of mature individuals reaching stage III and above within each size class, and a logistic function was fitted to the proportion of mature individuals by size class using non-linear regression. The function used was: (6) Pr=1/[1 + exp (-r(L-Lm))] $${\mathop{\rm P}\nolimits} _r = 1/[1\, + \,\exp \,( - r(L - L_m ))]$$ where P_r is the proportion mature in each size class, r (−b slope) is a parameter controlling the shape of the curve, and L_m is the size at 50% maturity (L_m = a/r), where a is the x-axis intercept (Saila et al., 1988).

Fecundity (F) was calculated using the gravimetric method described by Bagenal and Braum (1978), involving a 2-hr rinsing of the ovaries with water, followed by the extraction of three 1 g subsamples from the front, middle, and rear portions of each mature ovary. The oocytes in the subsamples were counted. The total number of oocytes in each ovary was proportional to total ovary weight. Relative fecundity (F_r) was calculated as: (7) Fr=F/W(g) $$F_r = F/W(g)$$ where W is the body weight of fish (g), and (8) Fr=F/FL (cm) $$F_r = F/{\rm{FL}}\,({\rm{cm}})$$

Relationships between F and FL; F and W, F, and GW; and F and age (t) were determined using the equation: (9) F=axb $$F = axb$$ where F is fecundity; x is FL, W, GW, or t; a is a constant; and b is an exponent (Bagenal & Braum, 1978). The diameters of 30 oocytes sampled from the front, middle, and rear sections of mature ovaries were measured using a micrometer.

Chi-square (χ²) analysis was used to compare the sex ratio of males to females with the theoretical sex ratio of 1:1. The significance of differences in growth, mean CF values, and mean TL-at-age between males and females was determined using Student’s t-test, with differences considered significant at the a α < 0.05 level. The data were analyzed using Microsoft Excel and Grapher 3. The results were expressed as mean ± standard deviation (SD). The coefficient of determination (r²) was employed to quantify the strength of the linear relationship. The sizes and numbers of oocytes from three different parts of the ovary were statistically compared using a single-factor analysis of variance (ANOVA).

Overall, 103 C. angorense were aged, with the age-3 group being dominant (45.6%) in the population (Table 1). Males were dominant in the younger age groups, and there were only two female fish greater than 4 years of age. The sex ratio of males (n = 51) to females (n = 52) was 0.98:1.00, which did not differ significantly from a ratio of 1.00: 1.00 ((χ² = 0.02 < (χ²_1,0.05 = 3.84). The mean TL ranged from 13.2 cm for 1-year-old fish to 23.7 cm for 5-year-old fish (Table 1). Males in the 2- and 3-year age groups were longer than females in the population. The differences between the mean TL of males and females were not statistically significant (Student’s t-test, t = 0.27; d.f. = 101; p > 0.05).

The estimated relationship between length and weight was log W = −1.8386 + 2.8998 log (L) for males (n = 51; r² = 0.965), log W = −2.0315 + 3.0688 log (L) for females (n = 52; r² = 0.947), and log W = −1.9586 + 3.0039 log (L) for the sexes combined (n = 103; r² = 0.944). The growth of C. angorense population in the Devrez River was found to be isometric (Fig. 2), but males showed negative allometric growth (b = 2.8998). The slope values for males, females, and combined sexes did not significantly differ from 3.0 when compared with a t-test (p > 0.05). The VBGF equations were, respectively, estimated as follows for males, females, and the sexes combined: L_t = 22.58 (1-e^{−0.4596 (t + 0.647)}), L_t = 27.43 (1-e^{−0.3285 (t + 0.954)}), and L_t = 32.64 (1-e^{−0.109 (t + 1.870)}). Differences in growth parameters were observed between the sexes, and as a result, L_∞ was found to be greater in females compared to males (27.43 vs 22.58, respectively). The growth coefficient K, which is proportional to the rate at which fish reach L_∞, was greater in males (0.4596) compared to females (0.3285). There were no significant differences in expected lengths and observed lengths between males and females (Student’s t-test, t = 0.58; d.f. = 101; p > 0.05).

Figure 2

Length–weight relationship of the sampled C. angorense.

Mean CF values ranged from 1.10 to 1.22 for both sexes with a mean (±SD) of 1.12 ± 0.09 (Table 1). The monthly mean CF values for males and females ranged from 1.05 to 1.14 (mean; 1.09 ± 0.07) and 0.80 to 1.19 (1.13 ± 0.12), respectively, indicating that the population is growing in good health. The monthly mean CF for both sexes showed remarkable consistency, with a slight variation noted in some months (Fig. 3). There were no significant differences in mean CF values between males and females in all age groups (Student’s t test, p > 0.05).

Figure 3

Monthly variations in CF (mean ± SD) of C. angorense. CF, condition factor; SD, standard deviation.

Maturity of ovaries exhibited monthly variations throughout the year. The mean GSI values varied from 2.56 to 13.34 in females and from 1.28 to 3.58 in males, with overall higher values in females than in males. Monthly fluctuations were observed in GSI values for both sexes, with the peak occurring in March (Fig. 4), followed by a decline in June. Besides a few minor discrepancies, the general pattern remained consistent across both sexes. Ripe and spent fish ovaries were observed from March to June in this study. These results show that spawning occurred from March (GSI = 13.34) to June (GSI = 2.56). Following spawning, a quiescent phase of approximately 5 months (June–October) was observed, characterized by stable GSI values.

Figure 4

Monthly variations in GSI and oocyte diameter values with SD of C. angorense. GSI, Gonadosomatic Index; SD, standard deviation.

The smallest TL is 11.4 cm and the largest is 24.0 cm (mean 19.2 cm ± 2.88 cm) in females. In male individuals, the smallest TL recorded is 11.8 cm and the largest is 24.1 cm (mean 18.6 cm ± 2.54 cm). The smallest mature female captured was 16.1 cm TL (34 g total weight) and the smallest mature male was 13.3 cm TL (19.5 g total weight). Female C. angorense attained sexual maturity at sizes very similar to those of males. The maturity ogives showed that 50% of females and males were sexually mature at TLs of 16.0 cm and 14.0 cm, respectively (Fig. 5). The observed difference in mean sexual maturity length (L_m) between the two sexes was not significant (χ² = 0.03; p > 0.05). The first spawning age was three for females and two for males.

Figure 5

Ogive of first maturity for females and males of C. angorense.

The number of oocytes of 19 females at maturity stages IV and V ranged from 1015 (16 cm TL and 27 g body weight) to 10 664 (23.5 cm TL and 138 g body weight), while the mean absolute fecundity was 5130 ± 3246. The value of relative fecundity was 256 ± 141 oocytes cm⁻¹ of length (range 62–498 oocytes cm⁻¹) and 59 ± 21 oocytes g⁻¹ of total body weight (range 11–95 oocytes g⁻¹). No significant differences were found in the oocyte size between different parts of the ovaries (F = 0.15; d.f. = 2; p = 0.85). There were also no significant differences in the oocyte number between different parts of the ovaries (F = 0.07; d.f. = 2; p = 0.92). The relationships between fecundity and the four different variables (FL, W, GW, and t) are shown in Fig. 6. The strongest correlation was evident in the comparison of fecundity and GW (R² = 0.9865). The mean oocyte diameter was the smallest in June (0.68 mm) and the largest in March (1.56 mm). Oocyte diameters of mature females increased significantly from September to March (Fig. 4).

Figure 6

Relationship between fecundity and FL, GW, total weight, and the age of female C. angorense. FL, fork length; GW, gonad weight.