Journal of FisheriesSciences.com

Keywords

Exotic fish, Endemic fish, Length-weight relations, Condition, Hirfanli Reservoir

Introduction

The length-weight relationship (LWR) is an important tool in fishery management. Primarily, the relationship between fish length and weight can be used to convert length to weight and vice versa. Fish length is often more rapidly and accurately measured than fish weight (Le Cren1951). In particular, length can be measured more easily than weight during field studies; therefore, weight can be estimated after field studies using the length-weight relationship. Furthermore, length-weight regressions have been used extensively for conversion of growth in length equations to growth in weight equations in the stock assessment models; for estimation of standing-crop biomass when the length frequency distribution is known, and for predicting the condition index (Le Cren 1951; Wootton 1990; Petrakis and Stergiou 1995; King, 1996). Additionally, the LWR is useful for comparing the life history of a species in different regions and/or seasons (Wootton, 1990; Gonçalves et al. 1997) and it can be used for morphological comparison of species and populations (Petrakis and Stergiou 1995; King, 1996).

The length-length relationships (LLR) are also important in fishery management. In ich-thyological researchs different types of fish length measurements are utilized. For instance, standard length (SL) is used in systematic stud-ies, whereas total length (TL) and fork (FL) length are commonly used for estimation of fish growth. Length measurements of fishes should be standardized to facilitate comparison of different populations; therefore, LLR in different populations should be known. LLR is also im-portant for comparative growth studies (Mou-topoulos and Stergiou 2002).

The condition factor is a quantitative param-eter of the state of well-being of a fish. Indices of condition are indirect, but sometimes useful indicators of changes in the growth rate (Wootton 1990). The condition of a fish is indicative of recent physical and biological circumstances (Le Cren 1951); thus, the condition factor provides important information about present and future population success via its association with growth, reproduction, and survival.

The aim of the present study was to describe the condition, LWR and LLR for 5 fish species in Hirfanli Reservoir, Turkey. Of the 5 species presented herein, the endemic species Aphanius danfordii has a natural population, whereas Pseudorasbora parva, Atherina boyeri, Cyprinus carpio, and Tinca tinca were introduced into the reservoir. LWR of the fish species presently dwelling in Hirfanli Reservoir was examined in order to understand the effect of the changes in the ichthyofauna due to fish introductions in the reservoir; however, long-term observation is required to observe the effects of changes in the ichthyofauna on fish populations. We hypothesized that findings of the present study would provide a basis for further evaluation of the changes in fish growth following subsequent illegal introduction of alien species into the reservoir.

Materials and Methods

The specimens included in this study were collected from Hirfanli Reservoir, which is lo-cated on the Kizilirmak River Basin in Central Anatolia (33°31′07.16″ E, 39°16′22.2″N). The dam that created the reservoir was completed in 1953. Although the native fish fauna of the res-ervoir consisted of Cyprinus carpio, Squalius cephalus, Capoeta capoeta, Silurus glanis, Barbus tauricus, Alburnus sp., and Chon-drostoma nasus at the end of the 1960s, it has changed significantly since then due to anthro-pogenic effects. Carp, sander, tench, and crayfish (Astacus leptodactylus) were introduced into the reservoir after the 1970s for fishery management (Anonymous 2005). Today, such non-native species as Pseudorasbora parva and i, and such native endemic species as Aphanius danfordii have dense populations in the reservoir and share the same habitat (Ekmekçi et al. 2010).

Samples were caught monthly from March to November 2008 by trawl net with 5-mm mesh from the lakeshore at a maximum depth of 5 m. Fish specimens were anesthetized using MS 222, preserved in 4% formaldehyde solution and then transported to the laboratory for further analysis. TL, FL, and SL were measured to the nearest 0.05 mm, and weight (W) was measured to the nearest 0.001 g. Sex was determined via macroscopic or microscopic observation. The following relationships were established using linear regression analysis; W-TL, FL-TL, SL-TL, and SL-FL. Log-transformed data were used to establish the LWR. The parameters a and b were calculated using least-squares regression. Both comparison of the slopes of the length-weight regression between sexes and variation in coefficient b from 3 were tested using Student’s t-test (Zar 1999). Fulton’s condition factor (K) was calculated using the equation K = (W/L3) × 100, where W is total body weight (g) and L is total length (cm) (Le Cren 1951).

Results and Discussion

In total, 4598 specimens of 5 fish species be-longing to the families Cyprinidae, Cyprino-dontidae, and Atherinidae were collected from Hirfanli Reservoir. The sample size and the re-lationships between TL, FL, and SL in selected fishes are shown in Table 1. All the examined relationships were significantly linear with all coefficients of determination values (r2 > 0.98, P < 0.01).

Table 1: Relationships between total, fork and standard length for five fish species in Hirfanli Reservoir. TL: Total length in mm, FL: Fork length in mm, SL: Standard length in mm, n: sample size, a and b are the parameters of linear regression analysis

Length range, LWR parameters a and b, standard errors of parameters a and b, and the coefficient of determination (r2) for selected fishes are given in Table 2. All relationships were statistically significant (P < 0.01) and r2values were found close to 1. The LWR expo-nent b varied between 2 and 4, but was often a value close to 3 and a value of 3 indicates iso-metric growth and values other than 3 indicate allometric growth (Tesch, 1971). In the present study, the estimates of the parameter b varied between 2.896 for C. carpio and 3.67 for A. danfordii (Table 2). According to the results, A. danfordii, A. boyeri, P. parva, and T. tinca ex-hibited positive allometric growth (b > 3, P<0.05), versus negative allometric in C. carpio (b < 3, P<0.05).

Table 2: Estimated parameters of the total length-weight relationship and Fulton’s condition factor for five fish species shared same habitat in Hirfanli Reservoir

The LWR can be indicative of spatial and temporal variations related to water temperature, food availability, and reproductive activity (Wootton 1990). LWR parameters a and b are affected by a number of factors, including sex, gonad maturity, health status, season, habitat, nutrition, environmental conditions such as temperature and salinity, stomach fullness, gen-eral fish condition, differences in length range of fish specimens, and collection gear (Froese 2006; Tesch 1971). In Hirfanli Reservoir a slight temporal change was observed in the b value in T. tinca and C. carpio (Table 3); however, there was not a difference in the allometric growth pattern between the 2 populations

Table 3: b values in LWR and K of C. carpio and T. tinca from Hirfanli Reservoir during different periods

Table 2 also shows Fulton’s condition factor (K) for selected species. K ranged from 0.604 for A. boyeri to 1.721 for A. danfordii. Population dynamics studies have shown that high condition factor values indicate favorable environmental conditions (such as habitat and prey availability) and that low values indicate less than favorable environmental conditions (Blackwell et al. 2000). The condition factor fluctuates due to interaction between feeding conditions, parasitic infections, and physiological factors (Le Cren 1951). The condition factor for C. carpio and T. tinca have a tendency of temporal decrease (Table 3). Differences in the condition factor have been considered indicative of various biological features, such as fatness or suitability of the environment (Le Cren, 1951). The temporal decrease in K in both of the species in the present study could be considered indicative of degradation in feeding conditions. On the other hand, a decrease in exponent b and K values in T. tinca are indicative of possible competition between C. carpio and other non-native species recently introduced into the reservoir.

Conclusion

In conclusion, the results provide basic in-formation on the LWR, LLR, and condition of 5 introduced and native fish populations in Hirfanli Reservoir. The temporal changes ob-served in b and K values in the C. carpio and T. tinca populations, which existed in the reservoir prior to the introduction of P. parva and A. boyeri, could be considered an indicator of niche competition between the species. We think long-term monitoring is essential to more clearly determine the effects of recently introduced species on the other species that share the same reservoir habitat, and that such findings would be useful for sustainable fishery management in Hirfanli Reservoir.

Acknowledgments

This research was supported by the Scientific and Technical Research Council of Turkey (TÜBITAK) project no: 107.O.718.

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