R. Patimar*, A. Biniaz**, N. M. Sedaghat*
*Higher Education Institutes of Gonbad, Gorgan University, Gorgan University
of Agricultural Sciences and Natural Resources, Gorgan, Iran, email@example.com
**Fisheries Organization of Golestan, Gorgan, Iran
ВОЗРАСТ, РОСТ И РАЗМНОЖЕНИЕ CARASSIUS AURATUS
В МЕЖДУНАРОДНЫХ ВОДНО-БОЛОТНЫХ УГОДЬЯХ ПРОВИНЦИИ ГОЛЕСТАН (СЕВЕРНЫЙ ИРАН): ПЛАСТИЧНОСТЬ ВИДОВ
Р. Патимар*, A. Биниаз**, Н. M. Седагат*
*Университет Горгана, **Организация рыболовов Голестана,
Горган, Иран, firstname.lastname@example.org,
Age, growth and reproduction of C.auratus Linnaeus, 1758 were investigated in the Alma-Gol and Ala-Gol (northern Iran) from September 2000 to August 2002. From a total of 1448 specimens, the estimated ages ranged from 0+ to 8+ years. C.auratus grew allometrically, negatively in Alma-Gol and positively in Ala-Gol. The parameters to the von Bertalanffy growth curves fitted to mean total lengths at age were yield as Ltmales=183.33(1–e–0.31(t+1.05)) and Ltfemale=245.66(1–e–0.19(t+1.21)) for Alma-Gol population and Ltmale=224.79(1–e–0.24(t+0.83)) and Ltfemale=242.80(1–e–0.23(t+0.80)) for population from Ala-Gol. The value of f´ index varied from 9.25 to 9.51 for the studied populations. The unbalanced overall ratio of males to females was 1 : 10 in Alma-Gol and 1 : 12.7 in Ala-Gol. The reproductive period for this species in these particular wetlands is February, March and April with the maximum GSI recorded values of 2.19 and 2.17 for males and 10.37 and 10.49 for females in Alma-Gol and Ala-Gol respectively.
In the studied habitats (Kordjezi, 1998; Sayyad-Bourni et al., 2001; Shoeiry, 2001; Present study) that differed in environmental factors (tº, pH, EC and S‰), C.auratus showed differences in life history parameters among populations. The lifespan of the population in the studied wetlands was relatively long, with nine age groups being evident. This is different from the patterns observed in their distribution range from south Caspian basin. A comparison shows that C.auratus populations vary greatly in maximum age attained. There are fewer age groups in estuaries than wetlands. The study area is wetland habitat with almost stable conditions, characteristics which might have determined the greater longevity. Differences obtained in age composition and longevity could be explained on the basis of the different exploitation patterns and/or ecological conditions. In this sense, while the C.auratus is not subject to commercial exploitation in the south Caspian basin, environmental conditions seem to affect significantly the life history parameters of this species. Therefore, the longevity of C.auratus seems to be rather limited by higher salinity in estuarine habitats and water temperature in wetlands.
The exponents of total length-somatic weight relationship of C.auratus, estimated in the wetlands, showed that the somatic weight grows allometrically with the total length. Differences between males and females in the TL–W relationship are explained by the differences in size distribution of the two sexes as a consequence of inter-sexual differences in growth, suggesting the convenience of using the appropriate estimate from those proposed for each group when calculating weights by sexes. The «b» values estimated in this study were different from those found by Kordjezi (1998) and Shoeiry (2001) in two neighboring estuaries (~60 km far from wetlands). In the estuary of Old Gorgan-Roud River it was 3.06 in females, 2.99 in males, and in the estuary of Qarasou River it was 3.17 in females, 2.96 in males. Geographic location and associated environmental conditions, such as salinity, stomach fullness, diseases and parasite loads, can also affect the value of «b» (Bagenal & Tesch 1978). Therefore; the differences in the «b» exponent between populations of C. auratus can be attributable to species plasticity and responses to different habitats.
Fitting the von Bertalanffy growth formula to observed lengths resulted in the estimation of higher values of maximum theoretical length than the maximum observed total lengths. Moreover, there were differences in these parameters between sexes and populations which can be attributed to differences in the size of the largest individuals sampled in each wetland. Considering an L¥ value 30 % higher than the maximum lengths observed (Garcia-Rodriguez et al., 2005), the obtained results are reliable values. A trade-off between growth rate (k) and maximum size (L¥) is often found. Optimum ecological conditions cause a shift towards larger maximum size. Comparison of k and L¥ from different populations in the south Caspian basin shows that the growth patterns were differen. These differences may be regarded as reasonable considering biological feature of the C. auratus in different habitats.
Calculated from published data of k and L¥, in different populations of the C.auratus from South Caspian basin f¢ ranges from 9.34 to 10.28 and from 9.13 to 9.5 in female and male respectively, indicating that the obtained f¢ of the C.auratus in both wetlands studied are very close to the reported findings from other localities (Kordjezi, 1998; Sayyad-Bourani et al., 2001). These evidences confirm the reliability of the C.auratus growth curve, as the overall growth performance has minimum variance within the same species because it is independent of growth rates.
In the wetlands of Alma-Gol and Ala-Gol, the overall sex ratio is unbalanced in favour of females, probably as a consequence of the gynogenesis even though the males had normally developing gonads. The observed sex ratio was unlike that found by Kordjezi (1998), Sayyad-Bourni et al. (2001) and Shoeiry (2001), proposed the M : F as 1 : 5.32, 1 : 148 and 1 : 5.02 in Qarasou river estuary, Anzali lagoon and Old Gorgan-Roud estuary respectively. The predominance of females is common in C.auratus populations. But in fact, it seems that the differences in sex are highly significant throughout its range distribution; wetlands have much more females than estuaries.
From maximum recorded GSI values, it is evident, that reproductive season of the C.auratus extends from February to April. Shoeiry (2001) and Sayyad-Bourani et al. (2001) also reported a similar situation; according to them, the spawning period of this species occurs slightly earlier, from January to March in Old Gorgan-Roud river and Anzali lagoon. In comparison with other cyprinid species, C.auratus has an extended breeding season (~3 months) in south Caspian basin. This extended breeding time of populations may be interpreted as an increase of reproductive effort which, in turn, promotes a rapid increase in the number and distribution of C.auratus as a successful invasive species.
In the studied localities (the present study & Shoeiry, 2001) C.auratus showed between-site differences in fecundity. Shoeiry (2001) reported that fecundity of a population inhabiting an estuary varied from 378 to 3865 with an average 1325±1009 eggs per female, which is more fewer than the findings of this study; 3165–13020 eggs per female in Alma-Gol and 3641–12980 eggs per female in Ala-Gol. These variations suggest a phenotypic response to sits-specific factors. Herrera and Fernandez-Delgado (1994) showed an existence of a trade-off between the energy devoted to reproduction and that devoted to maintenance or growth. Here (the present study & Shoeiry, 2001), the resulting trade-off can mean low energy is channeled into gonads and more devoted to maintenance in variable estuarine habitats where low fecundity observed.
Life history characteristics of the C. auratus is important with respect to management of the species, under consideration point to being simple, highly flexible fish, easily adapted to its habitat and gynogenesis, which, in turn, may be an adaptive response that promotes a rapid increase in the number and distribution of this species. As described above, it has been shown that the silver crucian carp life history parameters in south Caspian basin changed significantly over the its range distribution. These parameters varied with relative the environment to which they exposed. The variations relating to growth and reproduction may be interpreted as phenotypic plasticity and adaptation to local selective pressure. Bye (1984) suggested that in heterogeneous environments, successful species are the ones with the most phenotypic flexibility. The life history patterns of the C. auratus populations are in agreement with a strategy adopted for variable environments and suggest that populations are responding to environmental characteristics to improve fitness locally.
Zoocenosis — 2007
Біорізноманіття та роль тварин в екосистемах: Матеріали ІV Міжнародної наукової конференції. – Дніпропетровськ: Вид-во ДНУ, 2007. – С. 162-164.