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Summary Length–weight and length–length parameters were calculated in the Talkhehrud River, northwestern Iran, for four freshwater fish species belonging to two families. The b values varied between 2.27 and 3.19, with a mean ± SD of 2.2777 ± 0.387. The b parameter values in the length–weight relationship equations were determined as 2.73 for Alburnus atropatenae Berg, 1925; 3.19 for Alburnoides petrubanarescui Bogutskaya & Coad, 2009; 2.92 for Capoeta capoeta (Guldenstadt, 1773); and 2.27 for Oxynoemacheilus persa (Heckel, 1847). This study provides the first reference on the LWRs and LLRs for these species in the Talkhehrud River.

Summary Siah Mahi, Capoeta capoeta gracilis, is a predominant fish in the river systems of the south Caspian Sea basin. Although there is evidence of the geographical divergence of this taxon, no information is available on morphological differences within the subspecies populations. The study was designed to evaluate this differentiation in the Shirud River system of the south Caspian Sea basin in Iran. A total of 120 fish specimens (≥ 180 mm) were collected from the Shirud River; 33 morphometric and 10 meristic characteristics were recorded for each specimen. The standardized data were subjected to a principal component analysis (PCA) and variables with eigenvector ≥ 0.74 used as input for analysis of clustering, which grouped the 120 fish specimens into five distinct clusters. The overall random assignment of individuals into their original groups was high (86.7%), indicating that these specimens are highly divergent from each other. The proportion of individuals correctly classified into their original groups was 90, 81.8, 85.7, 100 and 76% for groups 1, 2, 3, 4 and 5, respectively. There were significant differences in nine morphometic characteristics among the five multivariate groups. Pectoral-anal length was the only characteristic that, based on all possible pair combinations of the five groups, could be individually distinguishable. With regard to meristic characteristics, a Kruskal–Wallis test showed that there were no significant differences among medians of the five multivariate groups.

Summary It is believed that streams of a basin may contribute to stream-specific variation in allometry coefficients related to between-habitat differences. To test intra-basin variation of the allometry coefficients of Lenkorn Capoeta capoeta gracilis (Keyserling, 1861), a total of 1731 individuals were sampled in six streams of the Gorganroud basin (southeast Caspian Sea) between April and May 2008. Values of b ranged from 2.647 for males of Chelchai to 2.964 for females of Madarsou, indicating negative allometric growth for the fish in the basin. There were variations in the allometry coefficient among the considered groups, which can be interpreted as species’ response to different habitats. To the best knowledge of the authors, this study documents the comparative reference on variation of allometry coefficient of Capoeta capoeta gracilis in southeast Caspian streams.

Capoeta capoeta capoeta (Gueldenstaedt, 1772), one of the subspecies of the genus Capoeta, is distributed throughout southwest, south and central Asia. This subspecies is a popular taxon in the south Caspian Sea basin of Iran (Abdoli, 2000). The reproductive biology of C. c. capoeta (Abdoli and Skandari, 1999) as well as some biological, ecological and parasitological characteristics of khramulya (C. c. gracilis) have been studied in the Madarso stream of Golestan National Park (Skandari, 1998). However, there is no published data on age and growth of C. c. capoeta in the southern Caspian Sea basin; the aim of present study was to investigate its age and growth characteristics from the Yasalegh stream in the Gorganrud basin. Specimens were caught by electroshocking with 200–300 V, 50 Hertz frequencies and one anode from the Yasalegh stream of the Gorganrud River in December 1997. This stream is situated in northern Iran (37 40¢N, 37 30¢E). The stream area where specimens were captured is about 40 m long and 5.5 m wide, with a depth of 26.5 cm. Water temperature was 11 C. Totalling 621 fish, specimens were preserved in 10% formalin in the laboratory, measured to the nearest mm, and weight determined with a digital balance to an accuracy of 0.01 g. Based on Bagenal (1978), scales were used for age determination of 263 specimens. Measurements were always taken from above the lateral line, below the anterior part of the dorsal fin. Each scale was cleaned with 5% KoH. The relation of weight to length was calculated applying the exponential regression equation W = aL, where W is the total weight, L the total length, and a and b the parameters to be estimated (Ricker, 1975). Length at age was modeled using three key parameters of the von Bertalanffy growth model (von Bertalanffy, 1938) described as Lt = L¥ (1)exp {-K [t-t0]}), where Lt is the length-at-age t, L¥ the maximum theoretical length, K the body growth coefficient synonym to the rate at which L¥ is attained, and t0 is the age of zero length fish (Ricker, 1975). The growth performance index (phi-prime index) u¢ was computed from the equation: u¢ = ln k + 2 · ln L¥ (Pauly and Munro, 1984). Of the total 621 fish examined, 403 were males and 218 females. The ratio of male to female was estimated as 1 : 0.54. The longest captured male and female fish were 179 mm and 225 mm, respectively.Maximumweight of males and females in the catcheswere 71.2 g and 119.4 g, respectively. Ages of the fish ranged from 0 to 3 years for both sexes (Fig. 1). von Bertalanffy growth equations were estimated as Lt = 190 (1)exp {)0.462 [t + 1]}) for males and Lt = 230 (1)exp {)0.472 [t + 0.742]}) for females. Females grew to a greater asymptotic length (L¥) and the rate at which this was achieved (K) was slightly lower than in themales. Length–weight relationship was calculated by using Ln weight = )11.754 + 3.052 Ln length for males and Ln weight = )11.753 + 3.050 Ln length for females. The slopes (b values) of the length–weight regression were not significantly different between sexes (ANCOVA, P < 0.001) (Fig. 2). The exponent (b) (b = 3.052, males; b = 3.050, females) indicated that weight growth of C. c. capoeta was isometric. The phi-prime ofC. c. capoeta in the Yasalegh stream was 9.71 for males and 10.11 for females. The sex ratio was different from those reported by Abdoli (1994), Hatami (1998) and Skandari (1998) (Table 1). The age structure of C. c. capoeta specimens caught in Yasalegh stream (0–3) differed from that observed in the Tilabad River (0–4)