Length–weight relationships of Capoeta capoeta capoeta (Gueldenstaedt, 1772) in the Gorganrud River, south Caspian Basin

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)