Age, Growth And Reproduction Of The Roach Rutilus Rutilus (Linnaeus, 1758) In Ulungur Lake, Xinjiang, China

The present study was carried out in the Ulungur Lake (87°34'N, 46°52'-47°28'E), the second largest lake of Xinjiang and the ninth freshwater lake in China. The Ulungur Lake is an important commercial fisheries area of Xinjiang, the annual output every accounted for 50% of that in this region.Roach Rutilus rutilus (Linnaeus, 1758) is a small fish which mostly distributed in the European waters, and its only original distribution area in China is the Erqis River. It was transplanted to the Ulungur Lake in 1966, and its population was increasing rapidly since a channel was built between this lake and Erqis River in 1971 and become an important part of commercial fisheries whose catch ever exceeded 1400 t per year, 40 % of the total annual capture.However, a little but no thorough and continuous studies about the age, growth and reproduction of roach were carried out in Ulungur Lake, especially, in recent years the over-fishing, environmental changes and transplantation of fish were very serious. It's very important to find out these changes on the age, growth and reproduction of roach when accurate information is needed to develop population models for the conservation and management of this fish stocks. The aim of the present study was to describe the biological characteristics and compare them with that in 1990s, and provide the basic information for the conservation and management.The age, growth and reproduction of roach in the Ulungur Lake ware studied in 2555 samples obtained between November 2006 and July 2008. The maximum lengths observed were 224 mm (TL, total length), 113.4 g (W, weight) in males and 263 mm, 203.0 g in females, both in their seventh year of life (6+). The weight grew allometrically (b=3.3964 males; b=3.4606 females) with the total length and there were significant differences in growth patterns between males and females. The total length-weight relationship can be described by the following equations: W=1.0×10^-6TL^3.3964 and W=0.9×10^-6TL^3.4606 for males and females, respectively. Age determination based on otolith reading shows that the estimated ages are between 0+-6+ years old both for males and females. Growth could be described by von Bertalanffy equation with the growth parameters based on mean back-calculated total lengths: L_∞= 271.8202 mm, k = 0.1974 /y, t₀ = -0.6366 y for male and L_∞,= 300.8539 mm, k = 0.1819/y, t₀ = -0.8432 y for female, and weight growth parameters: W_∞= 186.0185 g,k=0.1966 /y, t₀ = -0.6450 y,φ= 9.5875 for male and (?) = 339.4707 g, k = 0.1819 /y, t₀ = -0.8239 y.φ= 9.7089 for female. The dominant age were 0+ and 1+. total·lengths were abundant in 65.0-110.0 mm in the samples obtained by Mihunzhens, and in the samples of Gillnets were 2+. 3+ and 4+, total length abundant in 150.0-210.0mm.The sex ratios were changed with the total length distribution. The whole sex ratio (1.4:1) was significantly different from 1:1 (p＜0.001). The first ages at maturity were 1 + for both sexes and by the age of 3+ all were 100% sexually mature. The smallest individuals at maturity for both sexes were: total length 104 mm, body weight 9.5 g for female with ovary weight 0.6 g and total length 87 mm. body weight 4.8 g for male with testis weight 0.2 g. The relationship between absolute fecundity and fish length (TL, mm) and weight (W, g) were described asF = 2.0×10^-4TL^3.3681(R²=0.82,n=78)and F = 165.87 W- 850.7 (R² = 0.88. n = 78).The growth rate and the reproduction investment of roach in Ulugur Lake have significantly decreased compared to that in the 1990s and the population shows a remarkable tendency for miniaturization of sizes and simplification of age structures. The main causes might be over-fishing. increasing salinity and content of SO₄^2- and Cl^- of water and the strengthening of interspecific competition for food. However, further researches should be made to find out the underlying correlation between the decrease of the growth reproductive investment of roach and these environmental factors.