A Study On Age, Growth And Reproduction Of Northern Pike (Esox Lucius L.,1758) In Ulungur Lake

Northern pike was an important piscivores fish across the northern hemisphere which mostly distributed in the Eurasian and North America, and its only original distribution area in China was the Erqis River. It was migrated to the Ulungur Lake in 1966, and became one of the most important comemercial fisheres now whose catch ever exceeded 800 t per year,20% of the total annul capture of the lake.It palyed a significant role in maintaining the balance of fish community structure. It was beneficial to conservation and exploitation of this resource to understand their biological characteristics. Field observations were carried out during January 2007 to August 2008, with a total of 461 specimen collected.Six kinds of calcified structures were compared by using interpretability, agreement and CV (Coefficient of Variation). It was demonstrated that the sectioned sagittas was the best structure for ageing northern pike with the highest interpretability (100%) and the highest agreement(>99%) at ages between two times age readings by the same reader, and no false annuli was found on sagittas. Scales were also recommended for age determination for its good agreement and lowest age bias with sectioned sagittas, though the interpretability was slightly lower. However, ages at higher age classes (≥5) would be underestimated by readings on scales. Ages determined from opercular bones, vertebraes, metapterygoid bones and cleithrum of northern pike almost agree with that from sectioned sagittas at age 1 and 2, but significantly lower after age 2. It was suggested that the four structures were not appropriate for ageing northern pike. The maximum theoretical length value calculated from scales was 1523.2 mm, which was obviously higher than that value calculated from sectioned sagittas (1202.5mm). The possible reason was that annuli were lost on scales in older northern pike and the growth rate was over estimated.The ages of male northern pike sample were 1 to 4 years old, and 1 to 5 for females. Only 1.3% was above 4 years old. The dominant total length class was 300-600mm, and the average total length was 455.8 mm (n=461). The whole sample was composed of 258 females and 189 males. The average TL for females was 487.9 mm, and 416.6 mm for males. The back-calculated TL for females at ages were higher than males. There was no significant difference in the total length-weight relationship between males and females. The combined equation for the total length-weight relationship was:W=2.0×10-6TL3.1641 (R2=0.99, n=461). The von Bertalanffy equation for the population was: TLt=1202.492[1-e-0.194(t+0086)]. The growth parameters obtained from the von Bertalanffy equation were:Φ=3.45, (0=23.3.The first ages at maturity were 1 year for both sexes. By the age of 2 were 100% sexually mature for male, and age 4 were 100% sexually mature for female. The smallest individuals at maturity for both seses were:total length 287 mm, body weight 116.3 g for female with ovary weight 0.37 g and total length 277 mm, body weight 117.0 g for male with testis weight 0.1 g. The relationship between total length (TL) and the proportion of adult males and females was calculated as P♀=1/[1+e(12534+00327TL)]and P♀=1/[1+e(7134+0128TL)], respectively. From this, the estimated size for 50% sexual maturity size (TL50) was 38.3 cm and 55.7 cm in males and females, respectively. The range in egg diameter recorded was 1.4 mm to 2.5 mm, and mean egg diameter of which was estimated as 1.98 mm, and most of which were 1.9-2.1 mm (58.1%). The absolute fecundity ranged from 120-125832 with a mean of 37354.4. The relative fecundity ranged from 1.0-148.6 eggs g-1 with a mean of 19.4 eggs g-1, and 4.2-1603.0 eggs g-1 with a mean of 526.5 eggs g-1. The relationship between absolute fecundity and fish length (TL, cm) and weight (W,g) were described as:F=20.878W-2923.6 (R2=0.7201, n=63)F=2.5×10-3TL3.8972 (R2=0.7349, n=63)...