Study On The Estimation Of Enhancement Silver Carp And Bighead Carp Populations And Quantification Their Food Cunsumption On Algae In Ge Lake

Stock enhancement is an important method of restoring aquatic biological resources,adjusting fishery structure and improving the aquatic ecological environment in China.And assessing of release effect also plays an important role to promote the ifishery policy,ensure the effectiveness of stock enhancement,and truly protection of the aquatic ecosystem.However,there is no standardized method for assessing the effect of stock enhancement.Which will inevitably restrict the development of the work.Since the beginning of this century,Ge Lake has been confronted with problems such as degradation of waterweeds,accumulation of pollutants and decline of fishery resources.The Gehu Fishery Management Committee of Jiangsu province began to release silver carp and bighead carp on a large scale in 2013 to increase fishery resources,reduce algae in lakes and restore the ecological environment of lake.This dissertation evaluates the actual application effect of enhancement of silver carp and bighead carp in Ge Lake through their living conditions and algae feeding.1.Research investigated the population age structure and growth of released silver carp and bighead carp in Ge Lake in 2017.The results showed that the age composition of silver carp were 1-4 years old,of which 1 and 2 years old fish account for 90.3%;bighead carp age composition is 1-5 years old(only 1 fish in 5 years old),and 2-4 years old fish account for 90.5%.The average body length and body weight of 1-year-old silver carp in Ge Lake were higher than those of Gehu bighead carp,but average body length and body weight of bighead carp in Ge Lake were higher than those of silver carp in later years,and 2-year-old bighead carp was significantly higher than 2-year-old silver carp.Chi-square test was carried out on the Von Bertalanffy growth equation of silver carp and bighead carp and found no difference between the theoretical and the practical.The growth rate K of silver carp is 0.2755,the progressive body length L?= 82.6189 cm,and the progressive body weight W?= 11937.02 g.The growth rate K of silver carp is 0.1403,the progressive body length L?= 124.3732 cm,and the progressive body weight W?= 33794.2 g.Growth velocity and acceleration of silver carp and bighead carp in Ge Lake were obtained by derivation of growth equations.The turning point age of silver carp and bighead carp in Ge Lake was 3.15and 6.38 respectively.By comparing the growth of silver carp and bighead carp in Ge Lake with other lakes,it was found that the released populations of silver carp and bighead carp in Ge Lake had not reached the maximum stocking capacity,and could still increase the population resources.2.Based on the biology parameters of silver carp and bighead carp in Ge Lake,the mortality rate of silver carp and bighead carp were assessed by catches model and length virtual population analysis.Results showed that the natural death coefficient of silver carp was 0.38,the fishing death coefficient was 0.05 and the total death coefficient was 0.43.The natural death coefficient of bighead carp in Ge Lake was 0.22,the fishing death coefficient was 0.03 and the total death coefficient was 0.25.Catches data showed that the resource of silver carp in Ge Lake was 14.32 million in 2017 before catching,and the surviving of this group was 9.14 million by the end of 2017.The resource of bighead carp in Ge Lake was 13.59 million in 2017 before catching,and the surviving of this group was 10.58 million by the end of 2017.Based on 2 cm interval in FISAT II software,the resources of silver carp in Ge Lake were 13.90 million before the start of fishing in 2017 and 11.38 million before the start of fishing in Ge Lake in 2017.The results are similar and can be considered to be more credible.In addition,although the catching age has been reached since the beginning of the release,most of the deaths of smaller individual fish are still natural deaths.With the increasing of fish body length,the natural mortality rate of the two species decreased,and the fishing mortality rate continued to rise.3.On the basis of assessing the abundance of silver carp and bighead carp in Ge Lake,we use the environmental DNA investigated the distribution of silver carp and bighead carp.Two pairs of universal primers were designed for e DNA,and tested by fish samples and environmental samples.The results showed that 16 S 400 primers could amplified common fish,but the environmental samples.16 S 200 primers had better amplification effect on environmental samples and could be used in the next experimental material.The temporal and spatial distribution of silver carp and bighead carp in Ge Lake was evaluated by the high throughput sequencing and quantitative PCR.The results showed that silver carp in Ge Lake were more abundant than bighead carp.Most of the samples of silver carp and bighead carp were found in the whole lake in 2017.Whereas in 18 years both fish concentrated in the north and the middle of Ge Lake.4.The daily feed of silver carp and bighead carp in Ge Lake was studied by 24-hour continuous algae monitoring experiment.The feeding habits of silver carp and bighead carp were analyzed by microscopic.The results showed that bighead carp in Ge Lake mainly feed on zooplankton and mainly on cladocera,but in summer and winter,phytoplankton biomass were more abundance.Silver carp feeds mainly on phytoplankton and mainly on diatomaceae throughout the year.Diatoma is the main food resource of silver carp and bighead carp in Ge Lake.The feeding rhythm of silver carp and bighead carp in Ge Lake was studied according to the feeding intensity in 24 h experiment.The results showed that the feeding intensity of silver carp and bighead carp in Ge Lake was different in different seasons.The feeding quantity of silver carp in Ge Lake was the highest in autumn and the lowest in winter,while that of bighead carp in Ge Lake was the highest in spring and the lowest in winter.The feeding peaks of silver carp in spring and autumn all appeared at 2:00 and bighead carp in spring and autumn at 14:00 in Ge Lake.The daily feed of silver carp and bighead carp in Ge Lake was estimated by Elliott and Psrsson model and Eggers model.The results of the two models were similar.According to the analysis of food intake,silver carp in can eat 8 times its body weight alage per year,and bighead carp in Ge Lake can eat 1 times its body weight alage per year.The results showed that it is feasible to use silver carp and bighead carp to control algae in lakes.5.A dynamic model which according to the deduction process of BevertonHolt model and the fishery management policy of Ge Lake,was established to monitor the population dynamics of silver carp and bighead carp population in Ge Lake,and put forward a formula of algae intake by silver carp and bighead carp.The use of the model needs to meet certain conditions.Firstly,the model does not consider the migration of fish(including immigration and emigration),and is only suitable for the closed water bodies.Secondly,the released fish can not reproduce themselves in water,and the increase of their population can only be achieved through enhancement.Thirdly,the release time and assessment time of fish are integral times of half a year.Fourthly,fish enter the captured population in the year of release.Fifthly,the mortality rate of the whole released fish can be represented by the average mortality rate.