Studies On Biology And Restoration Of Spawning Grounds For Anabarilius Grahami In Fuxian Lake

The Anabarilius grahami was the exclusive fish to Fuxian Lake in Yunnan Province,China.In recent years,its population has been greatly reduced and once endangered due to the invasion of exotic species,overfishing and degradation of spawning grounds.To better recover and conserve the population resources of this fish,433 fish were collected in Fuxian Lake from October 2021 to July 2022.Through the study of the growth,reproduction and feeding characteristics of the fish,the biological adaptive strategies of the fish in adapting to environmental stress and the reasons for the slow recovery of the fish population were analyzed.At the same time,the existing spawning grounds and the ecological conditions required for spawning were investigated by means of early resource surveys.On this basis,ecological restoration of historically damaged spawning grounds was carried out using artificial excavation,and the feasibility of spawning ground restoration was explored.The main findings were as follows:1.The body length range of the collected female fish was 10.6-22.5 cm,and the dominant body length was 11.0-14.0 cm,accounting for 84.4%,and the age structure consisted of age 2-8,with the dominant age being age 2-3,accounting for 96.7%;the body length range of the male fish was 10.0-17.3 cm,and the dominant body length was11.0-13.0 cm,accounting for 71.4%.The age structure of males ranged from age 2 to 7,and the dominant age was age 2,accounting for 88.6%.The variation in fullness of Anabarilius grahami varied significantly（p<0.05）with body length and season.The fitted body length-weight relationships for Anabarilius grahami were:female:W=0.00342SL^3.399,male:W=0.00976SL^3.014,undiscerned:W=0.00325SL^3.220,with uniform growth for males and positive anisotropic growth for females and sex undiscerned.The V-B growth equations for length and body weight of Anabarilius grahami were:females:L_t=31.05(1-e^{-0.1245（t+2.1062）}),W_t=443.72(1-e^{-0.1245（t+2.1062）})^3.399;males:L_t=23.98(1-e^{-0.2447（t+0.8032）}),W_t=151.65(1-e^{-0.2447（t+0.8032）})^3.014,with k values of 0.1245 and 0.2447 for female and male Anabarilius grahami,respectively,which are slow-growing fish.The inflection point ages for females and males were 7.7 and 3.7 years of age,respectively,when the corresponding body length and weight were 21.91 cm,135.76 g and 16.02 cm,44.99 g,respectively;2.The male to female ratio of the Anabarilius grahami population was 1.11:1,increasing with length from 100 to 150 mm,and decreasing with length from 150 to 180mm;the distribution of the IV egg diameter of Anabarilius grahami ranged from 0.91 to1.22 mm,and the frequency distribution of egg diameter was unimodal in all five months.The frequency of egg size distribution was unimodal in all five months,and the gonadal sections showed that the eggs of the fish were developing synchronously,so the fish belonged to the once-a-year spawning type.The reproductive season of Anabarilius grahami was from late February to early July,with the main reproductive season being from March to May,accounting for 82.4%of the total spawning population,which was consistent with the monthly variation in gonadal development.The absolute fecundity of Anabarilius grahami ranged from 1634 to 13306 grains,with a mean absolute fecundity of 4825±2567 grains;the relative fecundity ranged from 110 to 269 grains/g,with a mean relative fecundity of 183±38 grains/g;the absolute fecundity of Anabarilius grahami was significantly linearly related to body length（SL）,body weight（W）,ovarian weight（OW）and age（A）,and the best-fit equation were:F=139.44SL²-2585.70SL+14342,F=144.61W^1.07,F=925.48OW+538.51,F=380.03A²+1117.9A-234.05;the initial sexual maturity body length and age were 10.05 cm and 1.91 years for female and 9.59 cm and1.55 years for male Anabarilius grahami,respectively.3.The food composition of the Anabarilius grahami was analyzed by different indices.In terms of the number percentage（N%）,algae accounted for the highest percentage（99.99%）of the food composition of the Anabarilius grahami,with the highest percentage of the Chlorophyta（55.13%）dominated by Spirogyra sp and Ulothrix sp algae,accounting for 29.63%and 14.98%,respectively.In terms of the relative importance index percentage（IRI%）,the Anabarilius grahami most important food items for whitefish were Coleoptera（36.57%）,followed by Limnodrilus hoffmeisteri（18.65%）,Cyclotella sp（13.08%）and Spirogyra sp（9.56%）,in addition to a small amount of Neosalanx taihuensis and fish scales.The results of Amundsen’s graphical method showed that the Anabarilius grahami was generalist fish,with the occurrence rate of Coleoptera（56.82%）and prey-specific abundance（77.45%）were relatively high among all food items,which were the main food items for the Anabarilius grahami.Limnodrilus hoffmeisteri and Daphnia were the relative most important foods,which occurrence rate and abundance of prey-specific abundance were 43.18%,55.93%and 38.64%,22.54%for Daphnia magna,respectively.Although the occurrence rate of algae was high,the prey-specific abundance was not high,which may be incidental intake of main food.The results of feeding strategy showed that there were large differences in the intake of rare or unimportant baits among different individual Anabarilius grahami,while there was more food overlap among individuals for the main baits,Sphingomonas and Hoffmania.4.From 2021 to 2022,282 eggs and 327 juvenile fish were collected in Fuxian Lake,and 13 species of fish were identified,of which Cyprinidae accounted for the most,75%,and Hemiramphidae,Eleotridae,Gobiida,and Bagridae for one species each.The spawning grounds of the Anabarilius grahami are mainly located in caves with flowing water in Ming Xing and Lu Chong,where spawning occurs more than 50 times a year;the spawning grounds in the coastal zone of Da Wan,Xiao Wan and Gu Dao are shallow areas with wind and wave lapping,where the instantaneous flow velocity can reach 0.1～0.3 m/s during spawning and there are a large number of smooth gravels in the area,where spawning occurs 3～5 times a year.The number of spawning grounds has decreased by54.5%compared to the historical period,and the spawning activity has become more dependent on the gullies,and the breeding pattern of"For three days to seven days"has changed.The spawning activity of Anabarilius grahami occurred between 16:00 and22:00,with a peak of 83.67%entering the spawning ground between 16:00 and 20:00,which was significantly correlated with the daily variation of water temperature and DO in the lake environment（P<0.05）.The suitable range of water temperature for spawning is 17.3～25.7℃,flow rate is 0.1～0.4 m/s,dissolved oxygen is 1.68～6.02 mg/L,salinity is0.12～0.19 ppt,and p H is 8.36～9.22.From a comprehensive point of view,Anabarilius grahami have high requirements for spawning environment,prefer water The fish are very demanding in terms of spawning environment and prefer a weakly alkaline environment with fresh water and a certain flow rate.5.During the 31-day period from May 12 to June 12,2022,11 spawning events occurred in the restored spawning grounds with 226 spawning aggregations,and 20spawning events occurred in the spawning grounds with intact habitat with 223 spawning aggregations.In general,There were significant differences in spawning times between restored spawning ground and intact spawning ground（P<0.05）,but in terms of spawning population number,the difference between the two groups was not significant.A comparison of the effects of the three different spawning substrates showed that the average individual egg attachment rates were 3.32,1.31 and 0.47 eggs/cm²for palm,gravel and Pteridium revolutum Nakai,respectively,and the average individual egg attachment rates per unit area were 78.49%,32.78%and 9.46%,respectively.Overall,palm materials are more suitable for repairing the attachment base of the natural habitat of the fish spawning grounds.