Study On Fish Early Resources At Honghu Section In The Middle Reaches Of The Yangtze River

The state-level natural protection areas for the white flag dolphin at Xinluo section of the Yangtze River in Hubei provides habitat sites?spawning ground?feeding areas for the dolphins and many kinds of major economic fishes such as Mylopharyngodon piceus ? Ctenopharyngodon idellus ? Hypophthalmichthys molitrix ? Aristichthy nobilis.The Honghu section of the middle Yangtze River is a important passage for migration fishes up to the spawning ground and a important passage for eggs and fish larvae drifting down to hatching?feeding?overwintering.A lot of researches on freshwater fish in the Yangtze River have been done,but investigate into fish early resource at Honghu section of the Yangtze River seem to be rare.Based on the Investigation on the fishery of early life history stage,we estimated eggs and fish larvae resources abundance,studied the species composition of fish early resources,analyzed the temporal and spatial variation pattern during early life history stage,compared the drifting density of fish early resources with the main environment factors.The sampling site was located in Yanwo Town,Honghu city,Hubei province.Through the investigation of two main breeding seasons from March to July 2014 and 2015 respectively,the main results were as follows:1 Large amount of different fish eggs and larvae flow through the sampling site at Yanwo Town from upper stream.A total of 2258 eggs and 3461251 fish larvae or juveniles were collected from March to July in two years.44 species belonging to 7 orders,14 families were identified.The numerically dominant species were members of Cyprinidae.Cyprinidae,Salangidae,Gobiidae,Serranidae,Bagridae,Cobitidae accounted for 97.27%,1.75%,0.54%,0.18%,0.10%?0.10%.Hemiculter bleekeri has the most number of all species,accounted for 90.40%,Parabramis pekinensis next accounted for 5.31%.The four Chinese major carp accounted for 0.89%.The other specie accounted below 0.10%.There were an estimated of 73.60×108 ind.and 1127.5×108 ind.fish larvae drifting through the sampling site in 2014,while were 37.27×108 ind.and 1604.79×108 ind.fish larvae.2 In 2014 and 2015,an estimated 2.05×108 ind.eggs of the four Chinese major carp and 1127.5×108 ind.fish larvae drifting through the sampling site during the major breeding season.Mylopharyngodon piceus ? Ctenopharyngodon idellus ? Hypophthalmichthys molitrix ?Aristichthy nobilis accounted for 4.7%?20.97%?74.32%?0.64% of the whole four Chinese major carp.Compared with other Investigations in history,the proportion among the four Chinese major carp change a lot.The number of Hypophthalmichthys molitrix Marked rise,the other three species decreased.Combined with the having been hatchted time of eggs and the water velocity when sampled,we got the four Chinese major carp eggs coming from 12-135 km upstream of the collecting site in 2014.In the range,Yanwo-Longkou ? Chibi-Nanmen Zhou ?Lucheng-Yongji?ChenglingJi-Dawang were estimated as the spawning ground of the four Chinese major carp.In 2015,the eggs were from 83-161 km upstream of the collecting site and the spawning ground of the four Chinese major carp were Nanmen Zhou-Honghu?Lucheng?ChenglingJi-Dawang.3 In 2014 and 2015,the water discharge and the water level both had a rising trend;the water temperature is all above 18? and higher with the sampling date.The water transparency data is low,All the data is no more than 55 cm.Dissolved oxygen turn between 5-9 mg/L which satisfying most of fish to live.From May to July,Dissolved oxygen decreased Gradually with the sampling date.pH turn between 6.94-8.10.we can draw a Conclusion that the reproduction activity of most fish species was affected by some environmental factors obviously.RDA analysis and Pearson rank correlation shows that the fish larvae drifting density of Hypophthalmichthys molitrix ?Ctenopharyngodon idellus ? Mylopharyngodon piceus ? Parabramis pekinensis ?Parabotia fasciata?Leptobotia purpurea et al.was positively correlated with diurnal variation of water discharge?water level?water temperature?water transparency ?pH and was negative correlation with dissolved oxygen.The fish larvae drifting density of Hemiculter bleekeri?Pseudolaubuca sinensis?Rhodeus sinensis et al.were also effected by the major environmental factors but it is not so significant.4 The result of diel sampling on June 8th to 9th?June 23 th to 24 th and July 4th to 5th indicated that the fish larvae has a higher density in the span of 18:00 to 4:00 the next day.and a lower density in the span of 6:00-18:00.Hemiculter bleekeri?Parabramis pekinensis?Rhinogobius giurinus,have a highest density in the span of 20:00-22:00.the peak of the Hypophthalmichthys molitrix density is 20:00-4:00 the next day,while Neosalanx taihuensis is 0:00-6:00.