The Research Of Biological Characteristics Of Anadromous Spawning Coilia Mystus In Estuary Of The Yangtze River

There are4species of Coilia in China. They are C. brachygnathu, C. grayii，C.mystus and C. nasus. C. mystus is one of the most important economic species in theYangtze River estuary，and migrates with short distance between river and sea in lateApril every year. The collection of C. mystus is the largest in the Yangtze River estuary.We collected samples in2012and2013, May to August, on north of the Grass Sandreservoir of Changxing island （31°27’N,121°44’ E） in the Yangtze River estuary,using Chongming local fishermen customary deep-water trawling nets （Length of themouth t is8m; Height is4m; Length of the net is15m;Mesh is1cm）.Time of everytrawling is about2h. This research studied the morphological characteristics, growthcharacteristics, propagation characteristics and consumption of energy during themigration. The main results obtained are as follows：1. Vertebra number of C. mystus inThe Yangtze river estuary was with range of65-69, averaged67; The dominant vertebra number was66-68; rib number was withrange of15–18,averaged16; Most individuals were16or17; Article anal fin numberwas between76and86, averaged81. The number of majority individuals were between79and84; Length of tail fin was between1.0and2.9cm, averaged1.8cm.2. Age structure of anadromous spawning groups of C. mystus in2012and2013was mainly age1and2, number of older individuals （age above3） was very small.There was no obvious relationship between otolith weight and age. In2012, lengthrange was8.2-17.5cm, the average was11.54±1.7cm, weight range was2.2-24.3g,average was7.49±4.12g;In2013, length range was4.2-21.3cm, the average was11.61±1.56cm, weight range was0.29to33.63g, average was6.83±3.19g; Femalelength and weight were generally larger than male,s. Body length had significant power function relationship with weight. Von Bertalanffy growth equation: Lt=20.94[1–e-0.47（t-+0.62）]、Wt=40.05[1–e-0.47（t+0.62）]3. In2012and2013,condition factor increasedgradually from the phase Ⅲto Ⅴ,the value is maximum in Ⅴ. The difference wassignificant between phaseⅢ、Ⅳ、Ⅴ、and Ⅵ（P≤0.01）.3. Spawning groups reach Yangtze estuary in may, and begin to lay eggs in earlyJune.Absolute fecundity was2081-21006,2107-24059grain respectively in2012and2013. Absolute fecundity and relative fecundity （FL） were power related with bodylength, and linearly related with weight; Relative fecundity （FW） fluctuated wavelywith length and weight. Developmentlal phase was above phase Ⅲ when they reachYangtze estuary. Gonad index gradually increased from the phase Ⅲ to Ⅴ. Phase Ⅵ,phase II were lower.Size of egg was554-1016μm, averaged787μm.4.77%of phase Ⅲ individuals,90%of phase Ⅳ, and all phase Ⅴ, Ⅵ hadnothing food in the stomach and gut. In contrast,93%of phase II individuals were atfullness of degree1and2, indicating that C. mystus fed nothing in the spawning periodand began to take food soon after spawning. The muscle fat content of femaleindividuals with phase Ⅲ oogenesis was only1.92%（wet-weight, bychloroform-methanol extraction, although ovary gathered62.43%of the total crude fatof the whole body. Thus, C. mystus allocated most energy to propagative organ, possiblythis is why small fish is difficult to spawning migration for long distance.In total, fatcontent in muscle and hepatopancreas decreased by12.5%and14.35%from phase Ⅲto Ⅵ respectively. Thereinto, fat content in muscle and hepatopancreas decreased by7.29%and3.65%from phase Ⅲ to Ⅳ respectively, in comparison with decrease of4.49%and8.63%from phase Ⅳ to Ⅴ respectively．This result suggests that thenutrition stored in the muscle mainly supplies for the migration and the earlymultiplication, while nutrition in hepatopancreas could boost energy supply for thesubsequent spawning process.