Studies On The Biology And Population Ecology Of Glyptosternum Maculatum (Regan) In The Brahmaputra River, China

Glyptosternum maculatum(Regan) belongs to the genera of Glyptosternum,the family of Sisoridae,and the order of Siluriformes.G.maculatum is the only species of the genus distributed in the north side of Himalia mainly in the mid-reaches(from Bomi to Xietongmen) of the Yarlung Zangbo River and its tributaries.Specimens were collected with gill net from Yarlung Zangbo River branches,Lhasa River(H3000m) and Nyang Qu River(H2700m) in the years of 2004(May -September),2005(April～May),and 2006(March～June,October～November).The ecological and environmental monitoring of Yarlung Zangbo River was done bimonthly in 2005.Biology and population ecology of G.maculatum were studied.The main results are as follows:1.The age structure of G.maculatum populations is relatively complex which includes eleven age groups from three to thirteen.The individuals of the preponderant age groups were five to seven, occupying 79.03%of the total individuals.The total length range of the individuals was 115～320mm with an average of 193.41±36.15mm,and the body weight ranged from 16.3～373.7g with an average of 91.67±60.01g.However,the G.maculatum males showed greater total length and body weight than the females.2.Observed in reflected light,wide opaque zones and close translucent zones are arranged alternately on sectioned otollth,opercula and vertebra.The joints between the wide zones and close zones are the annulis.The interpretability of three kinds of ageing materials is as follows:vertebrae＞otoliths＞opercula.The index average percent error(IAPE) of otoliths versus vertebrae,otoliths versus opercula,and vertebrae versus opercula were 0.11%,0.17%,and 0.2%,respectively,showing good agreement with no significant difference between them(P＞0.05).Comparatively,however, vertebra is the best ageing material of the fish.3.Relationships between body weight(W) and total length(L) were described as follows: W_♀=5E-06L^3.142 and W_♂=5E-06L^3.1474,indicating isometric growth of G.maculatum.A power relationship between total length and the vertebrae radius was obtained for both sexes(♀,a=29.068 and v=97.173;♂,a=13A02 and v=107.88),von Bertalanffy parameters estimated from the back calculated sizes at age were L_∞=342.66mm,k=0.1142year^-1,to=0.7488year^-1 for females,and L_∞=460.24mm,k=0.0882year^-1,t₀=-0.2312 for males.The inflection point for the growth of female and male were 1.804 and 8.018 years,,respectively.4.The sex could be identified on the basis of the shape of genitalia.In the whole spawning stocks the minimum total length,body weight and age of the male individual at first maturity were 174.74mm,57.11g and 4 years,respectively,and those of the female individual were 164.78mm, 46.18g and 4 years,respectively.The gonadosomatic index(GSI) of ovaries and testises of adult G. maculatum suggests that this species has one peak of spawning activity in May.The mean diameter of mature eggs ranged from 2.3mm to 3.2mm,and it was significantly related to the length or GSI.The mean absolute fecundity was 727±407.83egg,and the mean relative fecundity was 43.26±20.65egg/cm body length and 11.79±5.31egg/g body weight.The absolute fecundity and relative fecundity increased with total length,body weight,age,and gonad weight.5.The gonad development of G.maculatum could be divided into 6 stages.The development of oocytes from phase 3 to phase 4 was synchronous.After reproduction,the ovary and testis change as they return back to stageâ…¡.The gonad of G.maculatum would develop slowly and remain at stageâ…¢, orâ…£throughout winter.Maturity of the gonad occurred only once per year.The male-to-female sex ratio in the population reaches its lowest level during the propagation period,and is higher during non-reproduction time than reproduction.6.G.maculatum feeds on fish,algae,organic debris,aquatic insects,protozoan,Copepoda, Oligochaeta,Cladocera,Rotifera,fish egg and gravel etc.Of the prey item categories used,fish and algae were the most important.The fish which G.maculatum mostly fed on included benthic species belonging to the Schizothoracinae or the genus Triplophysa.And attached diatoms were the algae most frequently seen in the alimentary canal of G.maculatum.The Shannon-Weaver diversity indices of the the prey items of G.maculatum changed with total length,and gonadic development stage,and habitat.The proportion of empty stomachs and fillness index didn't vary with total length,but did with gonadic development stage.7.The histological stuctures of the digestive system showed the adaptations of the digestive system in G.maculatum as a function of diet.Moreover,there existed a unique structure in G. maculatum,which were identified as a part of the liver named "exo-celiac liver".This new organ was located between skin and muscle and connected with the celiac liver by a funiform tissue,"joint belt". It had similar histological features and isozyme electrophoretogramic bands of lactate dehydrogenase, esterase,malate dehydrogenase and alcohol dehydrogenase with the celiac liver.8.The aquatic chemistry characteristcs and water quality of the water habitats where G. maculatum was distributed were also analyzed.Our results showed that dissolved oxygen was lower, both suspended substances and water temperature higher,and pH somewhat lower during wet season, and vice versa during dry season.Dissolved oxygen was higher in the Yarlung Zangbo River downstream and Niyang River,whereas pH and suspended substances were higher in the Yarlung Zangbo River middlestream.Water quality of the habitats of G.maculatum's except Laza,Nugeza and Yangzun rangedâ…¡according to the standards.The water,quality of the Yarlung Zangbo River downstream and Niyang River accorded with the standards for fishery while the pH and Cu content in the Yarlung Zangbo River up-and middle-stream,as well as suspended substances of all the Yarlung Zangbo River mainstream in July,were overrun. 9.The total mortality calculated from the length converted catch curve was 5.8737 year^-1 for female and 6.0096 year^-1 for male G.maculatum.Natural mortality was 0.7354 year^-1 for female and 0.6216 year^-1 for male,and fishing mortality was 5.1383 year^-1 for female and 5.388 year^-1 for male. Exploitation level of G.maculatum was 0.8748 year^-1 for female and 0.8966 year^-1 for male. Assessing the stock status using the B-H Model,we concluded that the resource of G.maculatum had already been overfished.To protect this resource,the fishing mortality coefficient must be reduced, and the first capture age should be put off by limiting the mesh.