Study On Age Growth,reproduction And Skeletal Differences Between Schizothorax Pseudaksaiensis And Other Two Species

Schizothorax pseudaksaiensis（Herzenstein 1889）,belonging to Cypriniformes,Cyprinidae,Schizothoracinae,Schizothorax,Schizopyge,place name,Yellow croaker,fine scale fish.Typical cold-water indigenous rare fish,one of the main economic fish,the current distribution area has shrunk sharply,and only a small amount is concentrated in the upper reaches of the Yili River and its main stream.It has been listed as the second-level key protected aquatic species in Xinjiang Uygur Autonomous Region in 2022wild animals（Xinjiang Uygur Autonomous Region List of Key Protected Wild Animals Xinzhengfa[2022]No.75）.Taking S.pseudaksaiensis as the main research object,through continuous annual sampling,research on its morphological characteristics,age growth,reproductive biology and skeleton comparison,which has theoretical and practical significance for maintaining population dynamics and fishery ecological balance;Further clarify the taxonomic status and interspecific differences of Schizothorax,enrich the taxonomic basis of the three Schizothorax species,consolidate the taxonomic basis of aquatic vertebrates,and provide a scientific basis for the protection of plateau fishery germplasm resources.The main results are as follows:1 Morphological characteristicsThe body of S.pseudaksaiensis is elongated,slightly flattened laterally,with a round abdomen,complete lateral line,and gluteal scales;the head is conical,and the top is slightly wider;the snout is pointed,the mouth is inferior,arc-shaped or slightly horseshoe-shaped,the upper jaw is longer than the lower jaw,and the lower jaw is longer than the lower jaw.Front edge without sharp horny;2 pairs of whiskers,equal in length.Dorsal fin typeⅢ,6～8,anal fin typeⅢ,5,pectoral fin typeⅠ,15～18,pelvic fin typeⅠ,8;3rd dorsal fin with well-developed spines,serrated trailing edge,longer than 1st and 2nd dorsal fin spines and dorsal fin Strips;dorsal rostrum distance slightly longer or slightly shorter than or equal to dorsal-tail distance;pelvic fin origin is opposite to dorsal fin origin.Among the 10 measurable traits,body height is greater than body width,and tail peduncle length is greater than tail peduncle height.Among the ratios of measurable traits,the variation range of body length/eye diameter is the largest,and the variation range of body height/body width is the smallest.Combined with its frame structure diagram,it can be seen that the body of S.pseudaksaiensis is elongated and flattened,showing a spindle shape;the tail peduncle is longer than the tail peduncle height,and the head and eye diameter are smaller.2 Age growthThere are three pairs of otoliths of S.pseudaksaiensis.The morphology of the lapillus otoliths are large and nearly square,thicker in the middle,gradually thinner toward the outer edge,and there are obvious protrusions in the center of the outer surface.The back of the otolith is wavy,and the edge of the abdomen is shallowly curved;the basal lobe is underdeveloped;the main intersulcus is not obvious.The morphology of otoliths is related to the higher altitude and lower habitat temperature.The lapillus otoliths,vertebrae and gluteal scales all present typical annual ring characteristics with alternating broad and narrow bands,and their age range is determined to be 1 to 23 years old through three age identification materials.The total body length of the fish ranged from 47.30 mm to 538.60 mm,and the age range was from 1to 23 years;The female body length ranged from 49.04 to 538.60 mm,and the age range was from 1 to 23years old;The male body length ranges from 47.30 mm to 458.39 mm,and the age ranges from 1 to 19years old.Carry out the body length and weight correlation fitting of S.pseudaksaiensis overall and male and female populations,compare the relationship between b value and 3,and determine that it is a uniform growth fish.The relationship between body length and body weight is:overall population:W_total=8.48×10^-6L^3.1095;female population:W_female=1.28×10^-5L^3.0436;male population:W_male=1.73×10^-5L^2.9759.The von Bertalanffy growth equation is:emale population:L_t=737.7052(1-e^{-0.0487（t+05887）}),W_t=6853.2756(1-e^{-0.0487（t+0.5887）})^3.0436;male population:L_t=669.9625(1-e^{-0.0548（t+0.3609）}),W_t=4447.2318(1-e^{-0.0548（t+0.3609）})^2.9759.The inflection point ages of the female fish and male fish were 22.28 and 19.55years old,respectively.3 Reproductive BiologyThe sex ratio of S.pseudaksaiensis was 0.89:1,and the peaking reproductive period was from May to June.The mature egg was light yellow,the egg diameter was about（2.510±0.004）mm,and the yolk volume accounted for about 3/5 of the egg.According to the egg size distribution and gonad maturation index（GSI）,it is speculated that it belongs to the type of synchronous spawning.Based on the fecundity of female fish in stages IV～Ⅴ,the absolute fecundity（F）is 55652.01±25468.78 grains/tail,ranging from14500.00 to 112636.26 grains/tail;the relative fecundity（RF）is 25.92±10.69 grains/g,ranging from3.71～47.63 grains/g;there was a linear correlation between absolute fertility,body length and body weight,and the fitting equations were:F_L=624.14L-256868.74（R²=0.9615）,F_W=35.80W-24149.19（R²=0.9113）,respectively.The formation of its reproductive characteristics reflects the adaptability of S.pseudaksaiensis to the habitat environment,which is not only related to its own characteristics,but affected by the environment and nutritional status.The mature eggs of S.pseudaksaiensis were settling and slight viscosity in water.After 30 min of fertilization,the periovum space was the largest and the egg diameter was about（2.800±0.005）mm.At a water temperature of（15.5-17.5）°C,the fertilized eggs hatched for 112.14 h,and the required accumulated temperature was about 1924.893°C h;the newly hatched larvae were（8.721±1.276）mm long,with heartbeat and blood circulation,and lay still for most of the time underwater,there is occasional movement,and it takes time to complete the developmental stages of fertilization,cleavage,blastula,gastrula,neurula,organ formation and hatching.Early larval development is divided into four stages:eye pigmentation period,body pigmentation period,swim bladder inflation period,and yolk-sac complete absorption period.The yolk-sac is completely absorbed 432 hours after membrane emergence,and the total length of larvae is（14.712±0.036）mm.The relationship between the total length of larvae（L_T）and the days after emergence（D）:L_T=0.500D+6.949;the relationship between the total length of yolk sac（L_Y）and the days after emergence（D）:L_Y=-0.127D²+5.982;Larval length（L_T）and yolk sac volume（L_P）relationship:L_T=-1.900L_P+12.525;Yolk sac length（L_Y）and yolk sac volume（L_P）relationship:L_Y=0.801L_P+4.325;The relationship between yolk sac volume（L_P）and days after membrane emergence（D）:L_P=0.004D²-0.237D+2.435.4 Comparison of skeletal differences with two other Schizothorax speciesThe three species of Schizothorax lived in high salinity and cold water,and had their unique characteristics of bone evolution.In addition to the obvious difference in the number of bone fragments,some bones also have obvious changes in shape:such as lateral ethmoid bone,frontal bone,pterygoid bone,parasphenoid bone,parietal bone,upper ear bone,upper occipital bone,sphenoid bone,Differences are shown in the premaxilla,pterygium,middle pterygium,pharyngeal bone,operculum,and coracoid,especially in the lateral ethmoid,parietal,superior occipital,sphenoid,pterygoid,and hypopharyngeal bones.In addition,the pharyngeal teeth and the pharyngeal bone connected with the pharyngeal teeth of S.pseudaksaiensis and Schizothorax eurystomus are more robust than those of Schizothorax biddulphi.The number of vertebrae of S.pseudaksaiensis is 4+44-45+1,and the number of vertebrae of S.eurystomus and S.biddulphi is 4+42-43+1.