Physio-ecology Of Northern Sheatfish Silurus Soldatovi During Early Development

Northern Sheatfish (Silurus soldatovi),is freshwater sarcophagic fish with the gigantic body under the catfish family, Siluriformes order. They are naturally distributed in Heilongjiang river system and middle to bottom of Liaohe river system in northern China. Because of narrow distribution and low population, this species is being in imminent danger and is listed in red data book. They are not only valuable in natural ecology system and variety of aquatic animal, but also important in aspects of genetic and evolution. As the natural food compare to red meats for human, Sheatfish is high in protein, tasty as seafood, and beneficial to farm. The fast growth and durable to cold water temperature are the positive traits and bring scientist's attention that experts had already successfully hatched eggs to fries and reared in ponds. Its prospective economic value will be increased as the natural population climbed and proper monitored and controlled.The biggest obstacles for artificial hatching and early fries rearing are the high mortalities and fighting and killing each other. The survival rates are relatively low which affect the increasing rate of population. To find the solution of this problem, a serial of researches were undertaken in our laboratory, the results showed:1. morphology and structure of egg chorion and role on embryonic development of northern sheatfishThe surface ultrastructure of mature egg chorion of the tame northern sheatfish from Heilongjiang river was investigated by scanning electron microscopy. The outermost layer was composed of a thin lamella with a jelly coat. The surface of jelly coat was characterized by a overlapping net-like fibrillar lamellae, many clefts with bridges and pores. The pore canals were 0.25μm in diameter. The pore density was about 0.7-1.Oμm-2. The pores on the surface of jelly coat were distributed uniformly. Mature egg of sheatfish possessed a funnel-shaped micropyle at the animal polar region. The area surrounding the micropylar was about 0.04 mm2 in diameter with 3-8 ridges in radial arrangement. Fertilized eggs in which jelly coats were removed mechanically presented no adhesiveness and exhibited inlays of irregular granules on their surface. The relationships between surface structure and functions of egg chorine were discussed.2. Observation of tissues and organs of nutrition system during postembryonic early development of northern sheatfishUsing ultrastructural and tissue serial section techniques, postembryonic development of liver, pancreas and yolk absorption of northern sheatfish were observed. The results showed that larvae in about 2d after hatching in the heart behind a liver cell mass, gastrointestinal opened, it started to eat; in 3d liver cells gradually increased; in 4d liver lobulation. With the growth of larvae liver, pancreas development degree is also different. Pancreas development in 7d approximate adult. After hatching.4d after hatching yolk were all absorbed, liver volume increased, while there were simple intra-abdominal stomach and intestinal organs, the formation of the liver, stomach, intestine shape. The development of liver with yolk sac absorption closely related. In 8d larval external nutrition mechanism has been developed. In 16d liver tissue close adult. Feeding and sensory organ development with larval nutritional physiology function mutual adaptation, visual development early, formation time of chemical receptors such as taste, touch and jaw tooth basically the same.3. Digestive physiology and digestive enzyme properties of northern sheatfish(1) The activities of some digestive enzymes and alkaline phosphatase were investigated during the larval development of northern sheatfish Silurus soldatovi for 1-10 days age. The result indicated:the larva (about 2 days after hatch) of northern sheatfish had the upper activities of the alkaline protease and the alkaline protease activities achieved the peak value in the 5 days old, subsequently, the alkaline protease activity begined to decline; a low value of 8 days old again. The overall change was an upward trend. The acid Protease activity in the 1-8 days age was at a low level, increased rapidly after 8 days age. The amylase activity in the five-day-old reached the highest value, and after then began to decline to a lower level; the lipase activity changed large and showed two peaks appeared at 3-4 and 6-8 days old. The digestive enzyme activity and alkaline phosphatase activity of larva in feeding animal feed were higher than those feeding artificial feed. Throughout the early development process, the alkaline protease activity was higher than the acid protease, alkaline protease and amylase specific activity had decreased significantly in about 8 days old larvae of transition, while the acid protease activity began to increase rapidly, which indicated that the changes of digestive enzymes activity had relevant with digestive function converting during the development of fish larvae. Alkaline phosphatase activity had upward trend within the 10 days old, which indicated that the northern sheatfish gastrointestinal function had improved gradually.(2) Effects of temperature and pH value on the protease and amylase activities in stomach and intestinal canal were studied on average body weight 80.2±3.5g and average body length 19.4±1.7 cm of northern sheatfish. The protease activity was affected by pH value very observably. The optimum pH value of stomach protease was about 2.6,the optimum range was 2-3,the relative activity was 67.65±8.99 U/mg protein; The optimum pH value of intestinal canal for protease was 9.8-10.3, the relative activity was about 149.22±11.33 U/mg protein. The optimum pH value of stomach and intestinal canal for amylase were 6.0 and 6.5-7.0, the later relative activities were about 3 times of the former. The enzymatic activity affected by temperature was very observably too. The optimum temperature of stomach and Intestinal Canal for protease were 35℃and 40-45℃; the relative activities were 78.88±6.80 and 192.26±17.22 U/mg protein. The optimum temperature of stomach and intestinal canal for amylase were 45℃and 40-45℃, the relative activities were 11.77±1.98 and 16.52±1.62 U/mg protein. In the paper, the enzymatic activity of northern sheatfish was compared with other carnivores and herbivores.(3) The effect of feeding on the activity of protease,amylase and lipase in the main digestive organs of northern sheatfish was studied. The results showed that the activity of protease in stomach decreased after feeding, then increased and kept at a high level after 3h of feeding,which was 126.40±18.96 U/mg protein and presented a striking contrast to pre-feeding (P<0.05).But the activity of protease in intestinal canal increased all along and kept at a higher level after 4h of feeding, which was 70.68±9.87 U/mg protein. The effect of feeding on the activity of amylase indicated that the amylase in stomach decreased after 1h of feeding (P<0.05),then increased and kept at a higher level after 3h of feeding, which was 15.87±2.02 U/mg protein. Trend of amylase activities in stomach change appeared from low to high. The activity of amylase in intestinal canal kept at a higher level after 5h of feeding. At the same time, the results showed the activity of lipase in stomach changed quite acutely, which kept at a higher level after 3h of feeding, but the activity of lipase in intestinal canal changed slack. The effect to the activity of lipase in stomach by feeding was more distinct than the activity of lipase in intestinal canal. (4) Gastrin with proteolytic activity was isolated from gastric mucosa of northern sheatfish by salting out with ammonium sulphate of different concentration (optimum was 40% saturation) followed by gel chromatography on Sephadex G-75, which was purified 598-fold over crude extracts. SDS polyacrylamide gel electrophoresis showed two bands, the molecular weight of which was 34.0 kDa and 40.4 kDa. Its dependence of temperature and pH was determined. The curves were not typically bell-like. The proteolytic activity maximum was at 27 and 40℃, and at pH 1.9 and 4.6, which suggested the existence of more than one kind of proteinase. Northern sheatfish is ferocious carnivorous fish, its stomach capacity is big, and digestion ability is strong. Purification of Pepsin enzyme of northern sheatfish is significant to understand the nature of enzyme and digestive function.4. Growth and behavioral characteristics in early development stages of northern sheatfishThe results of artificial domestication in pond cultivation of northern sheatfish larvae show that initial feeding took place 2 days after hatching; the correlation between body length and daily age is L=5.4558 d-15.425,R2=0.9395; between body weight and daily age is W=0.0012e0.5012 d, R2=0.9901 within the 19 days old, while W=4×10-5L2.6364, R2=0.9968 within the 45 days old; the correlation between body weight and body length is W=0.0122L2.8105, R2=0.9968. The growth equation conveys that the larvae tend to be isogony along with the development proceed. Cover with water plants in rearing is better. Semi-intensive culture mode designed in laboratory and pond could avoid the self mutilation, and the application of it could contribute a lot in the commercial cultivation of northern sheatfish in pond.