| Myxocyprinus asiaticus is a second class protected animal in our country and is native to China. With the maturity of artificial propagation, it has become an excellent variety. But higher mortality at early life stages of Chinese Sucker seriously restricts the farming industrialization and commercialization process.With an attempt to better understand the early life history of M. asiaticus and to provide useful information for improving their artificial reproduction technique, rearing management and recruiting natural stocks, the process of growth and survival were studied under controlled conditions, and the mechanism of physiological digestion and their ecological countermeasures were researched as well. The main contents are as follows:1.The larval Chinese Sucker with initial body length of12.53±0.2mm, weight of10.32±0.18mg were randomly divided into8groups, with4replicates each group, which was fed with Artemia (Art), Tubificidae (Tub), Microdiet (MD), Microdiet+Spirulina (MD+Spi), Artemia+Spirulina (Art+Spi), Tubificidae+Spirulina (Tub+Spi), Artemia+Microdiet+Spirulina (Art+MD+Spi) and Tubificidae+Microdiet+Spirulina (Tub+MD+Spi), respectively, for30days. The results showed that:(1) MD was not suitable for Chinese Suckers as single initial diet. The survival rates of treatment group with live prey were above90%during the initial feeding, while it is as low as 0.73±0.33%for MD and MD+Spi groups.(2) To a certain extent, adding of Spi in initial feeding could improve the survival rate of larval Chinese Sucker. The survival rate of group MD (0.73±0.33%) and group MD+Spi (24.99±5.3%) were significantly different (p<0.05).(3) The weight and total length of groups containing Tub was significant greater than the groups containing Art (p<0.05). The specific growth rate (SGR) of group MD and MD+Spi was not significantly changed during5-15days post hatching (dph) and16-30dph. The SGR of group Art+MD+Spi was increased with cultural time increased; and it is firstly raise and then declined in rest groups.(4) The type of initial feeding has significant effect on digestive enzyme activity, with a time dependent pattern. In15dph, the amylase activity of group MD was lowest, and groups of Tub and Tub+MD+Spi were highest with no significant differences (p>0.05); in30dph, the amylase activity of group Tub+Spi, Tub+MD+Spi and group Art were similar (p>0.05), but were significantly higher than those of the rest groups (p<0.05). The larvae’s trypsin activities of group MD and MD+Spi were lowest and had no significant differences (p>0.05), and that of group Tub+Spi was highest. In15dph, The larvae’s lipase activities of group Art and group Tub were highest, however, no significant difference was observed with that of group Tub+Spi (p>0.05), but obviously higher than the other groups (p<0.05); In30dph, The larvae’s lipase activities in group MD+Spi was lowest, and highest in group Tub+MD+Spi, which was obviously higher than those of others (p<0.05). In15dph, the activity of alkaline phosphatase wasn’t obviously different between the treatment groups (p>0.05). However, it was lowest in group MD in30dph, with a significant lower level than that of group Tub+Spi (p<0.05) and no obviously difference with other groups (p>0.05).(5) Different initial feeding had a great effect on the liver and intestinal tissue morphological index of M. asiaticus larvae (p<0.05). The hepatocyte density of group MD was5189.31±124.28individual/mm2, which was significantly higher compared with other groups (p<0.05). The group Tub+Spi was the lowest (1835.42±195.56individual/mm2). The different initial feeding also had effects on the height and width of hepatocyte. The height and width of hepatocyte of the group MD and MD+Spi larvae are smaller than those of other groups. In the group which was fed with MD only, the hepatocytes were smaller, with indistinct border and deeply stained cytoplasm. The lumen diameter of foregut, midgut and hindgut were smaller, and the quality and height of intestinal fold were high significantly less than the other groups. Degenerated intestinal fold in the midgut was observed, and the number of intestinal fold in hindgut is almost zero. The morphological indexes described above were critical different with those of groups fed with live prey.2. Investigate on effects of weaning on the growth, survival and digestive activities of larvae and juvenile M. asiaticus were also performed. Based on the former results, the number of testing individuals for each group was slightly adjusted. The whole testing M. asiaticus was also randomly divided into8groups, with3triplicates per group and150fishes per replication. Triplicates from the treatment group with Art as initial feeding were kept the same diet after40dph, the other triplicates weaned to MD on40dph. Triplicates from the treatment group with Tub as initial feeding were kept the same diet after40dph, the other triplicates weaned to MD on40dph. The remaining six groups were weaned to MD on40dph.30days later, the survival rate, growth, and indexes of digestion were detected.(1) The weaning had an appreciable influence on early survival rate of M. asiaticus. The survival rate of group Art and Tub is88.52±5.23%and99.26±0.74%, respectively, with no noticeable difference (p>0.05). It began to remarkably decline on52dph, and dropped to17.41±9.17%,41.11±2.58%on70dph for weaned group Art and Tub, respectively. There was significantly different between the groups weaned and unweaned (p<0.05). Before the stage of weaning, the addition of Spi in initial feeding and too much earlier intervention of MD could have certain impact on early survival rate of M. asiaticus. In these treatment weaned groups, group Art+Spi had the highest survive rate (up to75.55±9.69%).(2) Weaning had a great influence on the growth of Myxocyprinus asiaticus larvae and juvenile. The weight and length of six weaned treatment groups should be less than two unweaned groups. The SGR of unweaned group Tub was4.06±0.46%.day-1and significantly higher than the weaned group Tub (1.36±0.36%.day-1)(p<0.05), but the weaned and unweaned groups that took Art as initial feeding had no significant difference (p>0.05).(3) Weaning also had effects on the digestion of M. asiaticus larvae and juvenile. It had minor influence on amylase activity, but major on trypsin activities. Compared with the unweaned group, trypsin activity of the weaned group took Tub as initial feeding declined remarkably, which suggested that pancreas of larvae and juvenile could not fully adjusted to some ingredients of MD. While trypsin activities of the weaned and unweaned group took Art as initial feeding had similar changing trend after40dph. The lipase activity of the unweaned groups which took Tub or Art as initial feeding were different during30-65dph, and were significantly different at45dph (p<0.05), with close changing trend after weaning, however. These results indicate that that weaning could have effects on lipase activity. From higher alkaline phosphatase activity in weaned group Art+Spi, we inferred that these larval had better nutritional status. Co-feeding groups had a lower alkaline phosphatase activity after weaning, which could be due to over the long duration or begin too early.(4) Co-feeding groups had stable digestive physiology after weaning, but not very well at growth and survival rate, which might relate to high proportion of MD.Finally, based on the all the above results, some suggestions are put forward for productive practice:it is better to use Art as initial feeding, supplemented with Spi as auxiliary. With the development of larval, co-feeding can be started at about20dph, then gradually increase the amount of MD, and decrease the Art until40dph. |
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