Effects Of Dietary La³⁺,Ce⁴⁺ And Its Complex With Chitosan Oligosaccharide On The Growth,Non-specific Immune Response And Resistance Against Vibrio Splendidus Infection Of Sea Cucumber （Apostichopus Japonicus Selenka）

In recent years, rapid expansion and intensification of sea cucumber farming has led to the outbreak of infectious diseases and the current use of antibiotics would bring drug resistance, drug residues, environmental pollution and other issues. This paper explores the effects of dietary La3+, Ce4+, COS-La and COS-Ce on growth performance, nonspecific immunity and disease resistance of sea cucumber, Apostichopus japonicas. The main contents are as follows:1. Five isonitrogenous (18.6%) and isolipidic (1.1%) practical diets were formulated with graded level of La3+(0,10,25,50 and 75 mg/kg dry feed), respectively. Each diet was allocated to four replicates of sea cucumbers (Initial weight:6.72±0.02 g). Sea cucumbers were fed to apparent satiation once daily (17:00) for 8 weeks. During the experiment, water temperature was kept at 16±0.5℃, pH 7.8-8.2, dissolved oxygen beyond 5 mg/L, ammonia nitrogen below 0.5 mg/L, and salinity from 30 to 31%o. Results showed that the specific growth rate (SGR) of sea cucumber increased significantly from 0.90 to 1.24%/d as dietary La3+ increased from 0 to 50 mg/kg (P<0.05), and then decreased to 0.99%/d with further increase of La3+. Results of phagocytic activity and respiratory burst activity showed the same trend as SGR (P<0.05). Activities of superoxide dismutase (T-SOD), acid phosphatase (ACP) and alkaline phosphatase (AKP) in La3+(50 mg/kg) was significantly higher than those in La3+(0 mg/kg) (P<0.05). Meanwhile, the results of challenge test showed that dietary 50 mg/kg La3+ has lowest accumulative mortality (36.54%)(P<0.05). Therefore, dietary 50 mg/kg La3+ can significantly improve the growth and disease resistance of sea cucumber.2. The La3+ content in chitosan oligosaccharide lanthanum complexes (COS-La) was 8.82%, then five practical diets were formulated with graded level of COS-La (0. 150,300,600 and 1200 mg/kg dry feed), respectively. Each diet was allocated to four replicates of sea cucumbers (Initial weight:6.72±0.02 g). Results showed that COS-La can significantly promote the growth, phagocytic activity and respiratory burst activity of sea cucumber when the concentration of COS-La was 300 to 600 mg/kg (P<0.05), and then decreased with higher level of COS-La. Activities of T-SOD、ACP and AKP in COS-La (300 mg,600 mg/kg) was significantly higher than those in COS-La (0 mg/kg) (P<0.05), meanwhile, the accumulative mortality of former was 41.03% and 38.46%, which was significantly lower than the other groups (P<0.05). Compared to the results of first chapter, the concentration of La3+in COS-La was 26.46 mg/kg when the level of COS-La was 300 mg/kg. The activities of ACP and AKP in COS-La (300 mg/kg) were higher than those in La3+(25 mg/kg). Furthermore, accumulative mortality in COS-La (300 mg/kg,41.03%) was higher than those in La3+(25 mg/kg,53.85%). In conclusion, the immune stimulation effects of COS-La was obviously superior to La(NO3)3 when the concentration of La3+ was in the same level, this may due to COS could exert a synergistic effect in sea cucumber.3. Five practical diets were formulated with graded level of Ce4+(0,10,25,50 and 75 mg/kg dry feed), then an 8 week feeding trial was conducted to determine the effects of dietary supplementation of Ce4+on growth, immunity and disease resistance of sea cucumber (Initial weight 6.72±0.01g). Results showed that sea cucumber fed 50 mg/kg Ce4+had significantly increased in the SGR (P<0.05). Phagocytic index, respiratory burst, activity of ACP and AKP was reached the highest when the level of Ce4+ was at 75 mg/kg (P<0.05), but there was no significant difference among the activity of T-SOD and T-NOS (P>0.05). Result of challenge test showed that accumulative mortality in the group which fed with Ce4+(25 mg/kg,50 mg/kg) was lower than other groups, but there were no significant difference (P>0.05). Moreover, accumulative mortality in the group which fed with Ce4+(75 mg/kg) tended to increase. Overall, dietary supplement with Ce4+ could promote the growth of sea cucumber and enhance activity of immune enzymes; there was no obvious effect on disease resistance.4. The Ce4+content in chitosan oligosaccharide cerium complexes (COS-Ce) was 7.65%. then five practical diets were formulated with graded level of COS-La (0,150, 300,600 and 1200 mg/kg dry feed), respectively. Results showed that COS-Ce had a significant role on the growth of sea cucumber when the concentration of COS-Ce was 600 mg/kg (0.9-1.2%/d) (P<0.05), with the phagocytic index, respiratory burst and activity of immune enzymes (T-SOD, ACP and AKP) were significantly higher than those in control group (P<0.05). But when the concentration of COS-Ce was 1200 mg/kg, the indexes of the activities mentioned above showed downward trend, probably due to Ce4+in high dose of COS-Ce having an inhibitory effect on sea cucumber immune system. Challenge tests also showed that COS-Ce can enhance sea cucumbers’ability to resistance to Vibrio splendidus infection (33.33%), when the concentration of COS-Ce was 600 mg/kg (P<0.05). Compared to the results of the third chapter, the concentration of Ce4+in COS-Ce was 45.9 mg/kg when the level of COS-Ce was 600 mg/kg. The respiratory burst index and the activity of T-SOD in COS-Ce (600 mg/kg) were higher than those in Ce4+(50 mg/kg), and moreover, accumulative mortality of the former was lower than that of the latter. All above suggested that when the content of Ce4+was in the same level, COS-Ce was obviously superior to the single (NH4)2Ce(NO3)6 to improve disease-resistant ability of Apostichopus japonicas.