Study On Cryptocaryon Irritans Pathogenicity To Large Yellow Croakers(Pseudosciaena Crocea) And Its Clinic Control In Fujian Province

Cryptosporidiosis caused by a large number of Cryptocaryon irritans parasiticed in the gill and fish body surface.C.irritans has no host specificity,and with stronger environmental adaptability.Both juvenile and adult fish could be infected.Cryptosporidiosis spreads very quickly,and has a very high morbidity and mortality.if control measures didn't timely,all cultured fish would be die within 1 to 2 days.This study has been conducted to investigate the pathogenicity of C.irritans to large yellow croakers?Pseudosciaena crocea?,as well as the effect of Chinese herbal compound“HD-2”on inhibiting the generation reproduction of parasite C.irritans.Similary,the effect of HD-2 on the activity of serum immune enzymes of large yellow croaker was tested and a sustained-release disinfectant was developed.The results are showed as follows:1.The results showed that the number of total tomonts produced by P.crocea was positively correlated to the fish body weight?FBW?.Research on unit weight,FBW in250 g,100 g and 40 g could produce tomonts 8.12 ind/g,10.57 ind/g and 5.89 ind/g,respectively.The diameter of tomont was about 340.79±64.91?m and the hatching rate was around 76.39%.The theront could survive for more than 24 hours in vitro,its infection rate reached 91.61%,80.63%,57.27%,31.42%,9.50%and 0 after collecting for 0,4 h,8 h,12 h,16 h and 20 h respectively.The 90%lethal dose(LD₉₀)of P.crocea infected with C.irritans in 7 days was 9 712 theronts/fish,the median lethal dose for 50%(LD₅₀)was 4 366 theronts/fish.Infection experiment result showed that at 5 min,the theront had been entered the gill tissue.At 10 min,the theront had already attached to the filaments;at 30 min,several trophonts adhered to the gill filaments,and the filaments was slightly bent and deformed.After 1 h infection,the gill filament was deformed seriously and presented a wave shape.At 4 h,the gill filaments were swollen accompanied by cell shedding;part of gill filaments tissue hyperplasia and lumps formed in 12 h.At 24 h,swollen gills and the surrounding tissues were hyperplasia.At48 h,gill tissues adhered together to envelop the trophont.After 72 h of infection,the gill tissue was seriously damaged,lost the respiratory function,there was a circular cavity left after parasiticed.2.The survival rate of theront decreased with the increase of HD-2 concentration,i.e.,HD-2 concentration at 50 mg/L,80 mg/L,100 mg/L,200 mg/L and 400 mg/L could kill 0,20%,60%,80%,100%of theront in 4 h in vitro.P.crocea were fed pellet food with HD-2 for 30 days in each group?control,0;G1,5 g/kg;G2,10 g/kg;G3,15 g/kg?,with the increase of HD-2 concentration,the relative infection intensity decreased by31.98%,44.53%and 51.82%compared with the control group.After theront infection with LD₉₀,the fish survival rate of G1,G2,G3 was 40.00%,55.00%and 58.33%,which was much higher than the control group?only 8.33%?.Meanwhile,the trophont number in gill and pectoral fins greatly decreased within the medicated groups.After theront infection with LD₅₀,the tomonts produced from HD-2 treatment groups were significantly reduced,and their diameter were smaller than that from the control group.Similarly,the volume of tomonts reduced by 35.43%,36.14%and 37.26%,its hatching rate reduced by 16.28%,23.26%and 27.91%.HD-2 oral treatment for 15d to the diseased fish,results showed that the tomonts produced from fish in G1,G2,G3reduced 73.12%,87.7%,93.78%;the fish mortality rate of G1,G2,G3 was 58.33%,36.67%,and 21.67%,these much less than the control group?83.33%?.Microscopy observation illustrated that the“white spots”in gill filaments were greatly reduced within G1,G2,G3 groups.However,the gill filaments and pectoral fins had a large number of“white spots”in control group,and the remained fish in a moribund conditions.Therefore,HD-2 oral treatment could effectively interrupt the second infection of C.irritans,hold up the formation and development of tomonts,reduce the tomont hatching rate and the number of hatching theront,then inhibit the generation reproduction of parasite C.irritans.3.At the same time,this paper tested the activity of serum immune enzymes to discussed the influence of P.crocea immunity after fed the feed with different doses of HD-2.As the feeding time increases,the activity of lysozyme?LZM?in medicated groups showed a trend of increasing first and then decreasing.The maximum was all obtained at 21 d,10 g/kg and 15 g/kg group were higher.Add different doses of HD-2could significantly increase the serum superoxide dismutase?SOD?activity.At 21d each group reached the highest value,but SOD activity of 5 g/kg group and 10 g/kg group decreased at 28 d.The activity of alkaline/acid phosphatase?AKP/ACP?in medicated groups also showed a trend of increasing first and then decreasing.The maximum of AKP and ACP activity was both appeared at 21 d,and the value of 15 g/kg group was higher than the other groups at each sampling time point.The serum C3 and C4 contents in medicined groups increased significantly after 14 days compared with the control group.The serum C3 content reached the highest value at 21 d,though the C4 was showed at 28 d.And there was no significant change in the content of immunoglobulin M?IgM?in the serum from different groups.Both of the activities of catalase?CAT?and nitric oxide synthase?NOS?in serum showed a significant increasing trend after feeding HD-2.The activity of CAT and NOS in each group reached the maximum at 28 d,and the value of 15 g/kg group was the highest.4.Mixing calcium oxide and zeolite powder in a ratio of 1:1 and 1:2 could have a good bactericidal effect in the first 4 days,in 5 to 7 days could inhibit bacterial growth and maintain in a low level.Calcium oxide could effectively kill the C.irritans theront and tomont.Calcium oxide concent of 80 mg/L,20 mg/L and 40 mg/L could kill all the theronts in vitro in 10 min,120 min and 120 min respectively.Calcium oxide content of200 mg/L treatment could kill 100%tomonts in 1 hours,content of 150 mg/L,100 mg/L treatment for 2 h,4 h could also completely kill all tomonts.The sustained-release disinfectant mixed by calcium oxide and zeolite powder could effectivily reduce the trophont number in gill and pectoral fins of P.crocea,reduce the dead number,then relieve the condition of cryptosporidiosis.