| Macrobrachium nipponensis is a kind of freshwater shrimp species commonly found in fresh water in China and Japan.Because of its delicious flavor and high edible value,it has become a hot spot for consumption and aquaculture.However,the ‘red gill disease’ that appeared in recent years has caused huge economic losses to the prawn farming industry,which has seriously restricted the healthy development of its industry.Based on a series of studies,it had been found that the appearance of ‘red gill disease’was closely related to a kind of eukaryotic parasite that could produce typical spores.This paper focused on the etiology,pathology and prevalence of the key culture areas.The specific research was as follows:1.Pathogen observation on ‘red gill disease’ of M.nipponenseIn order to ensure the ‘red gills disease’ of M.nipponense,it was the premise and basis of this study to identify the morphology and structure of the pathogen.The unstained gills rubbings of the diseased M.nipponense was observed.The results showed that compared with the normal cells,the gills of the disease M.nipponense were filled with a large number of spores and formed syncytids and inclusion bodies.Further observation by negative staining for transmission election microscopy(TEM)and scanning electron microscopy(SEM)showed that the spores were roughly irregular in shape,the surface was uneven,the diameter was about 5 μm,and the spores were obvious,which was consistent with the results of previous studies on spore parasites.The outer edge of cell wall had flat ribbons,which were highly similar to those of monosporidium reported.2.Histopathological study on ‘red gill disease’ of M.nipponenseIn this part,the histopathology of ‘red gill disease’ of M.nipponense was studied at both microscopic and ultramicroscopic levels.HE staining sections of gill tissue of M.nipponense were observed by optical microscope.It was found that after suffering from ‘red gill disease’,the gill filaments of M.nipponense showed local inflammation,including damage of gill filament cells,hypertrophy of gill filament,and black or red pigmentation.However,the presence of this parasite was not found in the intestinal organs,hepatopancreas,muscles and other tissues of diseased M.nipponense.At the ultra-micro level,ultra-thin sections of gill tissue of diseased M.nipponense were observed by TEM.It was found that there were large amount of spore aggregation around the nucleus of the gill filament cells of M.nipponense,indicating that the spores depended on the host cells for energy during growth.The inclusion of some spores without nuclei in the polynuclear inclusion body indicated that the spores were immature.Typical haplosporosomes with high density and deep staining were distributed on the outer cytoplasmic margin.3.Epidemiological survey of ‘red gill disease’ in M.nipponense breeding bases in Nanjing and ChangzhouThe epidemiological survey of several main shrimp farming areas in our province showed that the detection rate of ‘red gill disease’ in Wujin District of Changzhou city in 2017 was high,the symptoms were typical and the harm was serious.In 2018,followup surveillance continued in the region,and the incidence of disease decreased,with only sporadic occurrence in individual ponds.Other main areas,including Zhougang in Jiangning District and Yongning in Pukou District of Nanjing,had a low detection rate,although there was a widespread epidemic of ‘red gill disease’ in these areas from 2015 to 2016.These data indicated that ‘red gill disease’ presented typical periodic epidemic characteristics. |
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