Parasitic Infection And Physiological Ecology Of The Host Rice-field Eels Monopterus Albus In Dongting Lake

Rice-field eels Monopterus albus, whose meat are delicious and rich in nutrition, are of great value as food and drug. They are one of important aquatic products in China for export, and there is a good market for them. But the growth, development and reproduction of them are affected by parasitic diseases, and parasites in them decline the quality and value of them, so rice-field eel farmers suffer heavy economic losses. One of effective measure solving the problems is to learn parasitic disease mechanism fully and control over them. Parasitic infection of the host wild rice-field eels was investigated in Dongting Lake in Hunan Province, China. In addition, some physiological and biochemical values of the host rice-field eels(According to the number of parasites in rice-field eels, they were grouped under A, B and C three groups) of different infection intensity were tested by spectrophotometer, pH meter and biochemical analyzer, and the experiment data were analyzed statistically by using analysis of variance and multiple comparisons. The results were as follows:1. Primary parasitic infection of the host Monopterus albusThere were two species of primary parasites: Eustrongylides sp. and Pallisentis(Neosentis) celatus. They both showed aggregated distribution.The parasite Eustrongylides sp. infested mostly in abdomen cavity of the host Monopterus albus. Prevalence and infection intensity of Eustrongylides sp. were 40.60% and 4.13 respectively. When the body length of the host was below 40cm, they increased with the growth of the host Monopterus albus, but not when it was above 40cm.P. (N.) celatus parasitized mostly in foregut of the host Monopterus albus. Prevalence and infection intensity oiP. (N.) celatus were 41.52% and 9.35 respectively. The body length of the host Monopterus albus was positively correlated with prevalence and infection intensity, which increased with the growth of the host Monopterus albus.2. The effect of parasitic infection on intestines pH of the host Monopterus albusIntestines pH of the host Monopterus albus of different infection intensity infected with Eustrongylides sp. or P. (N.) celatus were tested and analyzed. Intestines pH of Monopterus albus infected with P. (AO celatus changed to a certain degree, but not with Eustrongylides sp. (P > 0.05).Foregut pH of the host Monopterus albus decreased with the increase in the number of P. (AO celatus. Midgut and hindgut pH of thehost slightly decreased with the increase in the number of P. C.N.) celatus, and the difference of midgut and hindgut pH between Group A, Group B and Group C was insignificant (P > 0.05).3. The effect of parasitic infection on the number of blood cells in the host Monopterus albusThe number of red and white blood cells per unit volume, and differential leukocyte count (DLC) (%) in the host Monopterus albus of different infection intensity infected withEustrongylides sp otP. (N.) celatus were tested and analyzed. The results of the host Monopterus albus infected with Eustrongylides sp. were almost similar to those of the host Monopterus albus infected with P. (N.) celatus.The number of red blood cells per unit volume decreased with the increase in the number of parasites in the host Monopterus albus.The number of white blood cells per unit volume increased with the increase in the number of parasites in the host Monopterus albus.Lymphocytes count (%) decreased with the increase in the number of parasites in the host Monopterus albus.Neutrophil count (%) increased with the increase in the number of parasites in the host Monopterus albus.Monocyte and Acidophil count (%) increased with the increase in the number of parasites in the host Monopterus albus. They showed a insignificant difference between Group A, Group B and Group C (P > 0.05).4. The effect of parasitic infection on digestive enzyme activities of the host Monopterus albusDigestive enzyme activities of digestive tract of the host Monopterus albus of different infection intensity infected with Eustrongylides sp. or P. (N.) celatus were tested and analyzed. Digestive enzyme activities decreased with the increase in the number of P. (N.) celatus in the host Monopterus albus, so did they with the increase in the number of Eustrongylides sp., but the difference was not evident (P > 0.05). The results of digestive enzyme activities of the host Monopterus albus infected with P. (N.) celatus showed that:Protease activity of stomach decreased with the increase in the number off! (N.) celatus in the host Monopterus albus.Protease, Lipase and Amylase activities of foregut decreased with the increase in the number of P. (N.) celatus in the host Monopterus albus. The difference of Lipase activity of foregut between Group A, Group B and Group C was not significant (P > 0.05).Protease, Lipase and Amylase activities of midgut decreased with the increase in the number of PAN.)celatus in the host Monopterus albus. The difference of Amylase and Lipase activity of midgut between Group A, Group B and Group C was not significant (P > 0.05).Protease, Lipase and Amylase activities of hindgut decreased with the increase in the number of P. (N.) celatus in the host Monopterus albus.