Isolation, Identification And Epidemiological Investigation Of Parasitic And Bacterial Pathogens From Marina Culture Fish In Guangdong

The cage culture of marine fish has become one of the most important form of aquaculture production in our country in recent years. However, along with the rapid development of the marine aquaculture industry, many problems result in great losses in marine cage culture, such as excessive density, outdated facilities and poor management, which led to large-scale epidemic diseases. To provide reliable scientific data for prevention and treatment of marine fish diseases in South China Sea, the author took the whole year of 2007 to investigate the diseases of caged marine fish in the east and west of Guangdong Province. 216 fish of 21 species (10 families) were sampled every month, bacterial and parasitic pathogens were isolated and identified as follows:1. Isolation and identification of Streptococcus iniae: Conventional isolation, physiological and biochemical characterization, and the analysis of ITS were used and 4 Streptococcus iniae strains were successfully identified. The ITS of the isolates are highly homologous with 98% similarity. Specific PCR primers based on ITS were designed to identify Streptococcus iniae with high specificity and sensitivity (11.25 pg of bacterial DNA).2. Isolation and identification of Photobacterium damselae subsp. piscicida: Based on conventional isolation, physiological and biochemical characterization, and the analysis of ITS, 2 strains of Photobacterium damselae subsp. piscicida were successfully identified. The ITS of the 2 isolates are highly homologous with 99% similarity. Specific PCR primers of ITS were designed to identify Photobacterium damselae subsp. piscicida with high specificity and sensitivity (43.75 pg of bacterial DNA).3. Identification of Monogenea: Traditional morphological methods mainly based on opisthaptor and copulatory organ were used to identify and classify Monogenea collected from 133 fish samples. The results showed that the colleted Monogenea are categorized in 4 families, 8 genera as follows: Capsalidae Benedenia, Ancyrocephalidae Haliotrema & Tetrancistrus, Diplectanidae Pseudorhabdosynochus, Lamellodiscus & Telegamatrix, Microcotylidae Microcotyle & Polylabroides. Thereinto the article described the classification character of follow in detail: Neobendenia melleni, Haliotrema eukurodai, Haliotrema spirotubiforum, Haliotrema ampliocuspidis, Haliotrema fleti, Lamellodiscus japonicus, Pseudorhabdosynochus epinephel, Telegamatrix ramalingami, Microcotyle sp., Polylabroides sp., Tetrancistrum sp.4. Epidemic analysis of Streptococcus iniae and Photobacterium damselae subsp. Piscicida infections: The investigation showed that the average infection rate of the two pathogens was 2.78%. The average infection rate of Streptococcus iniae was 1.85%, and the highest infection rate was 5.56% in Collichthys crocea. The average infection rate of Photobacterium damselae subsp. piscicida was 0.93%, the highest infection rate was 10% in Siganus guttatus. Infection of P. damselae subsp. piscicida usually occurs in winter and spring, and infection of S.iniae occurs in summer usually.5. Epidemic analysis Monogenea infection: The highest infection rate of Monogenea was in November and reached 100%, the lowest infection rate was in July and reached 36%, and the average infection rate through 2007 was 61.6%. The infection rate of Monogenea in spring and winter was higher than that in the summer; the intensity of infection in summer and autumn was higher than in spring. The investigation showed that the infection rate of Benedenia, Haliotrema and Lamellodiscus were 20.4%, 19%, 7.9% respectively. Two or more species of Monogenea usually co-parasitized on one fish. Eight species of Monogenea were found on Acanthopagrus latus and 61.9% of the hosts were parasitized more than one species.