Characterization of marine oomycetes (lower fungi) infection in the eggs and larvae of mud crab (scylla tranquebarica)

Lee, Yih Nin (2016) Characterization of marine oomycetes (lower fungi) infection in the eggs and larvae of mud crab (scylla tranquebarica). Masters thesis, Universiti Malaysia Sabah.

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Mud crabs, Scylla spp. are important fisheries and aquaculture resources in Southeast Asia. The production of mud crab is mainly relied on wild caught seed stock but currently mud crab are over exploited by the fisherman due to high market demands. Therefore, seed production of mud crab has been considered as alternative way to overcome this obstacle. Seed production of mud crab Scylla tranquebarica had attempted several times at the mud crab hatchery in Universiti Malaysia Sa bah, but yet to success. The mortality of larvae reached almost 100% within 5 to 7 days after hatching in each attempt. After examination, marine Oomycetes (lower fungi) infection was found to be the reason behind mass mortality of eggs and larvae. Two kinds of lower fungi were isolated from the mud crab eggs and larvae at different spawning times. Based on the morphological observations, the isolated strains were identified as Lagenidium sp. and Haliphthoros sp. Both of the strains exhibited different modes of zoospores production. During zoospores liberation, the vesicle was formed at the tip of the discharge tube in case of L. thermophilum IPMB 1401 but not in Haliphthoros sp. IPMB 1402. Whereas, fragments were formed within the hyphae of IPMB 1402. Molecular comparison of nucleotide sequence ITS 1 region of IPMB 1401 and IPMB 1402 with other pathogenic Oomycetes isolated from marine crustacean to reveal the genetic cluster of fungi. As a result, IPMB 1401 showed high similarity of 99- 100% and grouped under the L. thermophilum cluster. The Similarity between the strain IPMB 1402 and Haliphthoros sp. group two was 97-100%. Based on the morphological and molecular identification, IPMB 1401 and IPMB 1402 were identified as L. thermophilum and Haliphthoros sp., respectively. Both isolated strains demonstrated to be obligatory marine fungus, where IPMB 1401 and 1402 were only able to grow on PYG agar containing seawater but not on PYG agar containing NaCI or KCI. Even though both strains were classified as obligate marine fungus, but they were only grow at certain range of salinities. Both strains showed no hypha I growth on PYG agar containing seawater at 10ppt and below. IPMB 1401 showed optimum growth at 30°C but hypha I growth was also observed at 350C. However, optimum temperature for the growth of strain IPMB 1402 was at 25°C to 30°C. Both strains were able to strive in wide range of pH conditions, but optimum growth was observed at pH 7. They showed different growth rates at pH 4 to 9. Both strains exhibited different levels of pathogenicity to Artemia salina. The strain IPMB 1401 showed no pathogenicity to Artemia, however the brine shrimp showed mortality at 20 and 20.3% after post challenged with zoospores of the strain IPMB 1402 for 24 and 48 hours. Besides this, in vitro fungicidal effect of formalin on hypha I growth and survival of zoospores were demonstrated using different formalin concentration and exposure time. The hyphal growth from an agar block and zoospores of the strain IPMB 1401 and IPMB 1402 were inhibited after 25ppm formalin bath for 24 hours. Mud crab larvae showed 10% mortality when exposed to 25 ppm formalin after 24 hours and high mortality was shown at 100 ppm formalin. The strain IPMB Therefore, this study suggests that 25ppm formalin bath for 24 hours can be effective in preventing fungal infection of both egg and larvae of mud crab Scylla tranquebarica.

Item Type: Thesis (Masters)
Uncontrolled Keywords: seed production, mud crab, high market demands
Subjects: Q Science > QL Zoology
Divisions: SCHOOL > Borneo Marine Research Institute
Depositing User: Munira
Date Deposited: 27 Feb 2018 07:49
Last Modified: 27 Feb 2018 07:49

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