Browsing by Author "Soyza, W.A.D."

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    Comparison of Blue Swimming Crab, Portunus pelagicus (Linnaeus, 1758) populations from Batticaloa and Trincomalee areas in Sri Lanka using Morphometric Parameters
    (Uva Wellassa University of Sri Lanka, 2018) Soyza, W.A.D.; Senevirathna, J.D.M.; Liyanage, N.P.P.; Jayamanne, S.C.
    Western, Northern and Eastern areas of Sri Lanka are famous for blue swimming crab fishery. However, very limited studies have been carried out to identify their population structure. This study investigated the utility of morphological characters to differentiate Portunus pelagicus populations of two different areas in eastern province of Sri Lanka. Samples were collected from Batticaloa (n=46) and Trincomalee (n=46) waters throughout its known geographic range. Twelve morphometric characteristics were measured up to nearest 0.01 mm. Discriminant Function Analysis (DFA) was performed to analyze significant intra-specific variations of two populations using standardized morphometric characteristics. The derived single discriminant function was totally accounted for 100% variance (Wilks' Lambda=0.74, P<0.05). The carapace width to carapace length ratio (CW2/CL) was recorded the highest canonical discriminant function coefficient (0.89), thus CW2/CL was selected as the most suitable parameter for the predicted model. The two centroids derived by DFA were 0.59 and (-0.59) respectively for the Trincomalee and Batticaloa, and predict the separation of two groups. According to the plotted graph, minimal overlapping between two groups was observed with possible variation between two populations. Two different allometric coefficients (b) were recorded as 2.92 (closer to isometric growth) and 2.76 (negative allometric growth) for Trincomalee and Batticaloa populations respectively. Hence, the results suggest that there is a possibility of having two P. pelagicus stocks in the 2 sites of the eastern part of the island. Changes of prevailing environmental conditions and habitat are the factors that lead to morphological differences of two P. pelagicus populations. Finding of this study is important for implementations of site-specific sustainable fishery management programs. Further, population genetic studies are recommended to confirm the results of the present study.
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    Development of Quality Assessment Guideline for Litopenaeus Vannamei (Whiteleg Shrimp) Post Larvae
    (Uva Wellassa University of Sri Lanka, 2020) Premarathna, N.M.C.N.; Athula, J.A.; Soyza, W.A.D.; Lakmal, J.A.S.
    Penaeus monodon is the main brackish water aquaculture species in Sri Lanka which targets the production for the export market. Litopenaeus vannamei (Penaeus vannamei) was introduced in 2018 as a new species expecting a rapid increase in production in the country. As a management strategy implemented by the National Aquaculture Development Authority (NAQDA), the assessment of post larvae quality is a compulsory requirement to obtain a better harvest via better growth without disease infections. Quality assessment of the P. monodon is based on 10 criteria and a minimum of 80% marks are required to get the approval for stocking. Up to now, the same assessment method has been used for P. vannamei, and due to some morphological and anatomical deviations; it did not totally comply with the new species. Hence, this study aimed to develop a post larvae quality assessment guideline for Litopenaeus vannamei with a score allocation procedure for each quality assessment criterion. The characteristics of different post-larvae stages (PL 1 - PL 30) from three different culture cycles of Litopenaeus vannamei were evaluated under each criterion and performed microscopically and morphologically. The microscopic observations were Monodon baculoviruses and Baculovirus penaeid, condition of hepatopancreas and gut content, necrosis and deformities, epibiont fouling, muscle opaqueness, and gut to muscle ratio of post larvae. The average body length, rostral spines, and size variation of each PL stage were the morphological observations measured to apply as standard values. The obtained values for post larvae of P. vannamei differed from the values of P. monodon. This study reveals the incompatibility of using the same assessment method for both shrimp species. Revision of marks allocation procedure, validation of the quality assessment method, and introduction as a new guideline will contribute to the future development of the Litopenaeus vannamei farming industry in Sri Lanka. Keywords: Litopenaeus vannamei, Post larvae quality, Quality assessment guideline, Shrimp farming