A comparative study was performed to evaluate the immunostimulatory effect of yeast and yeast-derived glucan in white prawn Fenneropenaeus indicus (sub-adults of ∼20 gm). Feed with a whole cell biomass of marine yeast Candida sake S165 (CSY) at a concentration of 10% (w/w) and another feed with 0.2% glucan of C. sake S165 (CSG) were used in the study. Fenneropenaeus indicus were fed with these diets for 40 days and subsequently challenged with the white spot syndrome virus (WSSV). Haematological parameters such as the total haemocyte count, phenoloxidase activity, superoxide anion (O2-) level, haemolymph peroxidase level and post-challenge survival against WSSV infection were determined to assess the immune status. In the present experiment, a higher immunity index and post-challenge survival were recorded in shrimps fed with the whole cell yeast diet. The better immunostimulatory performance of the whole cell yeast diet compared with the glucan diet could be attributed to the cellular constituents of yeast including the cell wall glucan, nucleotides, carotenoid pigments and vitamins. Here we observed that whole cell yeast performed better as an immunostimulant than the extracted cell wall glucans. Therefore, the use of yeast biomass in diets, rather than the yeast cell wall extract, glucan, would confer better protection against microbial infection besides reducing the cost of shrimp production.

Effect of an extraction method on the structure of glucan and its immunostimulatory response in Fenneropenaeus indicus was investigated. Here we extracted alkali insoluble glucan (AIG) and alkali soluble glucan (ASG) from a filamentous fungi Acremonium diospyri following alkali-acid hydrolysis and the sodium hypochlorite oxidation and dimethyl sulphoxide extraction method respectively. Structural analysis showed that 85% of glucan in AIG was a (1→3)-β-d-glucan and it increased the prophenoloxidase and reactive oxygen intermediate activity when administered to F. indicus. On the other hand, ASG, which contained 93% (1→3)-α-glucan, did not induce significant immune response in shrimp. Here we report that the difference in immunostimulatory potential between AIG and ASG is due to the difference in the percentage of (1→3)-β-d-glucans present in each preparation, which varies with the method of extraction employed. Also our observations suggest that glucan can be used as a potential immunostimulant to shrimp, provided it contains (1→3)-β-d-glucan as the major fraction.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Comparative analyses of genetic diversity, population structure and evolutionary relationships among co–distributed species can provide useful insights into fisheries management. In this study, mitochondrial DNA control region (mtCR) sequences were used to investigate genetic population structure and recruitment patterns of three co–occurring shallow water penaeid prawn species; Penaeus monodon, Fenneropenaeus indicus and Metapenaeus monoceros. These taxa dominate artisanal and commercial prawn catches in the Malindi–Ungwana Bay in Kenya, where juvenile prawns inhabit estuarine habitats, and adults occur further offshore, on mudbanks in the bay. A total of 296 [i.e. (P. monodon; n = 129), (F. indicus; n = 96), (M. monoceros; n = 71)] specimens were sampled from five sites; two estuarine nursery areas (juveniles), a nearshore mid–station (adults), and two offshore areas (adults). The sites were chosen to represent the bulk of the Kenyan fishery activities, and to include juvenile and adult cohorts that are presumably connected to each other through larval dispersal processes and migrations. Juveniles were obtained during 2010 from local fishermen, and adult prawns during 2011 using a commercial prawn trawler. Analysis of the mtCR sequences indicated high haplotype diversity (P. monodon; h = 0.9996 ± 0.0010; F. indicus; h = 0.9998 ± 0.0015; M. monoceros; h = 0.9815 ± 0.0110) for all three species. Genetic differentiation results for each species using AMOVA indicated no significant population differentiation (P. monodon; ΦST = 0.000, = p > 0.05; F. indicus; ΦST = 0.000, = p > 0.05; M. monoceros; ΦST = 0.0164, = p > 0.05) and pairwise ΦST statistics among sampling sites indicated the complete absence of spatial differentiation of female genes for all three species. In addition, the mtDNA data of P. monodon (i.e. n = 103) was augmented by using six polymorphic nuclear microsatellite loci. The pattern of panmixia was supported by the microsatellite analyses of P. monodon where AMOVA (i.e. RST = 0.00113, = p > 0.05), pairwise RST statistics (i.e. RST = 0.0000–0.0223, = p > 0.05) and STRUCTURE all confirmed the complete absence of genetic differentiation, among all sampled localities. Based on the absence of genetic population structure, each of the three species can be regarded as a single management unit throughout the Malindi–Ungwana Bay area. Spatial management strategies for prawn fisheries in the bay should therefore rely on factors other than genetic metapopulations, such as seasonal prawn recruitment and distribution patterns, ecosystem functioning and socio–economic implications to fishing communities and commercial trawl fishing companies. / AFRIKAANSE OPSOMMING: Vergelykende analise van genetiese diversiteit, bevolkings stuktuur en evolutionêre verwantskappe tussen spesies wat 'n verspreidingsgebied deel kan nuttige insigte lewer oor vissery bestuur. In hierdie studie was die mitokondriale DNS kontrole area (mtCR) volgordebepalings gebruik om die bevolkings genetiese stuktuur en werwingspatrone van drie mede-verspreide vlak water penaeid garnaal spesies; Penaeus monodon, Fenneropenaeus indicus and Metapenaeus monoceros te ondersoek. Hierdie taksa domineer die ambagtelike en kommersiële vangste in die Malindi-Ungwanabaai in Kenya waar, onvolwasse garnale in riviermondings voorkom en volwassenes in dieper waters op modderbanke in die baai voorkom. 'n Totaal van 296 [(P. monodon; n = 129), (F. indicus; n = 96), (M. monoceros; n = 71)] monsters was geneem vanaf vyf lokaliteite; twee in riviermondings (onvolwassenes), 'n nabykus mid stasie (volwasse) en twee diep water (volwasse) areas. Hierdie lokaliteite was gekies om die oorgrote meerderheid van Kenya se vissery aktiwiteite, asook die onvolwasses en volwassene kohorte te verteenwoordig wat vermoedelik geneties verbind is aan mekaar deur larwale verspreidingsprosesse en migrasies. Onvolwasse diere was verkry in 2010 vanaf plaaslike vissermanne en volwasse diere was in 2011 gekollekteer deur gebruik te maak van 'n kommersiële garnaal vissersboot. Analise van die mtCR volgorde bepaling het gewys dat daar 'n hoë haplotipiese diversiteit (P. monodon; h = 0.9996 ± 0.0010; F. indicus; h = 0.9998 ± 0.0015; M. monoceros; h = 0.9815 ± 0.0110) vir al drie spesies bestaan. Genetiese differensiasie resultate vir elke spesie, bepaal deur 'n AMOVA toets, dui op geen beduidende bevolking differensiasie nie (P. monodon; ΦST = 0.000, = p > 0.05; F. indicus; ΦST = 0.000, = p > 0.05; M. monoceros; ΦST = 0.0164, = p > 0.05) en paarsgewyse ΦST statistiek tussen die lokaliteite waar monsters geneem was, dui op geen ruimtelike differensiasie van die vroulike gene in al drie spesies nie. Hierbenewens is die mtDNS datastel van P. monodon (i.e. n = 103) uitgebrei deur ses polimorfiese kern mikrosatelliete in te sluit. Die patroon van mtCR panmixia was ondersteun deur die mikro-satelliet analise van P. monodon waar die AMOVA (i.e. RST = 0.00113, = p > 0.05), paarsgewyse RST statistiek (i.e. RST = 0.0000-0.0223, = p > 0.05) en STRUCTURE bevestig het dat daar totale afwesigheid is van genetiese differensiasie tussen alle vergelyk-te lokaliteite. Gebaseer op die afwesigheid van genetiese bevolking-struktuur kan elk van die drie spesies beskou word as 'n enkele bestuurseenheid deur die Malindi-Ungwanabaai area. Die bestuurstrategieë vir garnaal vissery aktiwiteite in die baai moet dus steun op ander faktore as genetiese meta-bevolking. Belangrike faktore om in ag te neem is seisoenale garnaal werwing en verspreidings patrone, ekosisteem funksionering en sosio-ekonomiese implikasies van vissers gemeenskappe en kommersiële visserymaatskappye.