Investigation into the mortalities of larval mud crabs, Scylla serrata and methods of control

Pathogens and disease throughout the larval stage of the mud crab Scylla serrata are said to be responsible for preventing the establishment of a viable mud crab aquaculture industry within Australia. Vibriosis has been demonstrated as the underlying cause for inconsistent survival of larvae of the mud crab S. serrata (Mann et al. 1998). Initial investigations of this study were directed at gaining an understanding of virulence factors of vibrios, namely siderophores, haemolysin, chitinases and bacteriophages. Haemolysin, chitinase and siderophore activity were assessed through observation on specifically prepared agars. Detection of a bacteriophage was conducted by mitomycin C induced growth curves. It was visibly evident that the LLD1 strain of V. harveyi had the greatest haemolysin production compared to the other strains. The V. harveyi strain 12 produced the least haemolytic activity. Colony and halo diameter of the strains were as a group, significantly different (F=70.78,df=4, 100, P<0.0001) and (F=148.31,df=4, 100, P<0.0001) respectively. When examining chitinase activity, strains 12 and LLB2 were the only isolates that did not produce an evident zone of clearance. Colony and halo diameter of chitinases of the above strains were as a group, significantly different (F=41.46,df=5, 60, P<0.0001) and (F=118.03,df=5, 60, P<0.0001) respectively. It was visibly evident that the selected probiotic isolate V. harveyi LLB1 had the greatest siderophore production compared to the other strains. Colony and halo diameter of siderophores of the strains were as a group significantly different (F=22.79,df=4, 50, P<0.0001) and (F=172.97,df=4, 50, P