Predicting the sacculinid Sacculina beauforti infection status of the orange mud crab Scylla olivacea by discriminant analysis

Parasitic sacculinids Sacculina beauforti infection is prevalent in the orange mud crab Scylla olivacea population in Marudu Bay, Sabah. Being a commercially important species and of high-value to the aquaculture and fisheries sector, this infestation on S. olivacea is alarming. Discriminant ratios were calculated based on the measurements of carapace width, abdomen width, gonopod length and pleopod length. A stepwise discriminant analysis was conducted and two discriminant functions were proposed for identifying infected males and females from the normal S. olivacea population. Only applicable in male, Function 1 incorporates five ratios and correctly classified 93.7% of individuals. Function 2 uses two ratios to identify infected females and has a success rate of 100%. When tested with the ratios of normal S. olivacea from other populations, Function 1 achieved 89-98% whereas Function 2 achieved 100% of re-classification success. These functions may serve as a fast, simple, inexpensive and non-invasive tool for identifying infected crabs rapidly when other methods such as molecular approach and direct identification based on the presence of externa are not applicable. The availability of this tool will aid in the control of S. beauforti infection by preventing them from being spread to other S. olivacea populations and/or aquaculture farms.