Using prefixes with Fuseki embedded

Question

I just started working with Fuseki and Jena. I have an ontology and I want to allow HTTP clients to send SPARQL requests and get the result. Here is the code I have in order to achieve that:

        // testing Fuseki
        Dataset dataset = RDFDataMgr.loadDataset("src/main/resources/files/test.owl");

        FusekiEmbeddedServer server = FusekiEmbeddedServer.create()
                .setPort(3332)
                .add("/ds", dataset, true)
                .build() ;
        server.start() ;

The Fuseki web server is working fine and I can send queries and get their results using a web browser.
The problem is whenever I try to use a prefix defined in the .owl file I get an error. Basically here is a simple request I want to send: http://localhost:3332/ds?query=SELECT ?test WHERE {?test ssn:observes ?o}
At the moment I get this error:

Error 400: Parse error: 
SELECT ?test WHERE {?test ssn:observes ?o}

Line 1, column 27: Unresolved prefixed name: ssn:observes

I know for sure the ssn prefix does exist in the .owl file. Is there a way I can get this request to work, knowing that I don't have access to Fuseki configuration file as I'm only using it through Java?