Ontology creation and document indexing are well-known, critical bottlenecks for integrating semantic services and in general for bootstrapping the Semantic Web. For certain domains or communities, legacy terminologies and indexing methods exist which can be reused effectively. In the Fishery Ontology Project (FOS), we have reengineered and aligned legacy thesauri by using formal ontological methods, and we are deploying the resulting ontology library (currently including more than 35,000 classes and about 10,000 individuals) for services dedicated to fishery document repositories and databases. Alignment, reengineering, and modularization of the library leverage on the Core Ontology for Fishery developed in FOS. Its structure and use are described in this paper