As part of a wider research project aimed at developing management strategies based on the current toothfish assessment methodology using the Generalised Yield Model (GYM), a Java version of the GYM has been developed. The new version has been developed directly from the specifications kindly provided by Dr Andrew Constable. Some routines have been translated from the GYM FORTRAN code into Java. As such, if sufficiently similar results can be obtained from the JGYM and the current GYM given identical input, then this would be a major step towards a verification of the GYM. This paper, which will be given in the form of a Power Point presentation, will discuss how the JGYM was developed, indicate differences from the GYM where they exist, and compare results from the two programs with identical inputs.