Abstract: Generation and use of disease models, for instance in assays to identify and investigate genes and substances involved in disease and disease treatment, identification and use of drug targets. In particular, the present invention relates to generation and use of disease models in fish such as zebrafish. Gradable phenotypes may be generated in fish, allowing for degree of correction or alteration of an activity or effect of a treatment, gene or mutation to be assayed. Competing stimuli may be applied to fish in screens assaying for ability to affect an activity or effect of a treatment, gene or mutation. Example include any combination of an addictive drug, a visual stimulus, an audible startle stimulus, a temperature gradient, an electric shock, an aversive compound, a threatening shape or a dark area.