This paper is dealing with microeconomic aspects of the rainbow trout production. Although this production is in expansion in Serbia in recent years, it is evident an absence of proper recording, planning and analyzing of economic results and costs in the enterprises and farms dealing with aquaculture. In this paper it is shown one of the possible methodological ways for recording and calculating the economic parameters in this production. Through utilization of direct-costing method i.e. calculation which takes in account only direct and proportional variable costs of production, the economic parameters on one fish farm could be recorded and calculated in one relatively easy and quick way. The direct-costing calculations could be very useful managerial instrument for economic decision-making both in rainbow trout production and in other kind of aquaculture.