The agricultural activity differs from other activities in the accounting sense because of natural transformation of biological assets, i.e. the creation of new assets and its natural growth as well as the creation of agricultural products from that assets and their valuation on the reporting date. Due to these special features, accounting standards related to agriculture are set up with the argument that fair value is a better measure of the valuation of biological assets and agricultural products from its valuation at historical cost. This paper points to the effects of the recognition of income in the agricultural activity in accordance with the Croatian Financial Reporting Standard 17 and International Accounting Standard 41 on the long-term performance of the operations under unstable market prices on the example of mariculture activity. The analysis of income recognition over several reporting periods identified the effect of fair valuation of biological assets on the relevance of information obtained in the financial statements. The first part of the paper provides a theoretical framework for agricultural activity from the perspective of accounting standards in terms of recognition, measurement, and classification of biological assets and agricultural products as well as conditions for the recognition of state subsidies in agriculture. The importance of the FADN data collection system in agriculture and the similarity of its methodology with the accounting of income recognition has also been pointed out. Continued the explanation of the concept of fair valuation as well as income and expense recognition by measuring fair value. In the central part of the paper, on a practical example of mariculture activity, the impact of income recognition on long-term results was presented and a quantitative comparison of operational results was provided using the fair valuation method and historical cost method. The final section summarizes the arguments for the advantages of applying a fair method of evaluation in agriculture as well as the possible risks of its application in relation to the historical cost method. Also, there is a model proposed for recognition of income as result of fair valuation in agricultural activities under the conditions of variable market prices of biological assets and agricultural products.