Factors contributing to ocular pathologies in fish

Introduction. With the decline in industrial salmon catches, fish hatcheries play a crucial role in replenishing stocks of these commercially valuable fish species. In aquaculture conditions, salmonids often demonstrate eye lesions, which reduce their adaptability in natural environments. Diagnosing these pathologies enables their classification by causative factors and development of therapeutic and preventive measures. Objective. To search for and summarize scientific publications on ocular pathologies in salmonids at facilities engaged in industrial breeding, commercial farming or reproduction in Asia, America, Europe, and the Russian Federation. Materials and methods. A search for Russian- and English-language articles in PubMed, Scopus, Web of Science, and eLIBRARY.RU databases was conducted. To prepare the review, 44 research papers published between 1975 and 2024 were used. Results. The study demonstrates that eye lesions in Atlantic salmon ( Salmo salar ), brown trout ( Salmo trutta ), and rainbow trout ( Oncorhynchus mykiss ), such as non-parasitic cataracts (lens opacity), keratopathy (corneal opacity), and unilateral or bilateral exophthalmia (eye protrusion), are reported at fish hatcheries and aquaculture facilities in the Northwestern region of the Russian Federation, as well as in several foreign countries. Eye lesions lead to decline in immunophysiological state and growth rates in aquaculture, reduction in the number of healthy fish, increased feed costs, and release of substandard fish from hatcheries into natural water bodies, sometimes resulting in their mortality. Basic information on factors contributing to the development of ocular pathologies in salmonids is presented. An analys is of therapeutic and preventive measures for eye lesions is provided, highlighting the importance of a differentiated and causative factor-dependent approach. Conclusion. In global veterinary practice and fish pathology, the problem of eye protrusion in fish remains understudied, with limited research on the topic. This review analyzes and differentiates the key factors contributing to the development of ocular pathologies in salmonids. Identifying these factors will enable early diagnosis, determination, and development of preventive measures or effective treatment regimens, ultimately preserving fish health, improving the productive capacities of aquaculture establishments, and reducing economic losses.