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This review aims to analyse the use and effects of carotenoids in salmonid aquafeeds. Species of the family Salmonidae are of great interest for aquaculture due to their many properties, like fast growth and nutritional quality. Some species from this family are among the most farmed fish in the world. Thus, there are many studies on different farming technologies, fish biology, market dynamics and others. However, there are always new challenges in the aquaculture of salmonids, being a continuously improving activity. Consumers are becoming more considerate about what they choose to buy and consume. Thus, some aspects emerge as great influencers in the buying decisions of consumers, such as animal welfare, in addition to usual influencing factors, like product freshness and colour. A category of ingredients used in the salmonid aquaculture are carotenoids. They are pigments supplemented to diets for colouring the fish flesh, making it more appealing to consumers. However, some other benefits can also be observed, especially on the health of fishes. Be it synthetic or natural, carotenoids have become a largely used ingredient in salmonid aquafeeds. [ABSTRACT FROM AUTHOR]

The digestive system of fish is different from one species to another, depending on the type of food ingested. Danube salmon Hucho hucho (Linnaeus, 1758) is a critically endangered species of the Salmonidae family with the threat of extinction looming large, therefore conservation efforts are urgently needed. This study presents a detailed microscopic analysis of the Zeissl membrane in Danube salmon, through histological means. The biological material analyzed consisted of six fish raised in a specialized breeding farm for restocking purposes. Samples were collected from the gastrointestinal tract and processed using histological paraffin embedding. The Zeissl membrane was present in all studied segments, but its structure and development varied. It comprised the stratum compactum (SC) and stratum granulosum (SG). The SC formed a continuous membrane with unequal thickness in most of the studied segments, except for the cardia area of the stomach, where it appeared discontinuously, and the duodenum, where it only appeared between the apertures of the pyloric caeca. Aside from its role in limiting gastrointestinal distension, it may have other implications for the morphophysiology of the Danube salmon digestive tract. [ABSTRACT FROM AUTHOR]