Abstract
The growth of fishes and their metabolism is highly variable in fish species and is an indicator for fish fitness. Therefore, somatic growth, as a main biological process, is ecologically and economically significant. The growth differences of two closely related salmonids, rainbow trout (Oncorhynchus mykiss) and maraena whitefsh (Coregonus maraena), have not been adequately studied as a comparative study and are therefore insufficiently understood. For this reason, our aim was to examine muscle growth in more detail and provide a first complex insight into the growth and muscle metabolism of these two fish species at slaughter size. In addition to skeletal muscle composition (including nuclear counting and staining of stem and progenitor cells), biochemical characteristics, and enzyme activity (creatine kinase, lactate dehydrogenase, isocitrate dehydrogenase) of rainbow trout and maraena whitefish were determined. Our results indicate that red muscle contains cells with a smaller diameter compared to white muscle and those fibres had more stem and progenitor cells as a proportion of total nuclei. Interestingly, numerous interspecies differences were identified; in rainbow trout muscle RNA content, intermediate fibres and fibre diameter and in whitefish red muscle cross-sectional area, creatine kinase activity were higher compared to the other species at slaughter weight. The proportional reduction in red muscle area, accompanied by an increase in DNA content and a lower activity of creatine kinase, exhibited a higher degree of hypertrophic growth in rainbow trout compared to maraena whitefish, which makes this species particularly successful as an aquaculture species.
Highlights
Maraena whitefish, (Coregonus maraena, Bloch 1779) and rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) belong to the family of Salmonidae and are ecologically important for the Baltic Sea region and economically important for aquaculture production
These fishes will be marketed directly to the consumer. Because of this direct sale of C. maraena, our objective was to examine the skeletal muscles of this fish species in more detail at slaughter size under aquaculture conditions
Due to these values the RNA/DNA ratio was double in rainbow trout (Fig 1C)
Summary
Maraena whitefish, (Coregonus maraena, Bloch 1779) and rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) belong to the family of Salmonidae and are ecologically important for the Baltic Sea region and economically important for aquaculture production. Intensive restocking operations started in the 1990s in Finland and later other Baltic Sea countries joined [1,2,3] Through all these efforts the population of C. maraena could be stabilized, but is still on the red list as a vulnerable species [4]. Maraena whitefish is a species-rich genus of mostly cold-water benthivores that grow optimally at water temperatures between 13 and 18 ̊C like it is found in the Baltic Sea [5]. Today this fish is kept in aquaculture [6, 7]. The protein/DNA ratio is an index of cell size [17] because muscle cell size increases in hypertrophic growing fish
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