Study of the Mandibular Bone Microstructure and Blood Minerals Bioavailability in Rainbow Trout (Oncorhynchus mykiss, Walbaum 1792) from Freshwater

SIMPLE SUMMARY: Bone deformities in the axial skeleton represent a frequent bone pathology in farmed salmonids, affecting the quality of life and even increasing mortality. Bone deformation can affect the formation, repair, and regeneration of inorganic-bone components and is associated with diet, culture conditions, and genetics. If diet and culture conditions are factors in the development of bone deformity, wild fish lack them and present fewer deformations than farmed fish. Hence, we studied mandibular bone microstructure using variable pressure scanning electron microscope (VP-SEM) coupled to EDS detector. Two groups of smolt rainbow trout were analyzed: Group 1, farmed fish with a control diet, and Group 2, wild fish without a control diet. We observed that serum protein levels remained within normal ranges. However, the calcium and phosphorus ratio was not the same in blood as in bone; phosphorus deficiency was more critical because it forms other structural molecules such as nucleic acid, phosphoproteins, phospholipids, and high-energy phosphates. Consequently, the microstructure in wild fish showed a more significant number of pores and microfractures per area, which was detrimental to the biomechanical properties of the bone. ABSTRACT: Farmed salmonids show alterations in bone structure that result in skeletal deformities during formation, repair, and regeneration processes, with loss of mineralization at the level of the axial skeleton, mainly the head and spine, affecting their quality of life and even causing death. Despite improving factors, such as farming conditions, diets, and genetics, bone alterations appear more frequently in farmed fish than in wild fish. Thus, we used SEM-EDX, and TGA-DSC to study bone mineralization in farmed and wild rainbow trouts. As expected, we found significant differences in the nutritional parameters of farmed and wild fish (p < 0.05). Microstructural analyses indicated that farmed fish have a more robust mineral structure (p < 0.05), confirming the differences in mineralization and microstructure between both groups. However, the mechanisms regulating absorption and distribution in the organism and their effect on bone mineralization remain to be known. In our study, the combined use of techniques such as SEM-EDX and TGA-DSC allows a clearer assessment and detailed characterization beneficial to understanding the relationship between diet control and bone microstructure.