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Extended phosphorus (P) deficiency has been linked to an increase of skeletal deformities in farmed salmonids. To date, X-ray examination still is the most practical way to detect abnormalities that are not externally visible. The aim of this study was to develop a standardized method based on empirical measurements that provides an early radiograph-based detection of deformities. Triploid all-female rainbow trout (60.8 +/- 1.6 g) were fed with phosphorus (P)-deficient and P-sufficient diets (total P = 0.5% and 0.92%, respectively). Experiments were carried out in 12 circular re-circulating tanks (n = 140/tank; 8.5-52.7 kg m(-3); 12 +/- 0.3 degrees C; 18L: 6D). All fish were x-rayed at week 5, 15 and 24 to monitor vertebral abnormalities. Fish were assigned to a vertebral phenotype (normal, biconcave or compressed) when all vertebrae of the caudal region (V31-44) showed the same type of abnormalities. At week 9, 18 and 27, ten fish per tank were randomly sampled according to their vertebral phenotype. Vertebrae V38-V39 were collected and a second X-ray was performed to confirm the above-mentioned phenotypes. Morphometrics (vertebral length and height; intervertebral distances and vertebral body angles) were measured directly on radiographs. For all parameters measured, comparisons were made between normal P-sufficient fish and different scenarios of vertebral development (normal, restored, stable and aggravated) in P-deficient fish. The two parameters showing the most sensitivity were the median intervertebral distance and dorsal/ventral vertebral endplate angles. When analysed together, these two parameters allow a quantitative distinction of the different vertebral phenotypes. Measuring dorsal/ventral vertebral endplate angles seems a promising approach to detect aberrant vertebral development at early stages as slight changes were observed in P-deficient vertebrae that were assessed as normal by visual examination. Further studies including histological examinations and comparison with other radiological imaging techniques are required to confirm these results.

International audience; Severe bone resorption of the vertebral body in reared rainbow trout was thought to be a dysfunction in mineral balance induced by increased growth rate in unfavourable rearing conditions. To verify this assumption, we sampled market-sized trout (c. 250 g) from 20 fish farms with different rearing conditions. Growth rate was also studied by sampling trout reared in three different water temperatures from fry to market-size. Transverse sections of vertebrae were microradiographed, then digitized. Total bone area (Tt-B.Ar.) and bone profiles were obtained using BONE PROFILER 3.23 software and a mathematical model was developed to statistically compare bone profiles using 12 parameters in four vertebra regions. Tt-B.Ar. and bone profiles were found to vary with rearing conditions and growing temperatures, indicating obvious influences of these factors on bone remodelling. However, vertebral resorption was found to be a general phenomenon. In trout from 190 to 235 mm in length, vertebrae underwent important remodelling resulting in large resorption of the middle area, while the transition and peripheral areas showed an increase in bone deposition. Changes in vertebra architecture seem to be a good compromise between the need to mobilize stored minerals during growth while maintaining vertebral biomechanical properties.