No abstract

This study investigated the combined effects of photoperiod and dietary P level on bone osteoclast and osteoblast activity, and morphology, as well as plasma vitamin D status in Atlantic salmon post‐smolts. The fish were reared under continuous light (LL) or 12 h light/dark (LD) per day, and fed diets with insufficient phosphorous (P) (4 g kg−1 available dietary P, LP) or sufficient P (8 g kg−1 available dietary P, HP) for 79 days in seawater. LL significantly increased plasma 25(OH)D3 level and bone tartrate resistant acid phosphatase (TRACP) activity, and decreased bone collagen XI α1 chain (col11a1) mRNA transcription. The LP diet significantly increased plasma 1,25(OH)2D3 level and bone alkaline phosphatase activity, but decreased bone TRACP activity and matrix metalloproteinase 13 (mmp13) mRNA transcription, and vertebral mineral content, stiffness and length/dorso‐ventral diameter (l/d) ratio. A significant interaction between light and P was only observed on the l/d ratio, and the LP‐LL group was the only group that developed vertebrae with a compressed morphology (significantly lowest l/d ratio). In practical terms, these results show that Atlantic salmon post‐smolts under continuous light may need P supplemented diets to support normal bone development.

Vegetable oils (Vo) are an alternative to fish oil (Fo) in aquaculture feeds. This study aimed to evaluate the effect of dietary soybean oil (Vo diet), rich in linoleic acid, and of dietary fish oil (Fo diet) on the development of spinal deformities under bacterial lipopolysaccharide (LPS)-induced chronic inflammation conditions in Atlantic salmon, Salmo salar L. Fish [25 g body weight (BW)] were fed the experimental diets for 99 days. On day 47 of feeding (40 g BW), fish were subjected to four experimental regimes: (i) intramuscular injections with LPS, (ii) sham-injected phosphate-buffered saline (PBS), (iii) intraperitoneally injected commercial oil adjuvant vaccine, or (iv) no treatment. The fish continued under a common feeding regime in sea water for 165 more days. Body weight was temporarily higher in the Vo group than in the Fo group prior to immunization and was also affected by the type of immunization. At the end of the trial, no differences were seen between the dietary groups. The overall prevalence of spinal deformities was approximately 14% at the end of the experiment. The Vo diet affected vertebral shape but did not induce spinal deformities. In groups injected with LPS and PBS, spinal deformities ranged between 21% and 38%, diet independent. Deformed vertebrae were located at or in proximity to the injection point. Assessment of inflammatory markers revealed high levels of plasma prostaglandin E₂ (PGE₂) in the Vo-fed and LPS-injected groups, suggesting an inflammatory response to LPS. Cyclooxigenase 2 (COX-2) mRNA expression in bone was higher in fish fed Fo compared to Vo-fed fish. Gene expression of immunoglobulin M (IgM) was up-regulated in bone of all LPS-injected groups irrespective of dietary oil. In conclusion, the study suggests that Vo is not a risk factor for the development of inflammation-related spinal deformities. At the same time, we found evidence that localized injection-related processes could trigger the development of vertebral body malformations.

Inflammation is a non-specific protective mechanism towards injury known to affect bone remodelling. This study aimed to investigate the effect of Freunds complete adjuvant (FCA) induced-inflammation on the prevalence of spinal deformities of Atlantic salmon postsmolts fed with two different dietary P levels. Sextuple groups of salmon postsmolts were fed with either a low-phosphorous (6 g kg-1 available P, LP) or a high-phosphorous (9 g kg-1 available P) diet for a period of 101 days. On Day 102, individually tagged fish were subjected to (i) single injection with FCA (0.125 mg kg-1 BW) dissolved in phosphate-buffered saline (PBS) (ii) placebo injection with PBS or (iii) sham injection (insertion of needle only) or (iv) remained untreated. On Day 103, fish were given a common diet for 174 days in seawater. No significant differences in body weight were observed. Injected fish, particularly the FCA group, had more compressions in the injection site than untreated fish. No effect of diet and no interaction between treatment and diet were observed. Severe scoliosis was observed in similar to 7% of FCA-injected individuals, corresponding to a mixture of bone malformations in the tail region. In conclusion, experimentally induced inflammation may be an independent risk factor for bone deformities in Atlantic salmon