Intensive production of animals for food involves achieving the desirable slaughter weight in the shortest possible time. Growth rate is increased by means of breeding, optimizing access to and composition of feedstuffs, and rearing conditions.
An example is that in salmon farming, it is common to increase water temperature during early life stages in order to increase growth rate.
The challenge for agriculture as well as aquaculture as a business is that having a one-sided focus on rapid growth entails that production animals are more susceptible to certain types of diseases – e.g. circulation problems and skeletal deformities.
Elisabeth Ytteborg
Photo: Janne Brodin
Temperature exposure as a model High water temperature during the early stage of life has long been known to be one of the decisive factors for the development of deformed vertebrae in Atlantic salmon (Salmo salar), but the pathogenesis has until now not been extensively studied. Elisabeth Ytteborg has in her doctoral work at Nofima used temperature exposure as a model to study the development of fused vertebrae.
The project has been part of a larger platform project on deformities, led by senior scientist Grete Bæverfjord, and financed by The Research Council of Norway (NFR: 172483/S40). Her main supervisor has been scientist Harald Takle.
Varying temperature regimes In the main experiment, Atlantic salmon were exposed to two different temperature regimes: one high temperature regime, where spawn was kept at 10°C until start of feeding and at 16°C until approximately 60g size, compared with a control regime of 6°C until start of feeding, followed by 10°C during the second period.
Using X-ray screening, the vertebrae were separated into four groups, classified from normal to deformed. 20 specific genes playing central roles in the signal pathways for bone and cartilage development have been selected for molecular analyses. Among other things, these genes regulate the differentiation of stem cells into osteoblasts (bone forming cells), chondrocytes (cartilage cells) and osteoclasts (bone resorbing cells).
New findings give increased understanding The results show that temperature induced rapid growth leads to a softer bone structure, probably as a result of reduced mRNA production by genes involved in mineralization. Osteoblast activity is generally lower in fish from high temperatures, and remodeling and ossification of bone is reduced. Attempts to strengthen the spine through increased cartilage activity turned out not to be sufficient, in that more that 30% of the individuals exposed to high temperatures developed deformities.
By investigating two different stages of the fusion process, we found that fusion development involves structural and molecular changes in cartilage, bone and notochord. Central to the process are osteoblasts with disturbed/changed cell cycles, chondrocytes with changes to their maturation pattern and a shift from endochondral to transchondroid ossification. Furthermore, ISH displayed an increased number of cells expressing a mixture of markers that are normally specific to either osteoblasts or chondrocytes. The study points at new molecular finds in the fusion process, and adds to an increased understanding of temperature induced deformities in Atlantic salmon. This new knowledge will be an important tool for the salmon industry’s effort to optimize feed composition and production conditions in order to reduce the occurrence of deformities to an absolute minimum.
