**6. Concluding remarks**

The mitochondrial gene content and organization are highly conserved between Atlantic cod and human and strongly support a common functional platform. Similarly, the mitochondrial transcripts generating canonical mRNAs and structural RNAs are surprisingly similar. What about the newly proposed MDPs and noncoding RNAs? Are there any linage-specific differences? Research is still in its infancy, but recent findings suggest conservations between fish and mammals. More experimental studies in Atlantic cod and model systems like zebrafish are highly encouraged, including investigations of the fascinating mitochondrial swinger RNAs [24, 71, 72]. Mitochondrial-derived noncoding RNAs need to be profiled and further investigated in adult tissue types during normal and stress conditions, as well as at various developmental stages. A first step could be to study the intracellular location by in situ RNA hybridization and then ask if the noncoding RNAs are confined to the mitochondrial compartment or exported to the cytoplasm or other cellular compartments. Our studies in Atlantic cod indicate that at least two of the mitochondrial lncRNAs may serve as precursors for small RNAs. We conclude that vertebrate mitogenomes encode a significant number of gene products in addition to the 37 canonical OxPhos proteins, rRNAs, and tRNAs.
