What is the key type for the ssh_host_key file in SSH?

In Ubuntu and Fedora in the /etc/ssh/ directory exists the following files:

ssh_host_key
ssh_host_dsa_key (not available in Fedora)
ssh_host_ecdsa_key
ssh_host_ed25519_key
ssh_host_rsa_key

For the same set of these files, exists others with the same names but with the .pub extension.

I know that dsa, ecdsa, ed25519 and rsa are keys type

Questions

• What is the key type for the ssh_host_key file in SSH?