So I was going through my Codex in an attempt to complete my scans of all fishes, when I discovered that neither the Lobotriscid or the Flagellocanth appear when searched:
https://imgur.com/Kn6uwW9
https://imgur.com/10NfxIC
This clearly isn't intended behaviour, as other fish, such as the Chondricord appear without issue:
https://imgur.com/dL7nIrJ
I've also checked fish from the Plains and the Vallis, but none of them seem to share this issue. Hope to see it get fixed.