Are there any visible differences between Baltic cods and Atlantic cod?

Visible as in visible from the outside

Welcome to the forum! I’m not sure what you mean by Baltic cod? It doesn’t look like any species of cod I can find online. Is it possible that Baltic cod is another name for Atlantic cod?

That is what I was thinking. Its just that I found out that the species name Gadus morhua callarias exists and I am not sure where the difference comes between that name and just Gadus morhua (Atlantic cod).

It looks like Gadus morhua callarias isn’t recognized by iNaturalist, although others such as ITIS do have it. Gadus morhua callarias would just be a subspecies of Gadus morhua. Like many other subspecies, I think the best differentiation would be in range.

From what I found, this seems like the proper range for the subspecies.
Gadus morhua morhua - West Atlantic
Gadus morhua callarias - East Atlantic
Gadus morhua kildinensis - Around Kildin Island

Again, I’m not certain if these subspecies are even recognized and if you’re planning to identify them on iNat, you can only go to species. I hope this helps!