The Proto-Indo-European word *laks-
Word *laks-
Meaning salmon
See also Tocharian B: laks ‘fish’

Comments
Toch. laks/läks, ON lax, Lith. lašiša, Ltv. lasis, Russ. losos', Polish łosoś, Gm. lahs/Lachs, Eng. leax/--, Old Prussian lalasso

Other words that might be of interest
*dʰĝʰu- ‘fish’, *k̂on- ‘shell’, *peisk ‘fish’, *dhĝhuhₓ- ‘fish’, *karkr(o)- ‘crab’, *pik̂sk̂os ‘fish, trout’