I have many clients/patients that take one fish oil capsule and give one to the dog at the same time. Every preparation is a little different, different proportion of DHA or EPA plus many have additives like other vitamins, etc. Every preparation I have seen is appropriate for dogs in reasonable proportions.
We give Jill an OTC brand I got at Sam's Club rather than the dog preparation (we're on the road and getting a refill from my vet source isn't easy). She's just a little heavier than your Lab and is getting Nature Made 1200 (EPA 300 mg, DHA 300 mg).
This drug is almost impossible to overdose to a point of serious problems, you just get GI signs with too much oil.