If you have any part of a fish, then it counts towards your limit. Since roe is part of the fish, if you have roe left over from a female but no meat left, it's still counting as 1 fish towards your possession limit.
Having said that, CO's have enough problems to worry about, that they will never in a million years ticket you strictly for having a little bit of roe push you 1 over the limit. If you have a conservation license, 2 salmon in the freezer, and a little bit of rainbow roe that you kept from the spring, no need to throw out your rainbow roe. Just be aware that roe is technically part of the fish, and next time around be more vigilant.
Also, if you purchased your roe, just as if you were to purchase your fish, this does not count as part of your possession limit. If you bought a 10 pack of salmon fillets at the store, or if you bought 1lb of rainbow roe, this has no bearing on your possession limit.
but heres the thing, the ministry has no way of identifying if the roe was purchased or if it was kept from a fish you had caught, unless you save your BoS from the bait shop or fish farm, but i know i don't, and i usually buy enough from a farm to last a season or 2