Fishmouthing shingles is a term given to curled shingles that have the appearance of the mouth of a fish. It typically occurs at the lower front tab edge or along the cut-out edge.
These imperfection may be more noticeable depending on the pitch of the roof. Sunlight and the colour of the shingles can also accentuate that look. It may not always affect the life of the shingle, chances of water / moisture penetration into the building or resulting wind damage it can.
Fishmouthing can be caused by nails or staples that raise up out of the roof sheathing; something under the shingle that likely shouldn’t be there; underlayment or felt on the roof sheathing not laying flat; and, shingles that are damaged or bent prior to their instalation.
Typically, this shingle condition is corrected by sealing / gluing the shingles flat or their replacement.