Some accents to note

06

104

757

1424

Matthew 7:10 ἰχθῦν αἰτήσει not ἰχθὺν αἰτήσει (of course this affects the nominative and accusative singular of ἰχθῦς and ὀσφῦς elsewhere).

03

011

017

021

But 

481

1424

In assessing the differences between witnesses, we can take into account how smart, consistent, deliberate and grammatically knowledgeable each scribe was in matters of accentuation. The accentor of Vaticanus (B 03) is particularly deliberate and accents ἰχθῦς, ὀσφῦς and ὀφρῦς consistently, including for the genitive singular, e.g. Luke 11:11, against Herodian’s rules:

In this it was isolated, so we didn’t follow it in the THGNT. Minuscules tended to replace circumflexes with acutes and graves. This is but a grammatical trifle, but we had fun discussing it in preparing the THGNT and learning from Patrick James, who is, according to Dirk Jongkind the only person he knows who truly knows ancient Greek.

With thanks once more to CSNTM and the Vatican Library for images.