Hilary on the Seven Fish of Matt 15.34 - 36

"They brought forward seven loaves of bread. The Gentiles received no salvation from the law and the prophets. However, they live because of the grace of the Spirit whose sevenfold light, as noted by Isaiah, is a gift. (Isa 30.26 LXX) Therefore through faith in the Spirit the Gentiles receive salvation. They recline on the ground, for they were not subject to any works of the law or the flesh but were called in their earthly condition to the Spirit of the sevenfold light. The indefinite number of fish signifies the variety and dispensing of gifts and charisma, by which a diversity of graces satisfied the faith of the Gentiles. Moreover, the fact that seven baskets are filled indicates the overflowing and multiplied abundance of the Spirit of sevenfold light. What he generously gives, abounds. Having been satisfied, the gift becomes ever more richly endowed and full." (Hilary of Poitiers, On Matthew 15:10)

It was almost standard in the Church Fathers of the time to speak of 'the seven spirits of God' and 'the seven graces of God' (cf. Augustine, Chrysostom etc). Hilary is just avoiding giving a specific number cf:

For hence it is that twelve of them were chosen, who should be replenished with the perfection of the sevenfold grace of the Spirit. As from the number seven we rise to twelve; for seven multiplied in its component parts is extended to twelve; for whether four be taken by three or three by four, seven is changed into twelve, and hence, forasmuch as the holy Apostles were sent to proclaim the holy Trinity in the four quarters of the globe, they were chosen twelve in number, that by their very number they might set forth that perfection, which they proclaimed both by their lips and in their lives. [Gregory the Great, Moralia 1.19]