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They edited embryos:

we determined whether a TDO-selective inhibitor (680C91) impeded pigmentation in developing embryos. The development of D. pealeii has been divided into 30 stages and eye pigmentation appears at ∼stage 25, while chromatophore pigmentation starts at stage 26 [21]. We added 680C91 to developing embryos at stage 20

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While you're right they edited the embryos the sentence you quoted is describing a drug (680C91) that they bath-applied to inhibit the TDO enzyme (as a positive control), rather than the CRISPR strategy they used, in which they injected the Cas9 and sgRNA into the embryo.

Oops, I should have quoted this part, from the summary:

Knocking out TDO in squid embryos efficiently eliminated pigmentation. By precisely timing CRISPR-Cas9 delivery during early development, the degree of pigmentation could be finely controlled.

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