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Recent observations have revealed that most proto-planetary discs show apattern of bright rings and dark gaps. However, most of the high-resolutionobservations have focused only on the continuum emission. In this Paper wepresent high-resolution ALMA band 7 (0.89mm) observations of the disc aroundthe star CI Tau in the $^{12}$CO & $^{13}$CO $J=3$-2 and CS $J=7$-6 emissionlines. Our recent work demonstrated that the disc around CI Tau contains threegaps and rings in continuum emission, and we look for their counterparts in thegas emission. While we find no counterpart of the third gap and ring in$^{13}$CO, the disc has a gap in emission at the location of the secondcontinuum ring (rather than gap). We demonstrate that this is mostly anartefact of the continuum subtraction, although a residual gap still remainsafter accounting for this effect. Through radiative transfer modelling wepropose this is due to the inner disc shadowing the outer parts of the disc andmaking them colder. This raises a note of caution in mapping high-resolutiongas emission lines observations to the gas surface density - while possible,this needs to be done carefully. In contrast to $^{13}$CO, CS emission showsinstead a ring morphology, most likely due to chemical effects. Finally, wenote that $^{12}$CO is heavily absorbed by the foreground preventing anymorphological study using this line.

High resolution observations of molecular emission lines toward the CI Tau proto-planetary disc: planet-carved gaps or shadowing?