After Trim galore!, fastqc show the seuqence length is 20-151

Hi all, I run fastqc and multiqc and found that my RNA-seq has adaptors exists, after using trim galore! I run fastqc to see if the QC could be better, but the results show that the sequence length becomes a range that is from 20-151. I need a specific sequence length (that should be 150, from the fastqc result before trim galore!) to do RNA-star. But now it turned out to be a range, can anyone help me? btw, I tried cutadapt, but after cutadapt, I run fastqc, and it shows the adaptor is still there.

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Hi @Jiahui

Sequence reads are often represented by a range of lengths. RNA-Star is not restricted to 150 bases. But if you do want to filter by length for some reason, Trim Galore! has an advanced setting named Discard reads that became shorter than length N.

Maybe these tutorials will help more.