If your data is tab separated you should split on a \t.

If you want your sum loop to count the number of elements in a row a better way would be

    for ( @$row )
    {
        $sum++;
    }
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If you want to print ';' separated you can just use a join. Although if you want this as input to some other program it may be safer to look at something like Text::CSV and set semicolon as the sep_char

print join( '; ', @$row );
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Couple of best practice notes; use warnings is preferred over -w and use 3 argument open.

Putting it all together, not sure it is exactly what you want but should help get you there.

#!/usr/bin/perl
  
use strict;
use warnings;

open my $fh, '<', "/tmp/Gene.txt" or die $!;

my @content = (<$fh>);

close($fh);

my @myArray;

for my $row (@content) {

    my @columns = split '\t', $row;
    push @myArray, \@columns;
}

my $title_row = shift @myArray;

for my $row (@myArray) {
    my $sum = 0;

    for ( @$row )
    {
        $sum++;
    }
    print "$row->[0] is $sum\n";    

    print join( '; ', @$row );
}
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