First of all I think your code has a bug in the while loop on one hand you are retrieving one record and storing it in the $trade variable, on the other hand when calling $action() you are retrieving another record so you are not processing half of the records with the $action and if your query returns only one record it won't get processed but it.

Secondly if you what to dump records I'd recommend you to use Data::Dumper, in the following form

UNTESTED

sub processTrades {
    my ($self,$action) = @_;
    my $count = 0;
    my $trdstmt = $self->_getTradesStatement();
    $trdstmt->bind_param(1,$self->{'startdate'});
    $trdstmt->bind_param(2,$self->{'enddate'});
    $trdstmt->execute(); 
    while(my $trade = $trdstmt->fetchrow_hashref()) {

        # Debug #
        use Data::Dumper;
        print STDERR Dumper($trade);
        # /Debug #

        &$action($trade); #Corrected#
        $count++;
    }
    return $count;
}
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