Function to get the categories of custom taxonomy

Place the following function in the function.php file in the theme folder to get the categories under custom created taxonomy.

function get_the_category_by_taxonomy( $id = false, $tcat = 'category' ) {
    $categories = get_the_terms( $id, $tcat );
    if ( ! $categories )
        $categories = array();

    $categories = array_values( $categories );

    foreach ( array_keys( $categories ) as $key ) {
        _make_cat_compat( $categories[$key] );
    }

    // Filter name is plural because we return alot of categories (possibly more than #13237) not just one
    return apply_filters( 'get_the_categories', $categories );
}

call the function from your template file

$terms = get_the_category_by_taxonomy('','portfollio_category');

Here the $term contains an array of categories under the taxonomy 'portfollio_category'.