Use FIXTURES=table_1,table_2 if you want to specify

extract_fixtures.rake

desc 'Create YAML test fixtures from data in an existing database.
  Defaults to development database. Set RAILS_ENV to override.'
namespace :db do
  namespace :fixtures do
    task :extract => :environment do
      sql  = "SELECT * FROM %s"
      skip_tables = ["schema_migrations"]
      ActiveRecord::Base.establish_connection
      if ENV["FIXTURES"]
        tables = ENV["FIXTURES"].split(",")
      else
        tables = (ActiveRecord::Base.connection.tables - skip_tables)
      end
      tables.each do |table_name|
        i = "000"
        File.open(Rails.root.join("spec/fixtures/#{table_name}.yml"), 'w') do |file|
          data = ActiveRecord::Base.connection.select_all(sql % table_name)
          file.write data.inject({}) { |hash, record|
            hash["#{table_name}_#{i.succ!}"] = record
            hash
          }.to_yaml
        end
      end
    end
  end
end