rake db:migrate (mysql)

Why i get this error?? What's means?

i have installed mysql2 gem, "sudo gem install mysql2"

Gemfile:

gem 'mysql2'
 

~: rake db:migrate --trace

rake aborted!
 dlopen(/Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle, 9): Library not loaded: libmysqlclient.18.dylib
   Referenced from: /Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle
   Reason: image not found - /Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle
 /Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle
 /Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2.rb:9
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:68:in `require'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:68:in `require'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:66:in `each'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:66:in `require'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:55:in `each'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler/runtime.rb:55:in `require'
 /Library/Ruby/Gems/1.8/gems/bundler-1.0.21/lib/bundler.rb:122:in `require'
 /Users/leonardo/dev/myproject/config/application.rb:7
 /Library/Ruby/Site/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
 /Library/Ruby/Site/1.8/rubygems/custom_require.rb:36:in `require'
 /Users/leonardo/dev/myproject/Rakefile:5
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/rake_module.rb:25:in `load'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/rake_module.rb:25:in `load_rakefile'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:501:in `raw_load_rakefile'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:82:in `load_rakefile'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:81:in `load_rakefile'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:65:in `run'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:63:in `run'
 /Library/Ruby/Gems/1.8/gems/rake-0.9.2.2/bin/rake:33
 /usr/bin/rake:19:in `load'
 /usr/bin/rake:19
 

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