diff --git a/app/controllers/v1/collections_controller.rb b/app/controllers/v1/collections_controller.rb
index 195f6023552e7864fb1c165b0444b3558646cf3a..2deb8b8d2adfa62f66afa2d048d188874fe38124 100644
--- a/app/controllers/v1/collections_controller.rb
+++ b/app/controllers/v1/collections_controller.rb
@@ -11,7 +11,9 @@ class V1::CollectionsController < ApplicationController
   # GET /v1/collections
   # GET /v1/collections.json
   def index
-    render json: Collection.all
+    limit = params[:limit] || 10
+    offset = params[:offset] || 0
+    render json: Collection.limit(limit).offset(offset)
   end
 
   # GET /v1/collections/1
diff --git a/app/controllers/v1/learning_objects_controller.rb b/app/controllers/v1/learning_objects_controller.rb
index e2df8d39221a36584fbc14e8f4c59fb61c8cb866..19588ceb19cb620fb43dda41fddd0f3f389478f2 100644
--- a/app/controllers/v1/learning_objects_controller.rb
+++ b/app/controllers/v1/learning_objects_controller.rb
@@ -12,8 +12,10 @@ class V1::LearningObjectsController < ApplicationController
   before_action :authorize!, only: [:show, :update, :destroy]
 
   def index
+    limit = params[:limit] || 10
+    offset = params[:offset] || 0
     serializer = params[:obaa].nil? ? LearningObjectSerializer : LearningObjectObaaSerializer
-    render json: LearningObject.limit(limit).offset(offset).all, each_serializer: serializer
+    render json: LearningObject.includes(:tags, :publisher, :language, :license).limit(limit).offset(offset), each_serializer: serializer
   end
 
   # GET /learning_objects/1
diff --git a/app/controllers/v1/search_controller.rb b/app/controllers/v1/search_controller.rb
index b104a2b97d80a460a47ff3b9ebaa08325bf0f667..98563378a3b2b1cd254a72e6c27ad1d36ed66c1c 100644
--- a/app/controllers/v1/search_controller.rb
+++ b/app/controllers/v1/search_controller.rb
@@ -5,7 +5,7 @@ class V1::SearchController < ApplicationController
   # GET v1/search.json
   def index
     render json: SearchService.search(@search, current_user), status: :ok
-  rescue SearchService::InvalidSearchError => e
+  rescue SearchService::InvalidSearchError
     render json: @search.errors, status: :bad_request
   end
 
@@ -13,7 +13,7 @@ class V1::SearchController < ApplicationController
   # GET v1/search/autocomplete.json
   def autocomplete
     render json: SearchService.autocomplete(@search, current_user), status: :ok
-  rescue SearchService::InvalidSearchError => e
+  rescue SearchService::InvalidSearchError
     render json: @search.errors, status: :bad_request
   end
 
diff --git a/app/models/concerns/thumbnailable.rb b/app/models/concerns/thumbnailable.rb
index e22d871bfba9593fbd6f1790d20410631cef7d0c..123ffb7de4f048ba8e712fe8e04d1e6f39899613 100644
--- a/app/models/concerns/thumbnailable.rb
+++ b/app/models/concerns/thumbnailable.rb
@@ -2,7 +2,7 @@ module Thumbnailable
   extend ActiveSupport::Concern
 
   included do
-    has_attached_file :thumbnail, styles: { medium: '530x300', small: '250x140' }, default_url: 'learning-object-preview.png'
+    has_attached_file :thumbnail, styles: { medium: '530x300', small: '250x140' }, default_url: ''
     validates_attachment_content_type :thumbnail, content_type: ['image/jpg', 'image/jpeg', 'image/png', 'image/gif']
   end
 
diff --git a/app/models/concerns/trackable.rb b/app/models/concerns/trackable.rb
index 4da704bf74b767eec43d45afab93bb1455f59e42..c0b2c747e084b47917e7cdbe140ad5829f25f807 100644
--- a/app/models/concerns/trackable.rb
+++ b/app/models/concerns/trackable.rb
@@ -3,7 +3,7 @@ module Trackable
   include PublicActivity::Model
 
   included do
-    tracked owner: proc { |controller, _model|
-      _model.try(:user) || _model.try(:owner) || controller.try(:current_user) }
+    tracked owner: proc { |controller, model|
+      model.try(:user) || model.try(:owner) || controller.try(:current_user) }
   end
 end
diff --git a/app/services/search_service.rb b/app/services/search_service.rb
index d95fe90014fe5fa37998d74c91bad69bae7e3bed..c8883fcea7c33a44f98a823040b1fca12feecc03 100644
--- a/app/services/search_service.rb
+++ b/app/services/search_service.rb
@@ -1,7 +1,7 @@
 module SearchService
   SEARCH_CLASSES = %w(LearningObject Collection User)
 
-  class InvalidSearchError < StandardError; end;
+  class InvalidSearchError < StandardError; end
 
   def self.search(search, user)
     model = instance(search, user)
@@ -13,8 +13,6 @@ module SearchService
     model.autocomplete
   end
 
-  private
-
   def self.instance(search, user)
     raise InvalidSearchError unless search.valid?
     "SearchService::#{search.search_class}".constantize.new(search, user)