code: public function getMessagesByTopic($threadId, $limit = 25, $offset = 0)
      {
          $select = $this->getSelect()
                         ->where(array($this->threadIDField => $threadId));
          return $this->select($select);
      }
docs: getMessagesByThread
  
  @param int $threadId
  @param int $limit
  @param int $offest
  @return array of Zf2Forum\Model\Message\MessageInterface's