That's in fact a very good point.

It is highly possible that the cause for the betta's incredible sadness was the denial of its need to procreate.

The reproductive drive is so fundamental to life, especially in lower organisms that the lack of a mate has have serious consequences.

This has been observed in dogs, elephants (lone elephants - they're basically male elephants doomed to celibacy, which turns them into very violent creatures), and many other animals.

In fact humans are no exception. See the Psychology Today article "Ten Politically Incorrect Truths About Human Nature" - http://www.psychologytoday.com/articles/index.php?term=pto-4...