Fish, being cold-blooded, don't suffer hypothermia in quite the same way that a mammal does. Their system just slows down to the point that it doesn't work anymore... but, clove oil or beheading seems to be faster and less painful.
As far as ecosystem damage goes....
If a fish CAN get past the sewer treatment plant, yes, it would be able to escape into the local waterways. It is doubtful it would survive that journey through hundreds of gallons of... well... you know. But, if there were a particularly tough fish out there, it might happen, you never know. People with septic tanks don't have that problem, but it's still a really nasty way of killing your fish, if you ask me. How would you like to die in a cesspool? Ugh....
When at all possible, I like to just let them die by natural means so I don't have to do it. Aggressive fish go back to the store, and sick fish die on their own in a quarantine tank. It is against my nature to kill anything.
As far as ecosystem damage goes....
If a fish CAN get past the sewer treatment plant, yes, it would be able to escape into the local waterways. It is doubtful it would survive that journey through hundreds of gallons of... well... you know. But, if there were a particularly tough fish out there, it might happen, you never know. People with septic tanks don't have that problem, but it's still a really nasty way of killing your fish, if you ask me. How would you like to die in a cesspool? Ugh....
When at all possible, I like to just let them die by natural means so I don't have to do it. Aggressive fish go back to the store, and sick fish die on their own in a quarantine tank. It is against my nature to kill anything.